Hello all,

I'm working on getting my new-to-me Ram 2500 with the 5.9 magnum running right and I have a few questions.

there are 3 codes that I am dealing with right now:

P0505 - IACV idle air control motor circuits
P1281 - Thermostat Inactive
P0308 - Cylinder 8 Misfire Detected

before I started messing with things the truck generally ran fine (CEL was on). I noticed that the truck was starting to pop/backfire under harder acceleration (sounds like its backfiring through the intake), that's what prompted me to start digging into things..

Currently I'm working on fixing the IACV issue. The old IACV was definitely shot - but stuck in a position that resulted in a normal idle. I put a new IACV in the truck and now the truck idles at like 1500 RPM, and I spent all day today trying to figure out why that is.

What I found is:

1. The truck is idling high because the IACV is wide open.. the PCM cant seem to actuate the IACV - the probe(?) does not move and is staying in the open position. There are no vacuum leaks that I am aware of. I also tried swapping in another new IACV with the same results.
2. Two of the wires on the 4-pin IACV plug oscillate between approximately 0 and 5v when the key is in the on position. Is this supposed to be at 12v or is this supposed to operate at 5v like many of the other PCM sensors/functions?
3. There is continuity between all 4 pins on the IACV plug and the corresponding PCM plug (plug A (black one) pin #'s 10,11,19,20) and there is no continuity between these wires and the pos or neg battery terminal - I think that this tells me that the wires are in working condition and not shorted.
4. The engine coolant temperature sensor appears to be working and delivering the correct resistance to the PCM. measuring the resistance of the sensor itself at room temperature yields approx. 8kohm. plugging the sensor into the wiring harness and measuring the resistance between the corresponding PCM plug pins (plug A (black one) pin #'s 4 & 16) yields the same resistance.
5. One thing I discovered when testing continuity on the various wires - the Black and Light Blue "Sensor Ground" wire, Circuit K4, (PCM plug A Pin #4) has continuity to the battery pos terminal. given that this is a ground wire, this is concerning. However, this ground wire/circuit (K4) is used for many sensors - all which seem to be functioning normally. Can anyone confirm that this is normal?

Based on the diag results I think it is a PCM failure, and I have ordered a new one, however, the K4 circuit continuity to pos battery terminal is concerning.

Any advise or input is greatly appreciated.

 

What year is your truck? Did you clean out the throttle body before putting on the iac? What brand?

 

A little late getting back to this thread (took forever to get the part) but I have an update:

I put a new ECM in the truck and it idles perfectly fine now.. However, I am now getting a P1764 Governor Pressure Sensor Low code. The truck clunks out if I put it in drive.. Reverse, 1 and 2 work if I select them manually, however the truck feels like it does not have full power, and will stall if breaking hard.

I'm guessing this has something to do with the Governor Pressure Sensor talking to the ECU. I hope there is some way to fix this with a software update.

 

And this is a 2001

 

Did you have that code with the original PCM?

 

No, only the codes described in my first post (which are gone with the new PCM). Never had any transmission problems prior to the new PCM install.

I did some digging in the FSM to try to understand the interaction between the governor sensor, transmission control solenoid, and the PCM and I'm going to try to check voltages later today. sent an email to the PCM referb company to see what they can do.

 

They will try and convince you your trans is shot. Prolly try and sell you one too. If they recommend another PCM, I will be stunned.

 

Do you still have your old PCM or did you send it to the rebuilder for an exchange? If you still have the original PCM, you could plug it in to double check..

 

You seem capable and willing to try. I would suggest you find a copy of the 'PowerTrain Diagnostic' manual for a 2001. It covers each trouble code with a diagnostic tree and has a lot of in depth information the FSM was never designed to deliver. Anything with a wire attached is addressed pretty much. A lot of the diagnostic work is centered around the DRB scanner, but with wiring diagrams and a voltmeter you can handle much of the work.

 

So with the old ECM (original Dodge) no transmission issues or trans related codes. But the old IACV issues/codes come back (obviously).

I am sending both the rebuilt unit and my original Dodge back to the ECM refurbishing company to see if they can make something happen! At least they seem willing to make it right.

​​​​​