Vehicle computer

dodge

#1

About 15 months ago the computer was replaced on my 1999 Dodge Ram Pickup. (Truck would stall in traffic, and would turn over but not crank.) Two months later, we took it back to repair shop with same symptoms. The mechanic said it was the battery, which was replaced. I had no more problems until about 3 weeks ago. It wouldn’t crank even with a jump, and I noticed the gas gauge wouldn’t register even though tank was half full. I took it to a different mechanic, who said it was the computer (and he noticed I had a fairly new one in there). Computer was replaced and guess what…same symptoms happened two days ago; mechanic just called and said he’ll do more checking but it’s possibly the computer again (which is under warranty). He seems confused what keeps causing this. Can you shed some light?


#2

NanaNoel, one clarification. “Turn over” and “crank” mean the same thing, ie the starter is making the engine turn, before the engine actually starts. So if an engine “turns over,” by definition, it’s cranking.

You said when you took it back to the mechanic, it “wouldn’t even crank with a jump.” I think you mean it would crank (the starter would make the engine turn) but the engine would not start. Is that right?

Some possibilities: faulty fuel pump, or faulty crankshaft position sensor. Either of these can cause intermittent stalling/no start conditions. A mechanic can check fuel pressure when it won’t start. If fuel pressure is good, I would try replacing the crankshaft position sensor.

The fact tht the mechanic thought it was a bad computer makes me suspect the crankshaft position sensor most. A bad sensor will cause the computer to shut down the engine, and lead to the mistaken assumption that the computer itself is bad.


#3

I would be looking for bad wiring someplace like the battery cables or grounds from the engine to the firewall. Someone would have to explain to me pretty clearly how a bad computer could cause a no cranking sympton (starter motor not running) or gauge not registering. It could cause a no start but not a no crank. I’ve never had a bad computer in 1 million miles but I did carry a spare and swapped them once in a while for trouble shooting. Having three bad computers would seem pretty far fetched.


#4

On failure to crank, the first test I do after visual inspection & cleaning and tightening battery posts is to probe the voltages on both terminals of the starter motor during attempted cranking (i.e. key in “start”). If both are above 10.5 volts, that usually means the starter is bad. If either is below 10.5 volts, then I work backwards to find out why.

I think before I replaced the computer again, I’d find out why the gas gauge isn’t working. That could be an important clue. There may be a bad connection or connector and the gas gauge is on that same connector.


#5

There is no diagnostic information in your post as to what is missing during the no start.

Example:

No spark
No fuel pressure
No injector pulse
No RPM on scan tool
No network communication

Also which engine is it and how many miles?


#6

Yes, engine would not start. Truck has over 100,000 miles. Thanks for suggestions.


#7

It was the crankshaft position sensor - thanks to all!!


#8

@NanaNoel‌

Congratulations!

By the way, I would consider going back to the last shop that replaced the computer and explaining that it was in fact the crank sensor, and not the computer, which fixed the problem.

I would politely ask them to reimburse you.

The worst thing they can do is say no

If they say no, ask them to at least give you store credit . . . perhaps the next tune up will be on the house


#9

Curious, is the gas gauge working now? I’m not aware of any logical connection between the gas gauge and the crank sensor.