Can someone walk me through the procedures?

diesel research · May 22, 2011

The recent code reader talk, got me to wondering. I don't own those basic code readers and have only used them a few times "for kicks and giggles". I prefer software/hardware with more capability.

Walk me through the procedures of using one of these code readers to solve a drivability issue or MIL.

Let's also assume since the person using a code reader is cheap enough to buy one of them, they do not have access to Alldata/Mitchell/FSM/wiring diagrams, do not have a scope, do not have "fancy" gauges.

Just a test light and the average $50 or less multimeter.

How do you troubleshoot a code? Let's say it is a P0300 just for grins.

Then we can add a P0340 on top.

Anyone able to walk me through the process? Swap cam sensor and coil pack and call it a day?

___________________
OR can some one explain as detailed as possible, how they solved their problem with only such a simple tool? What test procedures were used to verify?

justanengineer · May 22, 2011

Being a cheap SOB who turns wrenches only for fun now, I will give this a shot in the hopes of helping someone. First off, reading the definitions of those two codes posted on the net, I would suspect (and hope bc its cheaper) they are related. Cylinder misfire can be caused by any number of possible problems, so I consider that code second if the other doesnt solve the issue. To troubleshoot any sensor, I would start by locating the sensor and looking for obvious issues. When I turned wrenches for a living I swear I had more issues with harnesses going to sensors than I had with the sensors themselves. Sometimes its obvious, sometimes not, but look for the obvious first. If you see frayed wiring or anything melted - obviously replacement or repair is necessary. If nothing is obvious, I would pull the harness off the sensor and test the sensor itself. The better home repair manuals available at auto parts chains will actually tell you how to test many of the sensors using a multimeter, or if not possible they will tell you that too. They can also provide you with a cheap source of a basic wiring diagram. If the sensor checks out, I would follow the wiring diagram in each direction as necessary until the fault is found. This may not be the same way some of the more experienced techs would approach your problem, but I hope it helps regardless.

Stick · May 23, 2011

I believe I see what you are getting at. I'm going to wait and see some of the responses before I give it a shot.

diesel research · May 23, 2011

This is all hypothetical, mind you. I am sitting here with one of those cheap manuals so I can play along as well.

I am using a '99 vehicle for this example, one which runs on same principle as many other vehicles, no special quirks for this game.

If I go to symptom based troubleshooting in this book, it sends me on a wild goose chase. That is assuming I noticed a slightly longer crank time and the random misfire. (we don't know the sensor is dead, coulda been a fluke just once and no more symptoms)

Anywayys, it directs me to try some of the following:
Check choke operation
check for loose wires on starter
check fuel pressure
check cap and rotor
Adjust floats
check egr
compression/leak down test
check timing

Obviously that is getting me no where. Thats what I get for owning a vehicle that has 17 years of coverage in one book.

So I move on to sensor testing.

I look at cam sensor testing section and find out there ISNT ONE! Being a bit of a wise guy and knowing it is a hall effect and runs on same parameters, I check out the cranksensor section which mentions a simple resistance test between pin A&C. Of course this is not correct, but it's what the book suggests. Says if it reads "OL" replace it. If it does not read OL, well....it doesn't say anything else. Not to mention that was actually for cranksensor, I just happen to know they run on same parameters. No scopes to watch wave patterns, ect ect. No other suggestions from book.

So I give up and move to replacement chapter which tells me to remove distributor assembly and if I am not dead-nuts careful during reassembly, timing will be all screwed and will have to reset with a scan tool (not code reader)

So I do all of that and no dice. (keeping in mind this is hypothetical scenario) Spent the cash and time, well over $150 worth. Now I could remove it and warranty it, blaming autozone for the cheap sensor, or???

diesel research · May 23, 2011

FWIW, I had wafrederick replace the coilpack while he was at it.

