What the???

[jaybee]

Today I'm troubleshooting my son't '91 Lumina (yes, I'm still having trouble with it).  It finally stored a trouble code 42.  A mechanic friend printed out the procedure for tracing this code and it should have been pretty straightforward...but of course nothing is.

Here's my question.  The chart says to probe a connection on the ECM harness with a test light.  It lights then 'A'.  It doesn't then 'B' according to the flow chart.  Umm, what if it barely glows?  I'm assuming that should be counted as 'it lights', but what else does it tell me?  Could a failure in the ignition module I'm testing lead to a weak current leak?  Doesn't sound like a normal failure mode for electronic parts, most commonly solid state electronics are either all or nothing (although sometimes all or nothing comes and goes).  Maybe a wire with an insulation breach that is trying to short but not quite getting the job done at the moment?

[oiler]

If I had a Lumina manual at home I could tell you exactly what you should see by tracing the schematic but I can't do that till tomorrow.
However with GM flow charts when they say lighted they mean lighted.
If the test light only glows that is assumed to be off.
Code 42 should be a EST failure right?
EST codes have always been a * to diagnose, specially on 3.1s and 2.8s
Almost always a module though, rarely a ECM.
If you need more info I can check a manual at work tomorrow
Jeff

[model a vette]

What are the symptoms?
As stated above Code 42 is usually a bad module. They CAN fail slowly. They will sometimes work and then shut off. Usually they will get worse. The first one I had that went bad shut off when hot. If it cooled down it would work for a while then shut down again.
My code chart says bad results of diagnostic is bad EST module 3 times and 4th bad is ECM (computer).
My bet would be bad EST.
My manual refers to using an ohm meter for most of the tests.

[jeffa]

In my limited knowledge of these (I have owned a "Commodore" GM 3.8 V6, 2000 model for two years and have never had anything go wrong. But, I am an electronics tech (35 years) and as usual, I am very interested in making these things give their best, and also be fore-armed in case of failure.
I'd be checking grounding. On the car I have, there are some well-known trouble spots for grounding failures, but I'd guess you car would be different in that respect.
1: Have you got a 12volt indicator? Is it low current? (You are not using a high current bulb for example?).
2: Can you measure the high's and low's with a high-impedance multi-meter?
3: Ground the ECM. Check via the circuit diagram (if you can get one) where the ground path/s are and make sure they go where they should. If the ECm doesn't have a good ground, it will try via any path it can, maybe via other sensors etc and give you the glowing bulb you mention.
3: Make sure the engine is properly grounded to the body and to the ECM.

I'd be tracing the glowing test lamp first.