ECM codes

[vilant]

Anyone know which ECM malfunction codes turn on the Check Engine Light? I looked in the FSM and it gives the # and what it refers to. But I don't see which, out of the 30 codes, actually turn the CEL on. Do all ECM malfunction codes turn on the CEL? Or none at all? Is there a list of which ones do and don't, somewhere in the FSM that I missed? TIA:cheers:

[tccrab]

Pretty sure pretty much all ECU codes will trigger the CIL.

CCM, BCM (ABS, AC, etc) codes don't trigger CIL.

'Crabs

[vilant]

Thanks, Tom. I should of put SES instead of CEL. But you got the idea. I just think it's strange a few of them do, like #52 low oil temp or #15 low coolant temp.

[Hib Halverson]

I think, if you read the diagnosis info for those DTCs, the codes set when the ECT or the oil temp sensors are sending an impossible signal, ie: ECT below -26°F degrees when the engine is running or engine running for more than 30 minutes and oil temp below -36°F.

Either of those sensor signals would indicate a problem with the sensor or wiring so...the ECM turns on the MIL.

[Schrade]

Some diagnostics flow charts DO ask if there's a SES light lit up in the DIC, but which ones they are, escapes me at the moment...

And they can 'go away', if a few Closed Loop cycles pass without some circuit being called upon to check for spec parameters. EVAP Purge command might be one...

[vilant]

I think, if you read the diagnosis info for those DTCs, the codes set when the ECT or the oil temp sensors are sending an impossible signal, ie: ECT below -26°F degrees when the engine is running or engine running for more than 30 minutes and oil temp below -36°F.

Either of those sensor signals would indicate a problem with the sensor or wiring so...the ECM turns on the MIL.
Ah, didn't think of that, good point.

[vilant]

Some diagnostics flow charts DO ask if there's a SES light lit up in the DIC, but which ones they are, escapes me at the moment...

And they can 'go away', if a few Closed Loop cycles pass without some circuit being called upon to check for spec parameters. EVAP Purge command might be one...
There's definitly codes that get stored. When I took mine in to get inspected, I asked the mechanic to see if there was any codes. There was a slew of them, but the SES was never on. Like you say, the light was probably on, then the problem either went away or the PO had it fixed, but never cleared the codes.

[Hib Halverson]

If codes were stored but the light was off, either they were history codes or there's a problem somewhere with the MIL.

When you key up but don't start the engine does the MIL come on during bulb check?