I am not really asking for a parts list necessarily. I am *trying* to do things right. I don't need livedata and bidirectional control and mode$06 and all that, BUT I am trying to prove I can troubleshoot properly. So how do I continue with testing? Or are your parts suggestions part of the testing strategy?

I mean there are still tests that a person w/o scan tool could do, but my haynes is equally worthless and I wouldn't know which test to begin with. I could adjust the floats and make sure the choke is working properly, but I have a suspicion that is not in the right direction, and my "manual" doesn't go any further.

I can fix anything · May 23, 2011

Is it GM? If so does it have a distibuter? Yes, ok pop off the cap feel the large amount of play in the distributer gear. Replace dist. both codes gone. That was too easy. Lets do a p0420 with no info :spit:

Stick · May 23, 2011

diesel research said:
FWIW, I had wafrederick replace the coilpack while he was at it.

Bwahahaha... You owe me a new laptop keyboard now...

Stick · May 23, 2011

I can fix anything said:
Lets do a p0420 with no info

It needs two new O2 sensors and a reflash. Unfortunately you'll still have to take it to a shop for the reflash.... Well, maybe we should just throw the two O2 sensors and skip the reflash and see if that fixes it.

diesel research · May 23, 2011

I can fix anything said:
Is it GM? If so does it have a distibuter?

No, yes.

I can fix anything said:
pop off the cap feel the large amount of play in the distributer gear. Replace dist. both codes gone. That was too easy. Lets do a p0420 with no info

That COULD be part of a trouble tree. ALTHOUGH, just like the haynes manual, you never told me what to do if it passes. :dunno:

I didn't know either, so I replaced it "just to be on the safe side.

Now I've r&r'ed it twice, paid for a sensor, and a new dizzy assembly and am still at square 1. I don't have any info or guidance.

I'm not sure if I have it stabbed in exactly correct either. Can't check my timing, so can't tell.

richfinn · May 23, 2011

This basic code reader only gives you the numerical code? no mode$6? or live data?

Have you witnessed the misfire? is it permanent or intermittent? has the coil not cured it?

p0300 means random cylinder misfire?

p0340 means cam sensor range/performance defect?

Does it have an extended crank time?

diesel research · May 23, 2011

richfinn said:
This basic code reader only gives you the numerical code? no mode$6? or live data?

Have you witnessed the misfire? is it permanent or intermittent? has the coil not cured it?

p0300 means random cylinder misfire?

p0340 means cam sensor range/performance defect?

Does it have an extended crank time?

Yes, this is your average $50 5 digit reader. No definitions or text. P_ _ _ _
Yes that is the general consensus of the codes.
It does seem to have a little miss, sometimes hard to notice.
Extended crank occurs now and then. Think I should replace my fuel pump and starter?

Unfortunately when my mech replaced the coil, not only did it not fix the problem, I think it might be slightly worse. I took it back to him, and he said something about my bosch spark plugs causing the cam sensor problem, I think? He suggest I run champion, but I don't like champion, so I tried to do this on my own.

I can fix anything · May 23, 2011

Dear god put some plugs in it, then check connection at the mass air flow. and FP.

MrMark · May 23, 2011

Here's what I would do:

1) I would find out the code definitions and check underhood for obvious problems;
2) I would search the car forums online for my particular car to see if there are any obvious problems on that model and with that code;
3) I would be pretty limited now because I have no live data or fuel trims but with symptomatic diagnosis? you can take a few cracks at likely issues;
4) I would also work through the factory manual; not some **** like Haynes.

If all this failed I would take it to the Benz dealer and tell them to scope the cam sensor and run Star Mark on it and tell me what is wrong. $100 dollars is money well spent if you don't have the equipment.

I'm afraid on this one you need to scope the cam sensor to be sure it is a problem.

My uncle Joe said my Bosch plugs were causing misfire; Mercedes don't like Bosch plugs. On seond thought this is probably it. Bosch plugs.

richfinn · May 23, 2011

diesel research said:
Yes, this is your average $50 5 digit reader. No definitions or text. P_ _ _ _
Yes that is the general consensus of the codes.
It does seem to have a little miss, sometimes hard to notice.
Extended crank occurs now and then. Think I should replace my fuel pump and starter?

