I have an '04 Dakota that has been powertrain swapped with a '99 RT

I've been experiencing issues where when the engine is running the gauges will go dead and the odometer will blink.

Also the truck seems a little weak and will shift up to high gears very fast. If you floor it will not drop to lower gears or rev out.

Having done the odometer trouble code test, I got a bunch of 900 codes that basically all said there was no communication to the PCM. (900, 920, 921, 940, 950, 999)

Using my scanner I found the following trouble codes:

P0123 - throttle position sensor A circuit high input
P0137 - 02 circuit low voltage bank 1 sensor 2
P0143 - 02 circuit low voltage bank 1 sensor 3

At this point I assumed I had a bad PCM and planned on retrieving the VIN stored on the PCM (since the VIN on the body has no correlation to the powertrain now) in order to order a new one.

Except when I plugged my scanner in, under vehicle information this is what I see:

Global Format
VIN#: N/A
Module#: $D1
CVN: 34 2F 8D 8F

What I need to know is this - can I order a PCM without knowing the VIN and it still operate correctly so long as it matches whatever PCM is installed currently? -

In short, what should my next move be?

I've read that a short in the sensor circuits can cause the PCM to behave similarly and the shorting issues will need to be resolved first before the PCM can be diagnosed.

I've also heard that you shouldn't change sensors *****-nilly until the underlying issue is resolved to confirm that they are reading accurately.

I am trying to take my time and use this experience to learn, so I really don't want to just start throwing parts at it.

So can anyone point me in the right direction as to what my next move should be??

Any info helps, thanks in advance!

 

Start unplugging sensors, and see if the PCM is more informative. One at a time please, and test after each one. The last one you unplug, that makes the PCM tell ya what you wanna know, is likely the problem.

 

thanks for the response,

What exactly do you mean when you say "that makes the PCM tell ya what you wanna know" ? As in, unplug sensors until a new DTC appears or?

what should I expect to see happen?

 

Hopefully, it will eventually hand you the vin, and other missing information........

Being an 04, several modules that also communicate with the PCM, and are concerned about VIN mismatch..... Are you getting ABS, or SRS lights/errors?

Essentially, what is happening is, the Cluster is losing communication with the PCM. (it gets all of its information on where to put the needles, and what lights should be on, from the PCM.) It might be as simply as a bad connection behind the cluster, a bad sensor somewhere, or a failing PCM..... Not having the VIN programmed usually annoys at least some of the systems on the truck, but, the cluster ain't one of 'em.

 

I went through and unplugged all the sensors I could get to one at a time.

Unplugging the O2 sensors got rid of my O2 sensor code.

But unplugging my throttle position sensor did not affect the throttle position sensor high intput code.

I have an airbag code because I have a quick disconnect steering wheel. I do not have an ABS light until the gauges die.

No matter what I unplug, or erase, the PCM doesn't display the vin. Is it possible there was no Vin programmed into it?

Right now the only way I can make my gauges work normally for a short period of time is to unplug the PCM and plug it back in. It works every time.

Is there a way to remove the PCM from the truck and get it scanned/tested?

Could the VIN from any Dakota RT be programmed into the computer?

 

I haven't seen anyone with a decent test bench for PCM's...... for the most part, all work is done with the PCM in the vehicle. VIN just needs to match what the other modules (ABS, SRS) think it should be. Which is likely the actual VIN of your truck.

I think you need a good scanner, that can show you live data. Need to have a look at what the PCM thinks is going on.

 

Yeah I'm almost thinking a DRB III would be helpful here.

I'm thinking my sensors are probably good because even though I have a code for the TPS, my live data shows the TP accurately. So obviously it is working.

The only thing left that that I haven't checked thoroughly is the wiring harness. But I was really hoping to not mess with going over every wire.

Is there info out there to tell me what readings I should get on the pins for the PCM connectors so I can test the sensor circuits for resistance ect.?

 

Maybe clear the codes, drive it for a while, and see what comes back.

If you can read live data with your scanner, and the data looks reasonable, that is sufficient for testing.....