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sprinkles08
sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 23002
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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I have a 1994 Dodge Ram 2500 Cummins diesel, 5 speed manual

Customer Question

I have a 1994 Dodge Ram 2500 Cummins diesel, 5 speed manual transmission. The ECM quit working. Sent it off for repair. Installed, drove 3.5 miles and it quit again. Warranty covered this fix, but won't cover future repair for same issue. They rebuilt the 8V REF Circuit due to 2R OHM Resistor & Diode being blown. We have replaced the ESS (aka Crankshaft Position Sensor), the Speed Sensor in the rear differential and the Sensor that comes out of the transmission. Any ideas as to anything else that might cause this problem?
Submitted: 2 years ago.
Category: Dodge
Expert:  sprinkles08 replied 2 years ago.
Hello and welcome to JustAnswer!
It's hard to say if there was actually an issue on the truck or they simply returned the PCM in the same state you sent it to them in the first place. This type of company in general has shown very poor quality control and multiple repair attempts or multiple returned failed units is a normal situation.
The only two sensors that use the 8v reference are the crank sensor and the vehicle speed sensor on the trans. A short to power or ground on the 8v circuit will take the PCM down until the short is removed, but I've never seen one damaged by one of these shorts. I've never seen a case where a short actually caused damage, the PCM will always wake up as soon as the short is removed.
In any event, if something external actually damaged the 8v reference circuit inside the PCM then it was a short to power or ground on the 8v circuit (orange wire). The problem either had to be in one of the sensors already replaced or it's a wiring issue. The only thing you might consider doing besides replacing the sensors is hardwiring the circuit from the PCM to both sensors and cutting the old wire out of the circuit.
Customer: replied 2 years ago.
We installed the ECM this morning. The temperature gauge, oil pressure gauge, alternator charging gauge and tachometer are not working. They were working fine before. We didn't test drive it, so don't know if speedometer works or not. Checked all the fuses and they are good. Now what?
Expert:  sprinkles08 replied 2 years ago.
It's not actually charging and the a/c compressor won't engage, correct?
Customer: replied 2 years ago.
Not sure if it's charging. Sounded like the ac compressor engaged.
Expert:  sprinkles08 replied 2 years ago.
Can you check both?
Customer: replied 2 years ago.
Did test drive. AC blows hot air. Speedometer not working either. The fuel gauge is the only one that works.
Expert:  sprinkles08 replied 2 years ago.
Do you have a scan tool?
Customer: replied 2 years ago.
No
Expert:  sprinkles08 replied 2 years ago.
Do you have a digital voltmeter?
Customer: replied 2 years ago.
I do.
Expert:  sprinkles08 replied 2 years ago.
What is the voltage on the 8v reference wire and the black/light blue sensor ground wire?