Unfortunately when my mech replaced the coil, not only did it not fix the problem, I think it might be slightly worse. I took it back to him, and he said something about my bosch spark plugs causing the cam sensor problem, I think? He suggest I run champion, but I don't like champion, so I tried to do this on my own.

How many miles has the car done?

How long have the German spark plugs been in the engine?

richfinn · May 23, 2011

I think the floats and choke bit is quite amusing

Stick · May 23, 2011

Again, I believe I see what diesel research is getting at. The responses have been somewhat insightful, but I think most of you might be on the wrong track.

Personally, I'd charge the battery and once that's done have it checked out, and run a charging system test on it (check for A/C ripple, proper voltage output, etc). I'd take care of that before I worry about any codes, wrong plugs, etc.

MrMark · May 23, 2011

I'd put my power probe III in the CAN com link on DLC and turn it on full blast and see what I got.

diesel research · May 23, 2011

richfinn said:
I think the floats and choke bit is quite amusing

Honest to god, my junk homeowners manual says this. I know for sure on a carburetor those could be legit. I'm not sure if you guys have haynes in england or I mean something similar.

richfinn said:
How many miles has the car done?

How long have the German spark plugs been in the engine?

190,000. 20,000.

I can fix anything said:
Dear god put some plugs in it, then check connection at the mass air flow. and FP.

It is speed-density.

MrMark said:
Here's what I would do:

1) I would find out the code definitions and check underhood for obvious problems;
2) I would search the car forums online for my particular car to see if there are any obvious problems on that model and with that code;
3) I would be pretty limited now because I have no live data or fuel trims but with symptomatic diagnosis? you can take a few cracks at likely issues;
4) I would also work through the factory manual; not some **** like Haynes.

If all this failed I would take it to the Benz dealer and tell them to scope the cam sensor and run Star Mark on it and tell me what is wrong. $100 dollars is money well spent if you don't have the equipment.

I'm afraid on this one you need to scope the cam sensor to be sure it is a problem.

My uncle Joe said my Bosch plugs were causing misfire; Mercedes don't like Bosch plugs. On seond thought this is probably it. Bosch plugs.

I like this somewhat. Unfortunately, why would I pay $150 for the manual/power train books, if I am only willing to spend $50-$70 for a no-frills autozone type pocket reader?

I like the online search but it has some problems, like suggestions to replace all kinds of parts, I have already spent more than a nicer scan tool would have cost. Granted, even that alone might not get me where I need to be.

Are you suggesting I take any make/model to MB because their scope is better?

LOL on power probing the CAN link! :lol:

Stick said:
Again, I believe I see what diesel research is getting at. The responses have been somewhat insightful, but I think most of you might be on the wrong track.

Personally, I'd charge the battery and once that's done have it checked out, and run a charging system test on it (check for A/C ripple, proper voltage output, etc). I'd take care of that before I worry about any codes, wrong plugs, etc.

This is a GREAT suggestion, but you should explain why? and if you would do this with every car or only certain symptoms or codes?

In REAL LIFE the above actually was a problem once. Cranks-No start. Cranking voltage about 10.7 volts. Starter motor spinning over healthy. Advanced symptoms were weak spark. I wasn't there in person, I was talking my brother over the phone. He observed weak orange spark with the home owner type spark tester.

A lot of head scratching to figure out troubleshooting methods since he had no codes to work off of, and no diagnostic tools.

Told him to put the battery on a charger since he ran it down trying to crank so long. He calls back and told me the prob was fixed and runs like a champ.

What happened? Battery charger began to charge, quickly showed charge, but then dropped back and refused to charge. A load tester had showed damaged cells. Well doesn't say damaged cell, but with the reduced voltage and cca it is safe to assume. Found out later there was enough voltage to fire starter, but system depends on a very healthy battery in order to produce proper spark under compression.

