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txchevy
New User
Aug 24, 2009, 8:32 AM
Post #1 of 3
(1949 views)
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Intermittent MIL Warning
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Hello,
I have a 2001 Chevy Blazer (4wd, automatic). It just failed the state safety inspection because the "check engine soon" lamp didn't come on while turning the key (but not going so far as to start the engine). I checked all the fuses inside the dash, and they all looked fine. While I was doing this, I noticed the MIL lamp did come on while turning the key to the middle position. I began to think the tech was seeing things (or not seeing things), but then I figured this out--if the car sets for a while, the MIL will appear while semi-turning the key. If you then start the engine, stop the engine, and then try to semi-turn the key (apologies for not knowing the right term), the MIL fails to appear.
Any thoughts on what could be causing this? The lamp bulb isn't the issue, as it does light up if the engine hasn't been started recently. Also, the tech said there aren't any problem codes registering on the vehicle.
Thanks for any thoughts!
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txchevy
New User
Aug 24, 2009, 9:59 AM
Post #2 of 3
(1929 views)
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Re: Intermittent MIL Warning
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UPDATE: I have more details.
If you start the car, then shut it off, and then partially turn the key on (no engine) in less that 8 seconds, no (test) MIL light appears.
If you wait for 8 seconds or more after starting the car, the MIL test light turns on with a partial (non-engine starting) turn of the key.
Is this helpful?
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DanD
Veteran
/ Moderator
Aug 30, 2009, 11:12 PM
Post #3 of 3
(1901 views)
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Re: Intermittent MIL Warning
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The times that you can get the MIL to come on; will it stay on or does it come on for one or two seconds and then shut off?
If it just comes on and then shuts off; that’s the bulb check for the instrument cluster; all warning lights in the cluster should do this. The bulb(s) check should happen every time you turn the ignition too the run position; that’s after the ignition has been off long enough for the memory of the cluster too completely shut down; likely your 8 seconds.
The MIL should blink off at the end of the bulb check and then come back on; if the ignition switch is left in the run position, engine off.
The MIL light, after the bulb check is controlled by the VCM/PCM (engine management computer). The easiest way to test the circuit; would be with a scan tool commanding the VCM to turn on the MIL. If the VCM doesn’t or cannot turn on the light; you would then have to find out whether it is a wiring issue between the VCM and instrument cluster, whether the light driver (switch) inside the VCM has lost the ability to ground the circuit or the instrument cluster has an internal issue not allowing the light to come on when requested by the VCM.
To test all of this would mean a good working knowledge of the system, accurate wiring diagram(s) and test equipment; ie scan tool and digital multi-meter.
Dan.
Canadian "EH"
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