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Ok so this one has really stumped me. I’m by no means an expert but I like wiring and understand it pretty well. I’ve also learned so much over the last few weeks from ScannerDanner, it’s amazing the knowledge he has.
Anyways, on to the problem. This 2003 Dodge 4.7 came into the shop probably 2 months ago because the owner said it would randomly shut off. He could pull over, put it in park, turn key off, and then turn it back on and it would start right up.
I hooked scan tool up and no codes. On the test drive it did exactly what he said it would. Under acceleration it will (sometimes) shut off and gear display acts crazy (I think it goes blank). You cannot bump it into neutral and start it. The key has to go all the way to the off position before it will restart. I can also replicate the issue with the truck in park and by snapping the throttle.
So what is happening is the pcm/tcm (all together on this one) is shutting down. Scanner looses com, 5v ref goes dead, and this is why there’s no codes. I have checked power and ground going to computer and all are steady when the truck dies. I have scoped cam and crank. When the truck dies sometimes the crank signal looked odd so I replaced that. Same thing. I have also replaced the pcm/tcm to no avail.
The problem does seem to get worse the hotter the truck gets. It will get so bad that before the truck even cranks up the computer shuts down.
One thing I forgot to mention is while scanning the trans data I found that the temp sensor read like 1000 degrees. I found the 5v ref wire going to the sensor and unplugged it but that did not change anything.
Thanks I’m advance for any advice.
Yes I can try that. I will have to look and see what all is on the 5v ref. Only issue is the problem could be in the transmission and there is no way to unplug some of those sensors because the computer freaks out lol.
I do think it is a sensor shorting out though, just can’t find which one.
One thing I didn’t mention is if the truck is running and I have my DMM hooked black to ground and then backprobe the 5v ref the truck will die. I have done the same on other vehicles and it makes no difference.
Also with the red lead on the positive cable and the back probing the sensor ground wire the voltage is erratic. I do not know if I can test sensor ground this way because it goes through the computer.
Thanks
Matt18 wrote: Also with the red lead on the positive cable and the back probing the sensor ground wire the voltage is erratic. I do not know if I can test sensor ground this way because it goes through the computer.
Thanks
Me personally I think you summed it up right there. So what's the average voltage reading on the sensor ground? Is it bouncing back and forth like it's open? Or does it slowly climb up in voltage? What does the same sensor ground look like at the pcm. There's too many variables for me to say... but my guess is you have high resistance on a computer ground or somewhere in between the sensor and computer. Exactly as you said, sensor ground goes thru the computer. Not sure exactly how you tested the powers and grounds at the pcm but it must be loaded. Anyways I told myself I wouldn't write a book since Paul already did. You need to get and read his book. It tells you EVERYTHING you need to know to troubleshoot this issue. Plus all his many videos on the 5v ref.
I will do some testing next week sometime hopefully, but thank you both for pointing me in the sensor ground direction. If I remember right, when testing the voltage would hold steady (around 12-14 volts) until I started messing with the throttle then it would drop off to around 3 even to 0 sometimes. I do believe I checked the sensor ground at the computer and it held steady. I will investigate more when I get time. I do think this is the direction to go. Thank you both for confirming.