_______________________________

That said, a batt won't fix everyones problems, so I am still looking for these so called DIY trouble shooting techniques.

There are still a few things left I could do easily and they are not model specific, they pertain to all hall effect/distributor type vehicles.

diesel research · May 23, 2011

So far this thing has proven to be pretty useless.

The only use mentioned so far was to speed up visual inspections.

Other than that, it has caused a laundry list of ****:
replace sensor
replace dizzy assembly
replace sparkplugs
replace motor mounts
replace coil
*one mention of repairing harness, but this tool doesn't tell me if the harness is good or bad or what to repair.

__________________________

I do wiring harness repair EVERY day (that I work). Very often, the damage is visual. Clean cut, broken pin, green gobblins, ect ect. BUT sometimes there is absolutely no visual clue. Then what?

I am trying to find out how some people justify these things as DIYers. Seems only the most experienced pros can get away with these tools.

If anyone else wants to explain how to use the clues this code reader gives, feel free to take a stab at it.

richfinn · May 23, 2011

We do have Haynes manuals in Europe

I suppose the only advantage of this cheap code reader your using (rather than nothing at all) is that you can pretty quickly rule out stuff like broken primary ignition wiring/injector wiring and since its not thrown any fuel trim codes you could assume the fuelling is OK (sort of).

At this point of the diagnosis with 200,000 mls and the extended cranking symptom
I would guess that the cam sensor code might be worth investigating further. I would probably clear the codes and drive the car a while to see if they return just to make sure they are both hard faults.

If they did return, I would probably check the cam chain/belt for stretching to see if its messed up the timing.

Reading between the lines though, the fact that you only have a DVOM and a test light and you do lots of electrical wiring repairs tells me its going to be an electrical fault with the sensor or its wiring.

ourkid2000 · May 23, 2011

Great thread! Lovin it

richfinn · May 23, 2011

I sometimes use one of these types of Code readers on a particular type of Renault engine that suffers with COP failures very regularly, I carry the parts and it takes about 2 minutes to swap one coil. If I know the relevant DTC (p0304 for example) I can verify the fault very quickly and fix the car. These engines have no 1 cylinder located at the flywheel end of the engine and I have seen techs swap the wrong end and still have the misfire so I suppose there is some limited value to them if you know your way round a particular fault and just use it as a quick test. On this same engine EOBD (our version of OBD2) wont flag a crank sensor code so if i get a none start I always use the better scan tool that will do manufacturers codes.

richfinn · May 23, 2011

Im pretty sure you could test the output of the Hall sensor (cam sensor) in the dizzy with both a test light or a volt-meter its just an on/off digital signal if you confirm the reference voltage and the ground pin your just looking for a nice clean on/off voltage at the signal pin.

I suppose it could flag a performance code even if it open circuit or shorted.

diesel research · May 23, 2011

richfinn said:
Reading between the lines though, the fact that you only have a DVOM and a test light and you do lots of electrical wiring repairs tells me its going to be an electrical fault with the sensor or its wiring.

No, no, no. Forget about the fact I mentioned doing wiring repairs at work. I am not just using a test light lol.

For this scenario, I am average-joe, and only have those 2 things. This is a simulation. There isn't necessarily right or wrong answers. Some are definitely more wrong than others.

Moving on, let's talk about the rest of what you mention:

At this point of the diagnosis with 200,000 mls and the extended cranking symptom
I would guess that the cam sensor code might be worth investigating further. I would probably clear the codes and drive the car a while to see if they return just to make sure they are both hard faults.

If they did return, I would probably check the cam chain/belt for stretching to see if its messed up the timing.

Yes, so it's possible. You say investigate more on cps code. Give me some clues on how to do so.

Yes clearing codes is sometimes valid BUT often not. Glad you brought up this point. If I clear codes, I also lose valuable freeze frame data and pending counters. Also given the fact it seems to still occur, clearing codes isn't going to accomplish much.

