Archived 97 12v Scan says Engine not running

[Cooperman]

I had posted below that my 97 12v has the gen light on, and the alternator will not put out more that 11v. Two new batteries, and two new alternators in this last week. Batteries will charge to 13. 5 volts and hold.



I got a scanner, and the scanner cannot detect the engine is running.



Alt will put out 14. 6 volts when off the truck.



The scanner does not detect any codes, just says Engine Not Running.



Any guess where the problem is?

 

[Moe]

Try checking the engine speed sensor. If it cant "see" the crank turning, then it thinks the engine isnt running, Moe

 

[Cooperman]

Thanks Moe, I am beginning to think that may the the problem, BUT, I have both Tach and Speedo. If the sensor were not working, I don't think the tach would be working either... ... , I could be wrong there.



I tried disconnecting the intake air heater relays, and that did nothing either.



Everything is working on the truck except alternator output voltage. I am really thinking I may have a problem PCM. Hate to just buy one to test.....



Again, thanks Moe. Further comments are encouraged, even along the previous thoughts. Ron

 

[AOwens]

I had a speed sensor bad and had tach and speedo both working. The truck had an external regulator on it until the speed sensor was replaced during a trans rebuild.

 

[Cooperman]

AOwens - thanks for the reply. I am getting a bit confused here. A "speed sensor" from the transmission (yours was corrected on a tran rebuild) should indicate rolling speed. I believe (correct me if I am wrong) that my "speed sensor" is on the diff.



I get the "engine not running" whether rolling or stopped, so I don't think it is really a "speed" issue, but an engine running issue, which would involve the crank position sensor above the harmonic ballancer. If that is incorrect, let me know.



I fear running down the "replace things until it works" path. That could get expensive.



Thanks - Ron

 

[Sticks]

Yeah, something is not sending a signal to the PCM, or the signal got severed.

Check your connections.