Hey Guys, I've got a 1999 ram 2500 5.9 24V cummins with ~300k miles. I'm trying to determine whether my ECM is the cause of some problems. Here's what's happening and what I've done to troubleshoot. Any feedback is much appreciated! Thanks

Symptoms:

• Intermittent low power - truck starts and idles fine but sometimes has trouble getting power and getting up to speed. I checked my fuel pressure and I am getting ~15psi from my airdog at the VP44.
• Oil pressure gauge reads 0 psi - I have already tried two brand new oil sensors and neither one will read properly. I hooked up a mechanical gauge and I am getting ~70psi oil pressure at idle
• Water in fuel light is on - I don't use the factory fuel filter (since I have an airdog). I drained the factory filter, removed the WIF sensor for inspection, and cleaned it. reinstalled everything and WIF light still remains on.

Troubleshooting steps taken so far:

• Checked all fuses in engine compartment and cab - all okay
• checked all sensor connections (oil pressure, MAP) and main wiring harness connections - unplugged cleaned and plugged back in.
• Checked all ground connections on entire truck.
• Pressure tested from air intake to my manifold and holds pressure fine.
• Here's the main thing I've done that is making me suspect a bad ECM:I checked a wiring diagram and it looks like the MAP and oil sensor are fed through the engine mounted ECM. I checked the "unswitched +12v" supply wires on the ECM's 50pin connector and I am getting a good 12 volts out of those two wires. With the 50pin connector plugged into the ECM, I took readings from my oil pressure and MAP sensor connectors. Both of these connectors have a +5volt supply that goes to the sensors. I am only reading .4v at those supply wires going to the sensors. In other words, I've got the right +12v going into my ECM but I am only getting .4v (not the correct +5v) coming out of my ECM and going to the oil pressure and MAP sensors. Would this be a sign of a bad ECM?

 

Welcome to DTR

Do you get the CHECK GAUGES light on the dash while running because the oil pressure indication is 0?

The Dodge PCM controls the instument panel with the Wait to Start (WTS) light being an exception. That is driven by the Cummins ECM.

Any codes or check engine lights?
How is the WTS light operating? If that is acting funky, that is a sign that the ECM is acting up too.
Are you missing the +5 Volts at all sensors? Oil pressure, MAP, IAT, CPS. I can't think of where else the 5 Volt line goes to. Your troubleshooting technique is good!

 

Thanks! You're close to me. I am in Houston.

Yes I do get the check gauges light from the oil pressure reading 0.

My Wait to start light is working fine and has never given me any problems.

I was previously getting a P0237 code. I unplugged my MAP sensor connection, cleaned it, and reinstalled. I also removed the MAP sensor and cleaned and reinstalled. I plugged it all back up and still got the P0237 code so I used my OBDII to clear it and it hasn't come back since.

Other than that, I currently have no other DTC's.

I have only checked for the +5 volts on the MAP and oil sensors (since those were/are acting up). Based on the diagram I am looking at, the MAP, OIL, CRANK, CAM, and APP sensors have +5v supplies. The IAT does not appear to have a +5v supply. I will check the Crank, Cam, and APP sensors when I get home.

Anything else you can think of? Thanks for the help so far!

 

Found this in the service manual for the oil pressure sensor on the diesel engines:

From reading that, the ECM provides the +5 Volts, as well as it's own sensor ground. They (Cummins) likely did that to isolate the sensors from the trucks electrical system for signal noise prevention. What is interesting is that the PCM also has a +5 Volt system (2 actually, primary and secondary).

The manual is less descriptive on the operation of the IAT, MAP, and APPS sensors.

For the Malfunction Indicator Light (MIL), it will stay lit for as long as whatever triggered it is still faulted out. If the fault clears, the MIL light will remain lit for 3 trips. As long as that fault is still clear after 3 good trips, the light will turn off, but the code will be stored for up to 40 trips. Some codes are cleared after one or two trips (it didn't elaborate on which codes do that). So in your case, the P0237 code not clearing right away is not surprising.

 

Thank you very much for looking that up for me.

I did check the two wires on my IAT sensor connector and one of them was giving a 5v reading. I did not check my crank, cam, or app connectors yet for a 5v supply (ran out of time). What I am most interested in checking is my CAM connector because the diagram shows that it shares a 5v supply from the same pin as the oil and map sensors. If I am getting 5v at my CAM sensor, it would lead me to believe I may have a wiring issue going to my oil and map. If I don't have 5v at my CAM sensor, then I am leaning more and more towards a bad ECM especially based on the info you provided. If the ECM should be feeding 5v to the oil sensor but I am only reading .4v, then I suspect there is something wrong within the ECM.

 

Got the truck back up and running! Here's what happened. Hopefully this info can help someone else out.

Turns out the CAM sensor had failed and was shoring out the 5v supply. As a result, all other sensors that share the same 5v supply as the CAM sensor were acting up (that would be the OIL and MAP sensors). For some reason, that failed CAM sensor was also causing the WIF sensor to act up.

I found all this out by unplugging the CAM sensor and taking readings again from the MAP, oil, and WIF connectors and they all read the proper 5v. I installed a new CAM sensor and hooked everything back up and its all running perfect now.

Just my luck though, as soon as I got back from my test drive I noticed a trail of coolant. Upon inspection, I found a crack had developed on the plastic part of the radiator on the driver side. Once heated up and pressured, coolant was spewing out. One thing after another on this truck! I guess it's to be expected with a 300k mile truck.

Thanks for the help JRS