Keeping in mind that misfires can go undetected by ear, and the fact after 200,000 miles, I am prone to not even notice some slight misses. A lot of owners don't. Plus, as a owner, I am "biased" into trying to believe nothing is wrong, because if something is wrong, it cost money out of MY pocket. There is a different psychology when you are spending money vs making money on car repairs.

Then you mentioned timing chain/belt. This particular make uses a chain. I don't want to pull all the FAD off (including mechanical fan) just for an inspection. Another DIYer bias (extra work w/o pay). Can you walk me through something easier?

We also cannot rule out other failures, they can easily be coincidentally happening at the same time.
________________________

Your use for swapping around parts definitely has validity. Not in this case, but in many other vehicles.

________________________

Some are probably confused on why this is in the tool section, but I do feel I am discussing how to use a tool, not how to fix a specific vehicle.

Stick · May 23, 2011

Believe me, a test light or meter is nowhere near fast enough to check for clean switching.

richfinn · May 23, 2011

diesel research said:
No, no, no. Forget about the fact I mentioned doing wiring repairs at work. I am not just using a test light lol.

For this scenario, I am average-joe, and only have those 2 things. This is a simulation. There isn't necessarily right or wrong answers. Some are definitely more wrong than others.

Moving on, let's talk about the rest of what you mention:

Yes, so it's possible. You say investigate more on cps code. Give me some clues on how to do so.

Yes clearing codes is sometimes valid BUT often not. Glad you brought up this point. If I clear codes, I also lose valuable freeze frame data and pending counters. Also given the fact it seems to still occur, clearing codes isn't going to accomplish much.

Keeping in mind that misfires can go undetected by ear, and the fact after 200,000 miles, I am prone to not even notice some slight misses. A lot of owners don't. Plus, as a owner, I am "biased" into trying to believe nothing is wrong, because if something is wrong, it cost money out of MY pocket. There is a different psychology when you are spending money vs making money on car repairs.

Then you mentioned timing chain/belt. This particular make uses a chain. I don't want to pull all the FAD off (including mechanical fan) just for an inspection. Another DIYer bias (extra work w/o pay). Can you walk me through something easier?

We also cannot rule out other failures, they can easily be coincidentally happening at the same time.
________________________

Your use for swapping around parts definitely has validity. Not in this case, but in many other vehicles.

________________________

Some are probably confused on why this is in the tool section, but I do feel I am discussing how to use a tool, not how to fix a specific vehicle.

Hey your cheapo code reader doesn,t do freeze frame or mode$06. Thats why its a valid DIY,er test

diesel research · May 23, 2011

richfinn said:
Im pretty sure you could test the output of the Hall sensor (cam sensor) in the dizzy with both a test light or a volt-meter its just an on/off digital signal if you confirm the reference voltage and the ground pin your just looking for a nice clean on/off voltage at the signal pin.

I suppose it could flag a performance code even if it open circuit or shorted.

Very good addition to the topic. Understanding sensors/waveform types could definitely be helpful. Although probably a vast majority don't know what a variable-reluctance, optical, or hall effect speed sensor is, let alone what a waveform is, or what type produces what type.

My crappy haynes manual does identify the 3 wires and their various positions. Hall effect is an on/off switch, although I'm not sure I would want to draw current of a bulb through the tiny switch.

diesel research · May 23, 2011

richfinn said:
Hey your cheapo code reader doesn,t do freeze frame or mode$06. Thats why its a valid DIY,er test

I'm loosing data that other people may need.

(if I throw in the towel and take it to someone else right after clearing codes, perhaps it is intermittent?)

richfinn · May 23, 2011

Stick said:
Believe me, a test light or meter is nowhere near fast enough to check for clean switching.

Better than nothing if you dont have a scope

diesel research · May 23, 2011

Stick said:
Believe me, a test light or meter is nowhere near fast enough to check for clean switching.

