check engine light function

[coppermouse]

A guy at work here claims the only purpose of the check engine light is to indicate a malfunction of the emissions system and to cover the manufacturers butts. I do not believe this is true is it? It can indicate non emissions problems can't it?

 

[pseudorealityx]

Of course.

EDIT: That said, almost any "normal" engine problem will also show up as an emissions problem as well. Misfires, AFM not reading, etc.

 

[gsport]

i think he's right... emission related problems, so pretty much anything that would effect the emission output

 

[Daedalus]

OBDII was standardized and mandated by the Clean Air Act (1990) and enforced by the EPA, so it's a given that emissions is the biggest driver. That said, there are a handful of codes that can be argued do not have much to do with emissions. There are also manufacturer-specific codes which can light the MIL, and which gives some freedom for manufacturers to create their own logic for reporting problems.

 

[torqueman2002]

The malfunction indicator lamp (MIL) or service engine soon (SES) light is for emission related faults. The service vehicle soon (SVS), if present, is for non-emission related faults.

Service Information
2009 Cadillac CTS | CTS (VIN D) Service Manual | Diagnostic Overview, Starting Point, and Programming | Vehicle Diagnostic Information | Diagnostic Information and Procedures | Document ID: 1800770
--------------------------------------------------------------------------------

Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Emissions Related DTCs
Action Taken When the DTC Sets - Type A
• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Action Taken When the DTC Sets - Type B
• The control module illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

• The following applies to misfire DTCs:

- If the control module detects a low level or an emission level misfire condition during 2 consecutive trips, the control module illuminates the MIL.

- If the control module detects a high level or catalyst damaging misfire, the control module flashes the MIL at a rate of once per second.

- If the control module detects a misfire during 2 non-consecutive trips, the stored conditions are compared with the current conditions. The control module illuminates the MIL when the following conditions occur:

• The engine load is within 20 percent of the previous test that failed.

• The engine speed is within 375 RPM of the previous test that failed.

• The engine coolant temperature is in the same range of the previous test that failed.

• The following applies to fuel trim DTCs:

- If the control module detects a fuel trim condition during 2 consecutive trips, the control module illuminates the MIL.

- If the control module detects a fuel trim condition during 2 non-consecutive trips, the stored conditions are compared with the current conditions. The control module illuminates the MIL when the following conditions occur:

• The engine load is within 20 percent of the previous test that failed.

• The engine speed is within 375 RPM of the previous test that failed.

• The engine coolant temperature is in the same range of the previous test that failed.

Conditions for Clearing the MIL/DTC - Type A or Type B
• The control module turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Non-Emissions Related DTCs
Action Taken When the DTC Sets - Type C
• The control module stores the DTC information into memory when the diagnostic runs and fails.

• The MIL will not illuminate.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.

• The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC - Type C
• A current DTC Last Test Failed clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.

• Clear the DTC with a scan tool.

Action Taken When the DTC Sets - Type D
• The control module will take default actions but no DTC will be stored in Failure Records.

• The MIL or SVS will not illuminate.

Conditions for Clearing the DTC - Type D
Clear the DTC with a scan tool.
© 2009 General Motors. All rights reserved.

 

[sberry]

I would say it depends on the car and age.

 

[gofastman]

OBDII was standardized and mandated by the Clean Air Act (1990) and enforced by the EPA, so it's a given that emissions is the biggest driver. That said, there are a handful of codes that can be argued do not have much to do with emissions. There are also manufacturer-specific codes which can light the MIL, and which gives some freedom for manufacturers to create their own logic for reporting problems.

^ what he said.
Slightly off topic, but if anyone brings up "OBD 0" while talking about check engine lights, round-house kick them in the teeth for being stupid

 

[Fiberglass Fred]

I agree with most of what's been said. 99.99% of the time it is about emissions, but I know some cars use that same light to alert the driver to non-emission problems as well.

I don't remember the make/model, but at one point there was a car that used the "check engine light" to indicate that it was low on oil. I think it was one of Honda's or Toyota's models in the early 90s, but I can't remember for sure. I wonder how many people ruined their engines thinking that it was just an O2 problem.

 

[e-tek]

I think the corrected term should be: Malfunction Indicator Lamp Functioner.....

or, ****!

 

[krusty the clown]

I would say it depends on the car and age.

I agree with most of what's been said. 99.99% of the time it is about emissions, but I know some cars use that same light to alert the driver to non-emission problems as well.

I don't remember the make/model, but at one point there was a car that used the "check engine light" to indicate that it was low on oil. I think it was one of Honda's or Toyota's models in the early 90s, but I can't remember for sure. I wonder how many people ruined their engines thinking that it was just an O2 problem.

kind of.........there were some older models where the over temp and low oil pressure warning lights were combined into a RED check engine light. but for all practical purposes a check engine light (amber) is for emmisions related failures. and yes an ign failure will be considered an emisions failure.

 

[gsport]

****!

..........

 

[timmytomas]

Im going to agree with him.

 

[dieseldodge01]

Mine told me my dash was on the fritz

 

[Old Bill]

My buddy's 2007 Ford Ranger had the light come on. reason? Gas cap was loose! True story.

 

[DarrenF]

My buddy's 2007 Ford Ranger had the light come on. reason? Gas cap was loose! True story.

This is VERY common

 

[ddawg16]

My buddy's 2007 Ford Ranger had the light come on. reason? Gas cap was loose! True story.

And the reason it does is because it means that the fuel vapors are now escaping into the air instead of being absorbed by the charcoal canister.....

BTW...My CEL starts flashing if the fuse to the ****** blows......nothing to do with emissions.....

 

[krusty the clown]

BTW...My CEL starts flashing if the fuse to the ****** blows......nothing to do with emissions.....

yes and no.........if the transmission isn't shifting properly it could be using more fuel hence more emissions. some models also flash the trans or OD light to indicate a trans problem AND the MIL to indicate there is a code stored in the PCM.

 

[Kevin54]

kind of.........there were some older models where the over temp and low oil pressure warning lights were combined into a RED check engine light. but for all practical purposes a check engine light (amber) is for emmisions related failures. and yes an ign failure will be considered an emisions failure.

.

So a CEL that the code says is for "Camshaft position sensor / Crankshaft position sensor correlation" (Can't remember the damn code at the moment) would be an emissions problem? What it is or what my nephew explained to me was the distributor gear is probably worn somewhat and now the crank / cam sensors cannot get exactly synchronized and is throwing a fault code. The light comes on periodically and lately has been on more than off. I'm just going to toss in a new distributor over the holiday shutdown next week.

I guess one can say it would be emission related but I would look at it more as electrical. Then again if the computer starts to adjust for the fault code it would change the emission output on the vehicle. BTW....it is a 2000 GMC Jimmy if anyone is interested in knowing what the vehicle was.

 

[krusty the clown]

.

So a CEL that the code says is for "Camshaft position sensor / Crankshaft position sensor correlation" (Can't remember the damn code at the moment) would be an emissions problem?

absoluely. the whole idea of the compuer control is to keep an engine "in tune" for reduced emmisions. if the computer can no longer adjust the timing correctly due to mechanical wear it will flag a code. i think some of you are confusing emission levels and emission components.