CEL on while cranking
This one I find very interesting…kind of backwards symptom to me but has to be an excellent clue and I expect someone out there knows immediately what it is. The vehicle came in as an intermittent crank no start. Didn't really act up for us but when I tested the battery it failed and then I experienced a crank no start. Changed the battery and it seems pretty consistent that when the battery is disconnected for awhile it will do the crank no start. I started observing the CEL light and found something quite interesting. Normally it comes on during bulb check and when cranking goes off and the car starts. When it cranks and doesn't start the CEL stays on during cranking and the second it turns off the vehicle starts. I guess I'm thinking internal PCM failure but would love to know that from someone who has dealt with this.
When it cranks but doesn’t start can you communicate with the PCM?
It is normal for this vehicle to crank no start after an ECM reset or battery replacement. The key is normally turned on for 20 seconds or so for the throttle to learn and whatever else happens and then it will start normally.
As Brandon said it is completely normal behavior for a battery disconnect or code clear to cause a crank no start. The PCM is relearning the throttle position. Turn the key in the on position for about 30 seconds after battery disconnect or MIL clear, then start the vehicle.
Norman, Imagine you are the computer. How do you know it is time to start, and shut of the MIL, begin to fire your injector-coils? Engine RPM, is my guess. This is just my guess. Lack of crank signal, or crank sync with cam signal. Fun fact, back in the 80's when you would flash codes out of a GM. If all was normal, you would get 12 12 12. I was told this meant there were no codes. That was…