Agree, you would just have a skewed average number, maybe 3 volts maybe more, maybe less.

Since this vehicle uses standard 5v reference for the most part, this is another reason not to use test light. Even if sensor/pcm was robust enough to handle the current, the light probably wouldn't be bright enough.

Not sure if this vehicle has a pulse for every cylinder or just #1, but assuming it's just number one, we are talking about #1 coming around atleast 15x/second.

I MIGHT be able to slow the engine down by turning by hand. That could get a bit tedious, and is not a go/no-go test. Could potentially find a failure, but a pass does not mean sensor/wiring is good at all speeds/conditions.

I could try heating/wiggling harness while turning by hand, to increase chances of catching it in the act of acting up, but again, a pass does NOT equal success, only means continue on with more advanced testing.

It may even be possible to simulate a shutter wheel with a metallic object like flat tip screw driver, but again, I can only capture failures, not confirm good parts.

"Guilty until proven innocent" might be one philosophy, if sensor passes initial testing. On the other hand, before replacing, you would have to switch to "innocent until proven guilty" if you did not find faults. Of course, there are many other points of potential failure, so that is not all inclusive either.

richfinn · May 23, 2011

What kind of test lights do you use over there?

BlindViper · May 23, 2011

I got p1246 and p1247 which are related to the needle lift sensor in my vw tdi. I ohm'd the sensor and it was open. I tapped the sensor and the closed. This told me the sensor was bad and the harness for the car was not at fault.

MattT · May 23, 2011

Searching Year Make Model P**** is a good start. It won't diagnose a fault but usually gives you a starting point on the most common causes. If you're working on a rarer vehicle which shares a powertrain with a more popular one try searching both.

Getting factory documentation can be a big help. For the two OBDII Fords we own I bought factory shop manuals, wiring diagram books, and a factory powertrain manual on ebay for about the same price as two of the **** aftermarket manuals from a parts house.

Factory PDF manuals can sometimes be found for free download. I've found manuals for both the families Jeep products.

Worst case most all manufacturers now offer pay access to their factory documentation and the short term charges aren't that unreasonable.

http://www.nastf.org/i4a/pages/index.cfm?pageid=3291

Stick said:
Believe me, a test light or meter is nowhere near fast enough to check for clean switching.

If the DMM does frequency it can at least measure switching rate. Not a substitute for 'scope but better than nothing.

diesel research said:
Understanding sensors/waveform types could definitely be helpful. Although probably a vast majority don't know what a variable-reluctance, optical, or hall effect speed sensor is, let alone what a waveform is, or what type produces what type.

First step in correctly testing something is understanding how it works. Is the 4.9v you've got at a sensor low voltage or a 5v Vref?

richfinn · May 23, 2011

Im not really familiar with this engine, but it must be possible to check the valve timing without stripping the engine down.

Mr.Nutcase · May 23, 2011

Buy more tools, then fix, try to get info. Ask, Check TSB!!!!!!!!!!!!!!!!!!!

Why lose time, ask around, ie forums.
There are TSB that will adress DTC/....

richfinn · May 23, 2011

Find the timing marks in the Haynes manual its page 238 for the 99 model (hypothetically of course) and make sure the chain isnt stretched

diesel research · May 23, 2011

richfinn said:
What kind of test lights do you use over there?

The kind that have flashlight bulbs in them and 1 clamp. The probe completes the circuit. THEY ARE NOT COMPUTER SAFE.

A LED logic probe is safe for most applications and responds faster, but the average DIYer has never heard of a logic probe. They are also not the end-all solution, as they too have some limitations.

Remember, for this case I am "the average DIYer". Not the guy who chases lighting and ABS problems on loaded gasoline tanker trailers, or the guy who chases various degrees of electric fault on freightliner/detroit diesel combos. The test light is relatively safe on the trailers with such basic circuity. Even the 2 channel abs is safe and sometimes even the preferred tool. Obviously doesn't work on wheel speed sensors. Not a good idea for many things on todays road tractors either.

