"Service engine" light not coming ON

'97 Blazer s10.

As far as I can see, everyone else has trouble getting them to go off. Mine doesn't come ON reliably at start-up, and so it fails the state emissions test.

Was just found today at inspection. The light comes on the first time the key is turned, then goes off after engine has started. But then the tech turns off the engine, and turns the key again. No light comes on, and the light won't come on again until the key is left unturned for a minute or so. Then it comes on one time, but not on repeated turns of the key.

No DTC is set.

I have the service manual, but unfortunately the diagnosis of this problem is in the "Driveability and Emissions Manual," which I have never seen or heard of.

The vehicle runs fine. Any ideas if this problem could be in the ignition switch? The PCM? The VCM?

That may be normal.
I have saw some cars and trucks do that.
Un plug a sensor like eng tempt or air tempt sensor and see if it will turn on the light.
If so everything is working good.
Let us know how unpluging a sensor goes.

Thanks MT. I will try it now and let you know.

I asked the guys at the inspection station though, and they agreed they'd never seen it before. At the same time though, they had no idea how to fix it, so I didn't feel they were trying to repair something not broken.

If they are just fliping the key off and then rught back on that is improper testing.

There is a wait peroid after turning key o before turning it back on..
Like wait a few minutes with the key off before turning back on for bulb check.

Repair book says wait 15 seconds or more.
But
Give it a minute or two for a slower time out one.

Tell the inspection station to not get so fast on the trigger.
Wait a couple of minutes and the try it.
Let us know how it goes.
Good Luck

Whoops. Just thought of something. If I disconnect a sensor and set a trouble code, then the code will still be there when I take it back for re-inspection. That is an automatic failure, until the code resets itself. I have a scan tool, and I can re-set it, but then I need to drive 150 miles for enough data to collect so I can pass the inspection. Not much of a problem except I'd have to do it all in the next week, because my sticker expires on Dec 31.

But even if I do that, how do I prove to the inspectors that nothing's wrong?

MT--didn't see your last post before I posted my last.

I might have to try a different inspection station, though I think they have a computerized record of today's failure.

Yes if you set a code and the clear it you have big wait peroid for everything to reset.

Try explaing it to them about the wait peroid.
Or getting ahold of the main big boss.

If they have a good scanner capable of turning the check engine light on for test they should be able to test the check engine light to see if it is working or turning on OK.

If no codes are set and the check engine light comes on for the first key on bulb test and then goes off after a normal start up it should pass.

That should all that is required for inspection.

Good luck and let us know how it goes.

Here's what I tried, using my watch:

1st Turn of key--MIL comes on, and will continue to come on when the key is turned, on/off without starting the engine, indefinitely.

After engine starts, light goes off. Then if I shut off motor and again turn key within 5 seconds or less, the MIL will not come on, though all other dash lights do.

If wait more than 5 seconds before turning key, the MIL again lights up appropriately.

It happens this way exactly the same, each time. 5 seconds seems to be the required interval.

So this probably is a normal result. Why techs who do this for a living don't know about it, I have no idea.

Hard part will be proving it to them.

Here's what I tried, using my watch:

1st Turn of key--MIL comes on, and will continue to come on when the key is turned, on/off without starting the engine, indefinitely.

After engine starts, light goes off. Then if I shut off motor and again turn key within 5 seconds or less, the MIL will not come on, though all other dash lights do.

If wait more than 5 seconds before turning key, the MIL again lights up appropriately.

It happens this way exactly the same, each time. 5 seconds seems to be the required interval.

So this probably is a normal result. Why techs who do this for a living don't know about it, I have no idea.

Hard part will be proving it to them.

Good luck on that end.
If they get to stubborn on the deal ask them to look it up in the repair manual.
The good factory repair manuals say to wait 15 seconds before turning key back on when checking/testing it.

Let us know how it goes.

Thanks MT. I'll let you know.

Most states with emission testing have a referee or complaint number on the testing notice. Call them, on your cell phone from the testing station, if need be. Sounds like the light test is a visual "check off" test and the techs may be doing it wrong.

If you clear the DTC's and need to force the monitors to run and complete their tests, here is the drive cycle. With a little practice, you can do it in about 20 minutes.

http://www.obdii.com/drivecycle.html

Thanks for all the advice everyone. I found in the service manual that a 15 second wait is required after shutting off the engine before testing obd2.

Took the manual to the inspection station, and they made a bunch of comments about it all had to "be new" (though the vehicle was made in 1997), and passed the inspection.

Thanks for all the advice everyone. I found in the service manual that a 15 second wait is required after shutting off the engine before testing obd2.

Took the manual to the inspection station, and they made a bunch of comments about it all had to "be new" (though the vehicle was made in 1997), and passed the inspection.


You are welcome and thanks for posting back how it went.

Glad you got it threw there heads.:lol2: :grinyes:
Good luck