In the US, it is typical for the homeowner to have very little in line of diagnostic tools. He has his grandpas test light which used to be used to "diagnose" back in the days when voltage regulators were mechanical buzzing boxes. At some point in time, he may have caught on to a multimeter. It may not be high impedence, it may even be analog. It probably isn't true rms, and definitely isn't graphing. Quite likely to be manual ranging as well. These guys live (and die) by the continuity buzzer test/resistance test, and maybe source voltage test.

0705_mump_14_z+electric_fan_installation+test_light.jpg

diesel research · May 23, 2011

richfinn said:
Find the timing marks in the Haynes manual its page 238 for the 99 model (hypothetically of course) and make sure the chain isnt stretched

Tried that, there is no mention of timing marks for vehicles produced after 1986. There is also no mention of how to "lock out" timing.

BUT it is possible to rock the crank back and forth while watching the rotor, to measure backlash. Of course that is not mentioned anywhere.

As far as I know, valve timing is checked with a cam degree wheel. Kind of moot point since there is no specs as to how the cam was installed from the factory, to compare to.

Mr.Nutcase said:
Buy more tools, then fix, try to get info. Ask, Check TSB!!!!!!!!!!!!!!!!!!!

Why lose time, ask around, ie forums.
There are TSB that will adress DTC/....

Not so fast!!!!! A DIYer may not have access to a comprehensive TSB listing. Furthermore, there may not be a TSB for a failure that happens after 12yrs/200k miles....

Then there is this suggestion of buying more tools. I am the budget DIYer, not a professional. I am very stubborn and insistent that I do not need more tools. Secretly, I am a bit concerned I may not know how to use them. "Do't need that stuff, I'm not a pro, don't work on cars for a living, just need to get back on the road/pass inspection/or...:"

And finally. No, asking around on the internet is not necessarily the best option and I have proven that it may not save time nor money.

Using internet suggestions has resulted in replacing:
6 spark plugs
distributor removal twice (tedious labor only)
1 distributor assembly part
1 cps
1 coil pack

That's a lot of parts and labor. :beer:

richfinn · May 23, 2011

diesel research said:
The kind that have flashlight bulbs in them and 1 clamp. The probe completes the circuit. THEY ARE NOT COMPUTER SAFE.

A LED logic probe is safe for most applications and responds faster, but the average DIYer has never heard of a logic probe. They are also not the end-all solution, as they too have some limitations.

Remember, for this case I am "the average DIYer". Not the guy who chases lighting and ABS problems on loaded gasoline tanker trailers, or the guy who chases various degrees of electric fault on freightliner/detroit diesel combos. The test light is relatively safe on the trailers with such basic circuity. Even the 2 channel abs is safe and sometimes even the preferred tool. Obviously doesn't work on wheel speed sensors. Not a good idea for many things on todays road tractors either.

In the US, it is typical for the homeowner to have very little in line of diagnostic tools. He has his grandpas test light which used to be used to "diagnose" back in the days when voltage regulators were mechanical buzzing boxes. At some point in time, he may have caught on to a multimeter. It may not be high impedence, it may even be analog. It probably isn't true rms, and definitely isn't graphing. Quite likely to be manual ranging as well. These guys live (and die) by the continuity buzzer test/resistance test, and maybe source voltage test.

I think maybe its different over here, you get your Land Rover/Austin guys with an old test prod and a bulb holder, but anything from 95 onwards is so crammed in and full of electronics you would at least have an LED test lamp.

I just got back from Florida and its very different, I was expecting lots of Audis and Hondas but I was shocked just how many GM cars/Trucks you have over there, and they sell tyres and filters at the local ASDA supermarkets :shocking:

.

richfinn · May 23, 2011

Its not a regular rythmic misfire you can pinpoint to one bank of cylinders then?

Does it seem to shift around when the motor idles?

Can someone walk me through the procedures?

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