1998 PCM - replaced - still not fixed? - Dodge Cummins Diesel Forum
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post #1 of 3 (permalink) Old 04-11-2019, 10:41 PM Thread Starter
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1998 PCM - replaced - still not fixed?

My saga continues.
I bought a new PCM from these guys:
Suppose to be plug and play. I installed it and it didn't fix my issues.

What doesn't work:
- gauges do not move
- air heater grids do not activate
- alternator does not charge the battery
- odometer flashes same number
- (automatic transmission) Drive position = 3rd gear; positon 1 and 2 = 2nd gear (I think)
- fuel tank empty light comes on
-ABS and Park Brake light comes on

Gauge check/display 'C' codes:
920 - cluster not receiving vehicle speed from PCM
921 - cluster not receiving distance pulse from PCM
999 - error detected
So, basically, the PCM is not talking to the cluster

The grounds tested good.
CCD Bus has 2.46V

The dealership thinks I might have to sync the PCM to the truck, even though the unit is supposed to be plug and go. I think they just want to charge me to try it? Could they be right?

Has anybody had a similar experience?

What else could be wrong?

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post #2 of 3 (permalink) Old 04-11-2019, 11:48 PM
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IIRC, you'll need to set the gear angle ratio to get the PCM to report VSS/MPH
This will probably require the dealer scan tool to set it.
I use to do this with the DBRIII with replacement PCM's.

2016 Laramie 2500 CC 4X4 6.7L CUMMINS
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post #3 of 3 (permalink) Old 04-14-2019, 08:54 PM Thread Starter
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I figured it out! The Engine Speed Sensor (RPM sensor) must be shorting out internally.
I started trouble shooting by unplugging each of the 5V sensors related to the PCM and seeing if fixed the problem. When I unplug the RPM Sensor, all of the gauges work except the speedometer.
The transmission isnít working correctly but that seems to make sense as RPMís and the transmission talk through the PCM.
Thank you everyone for pointing me in the right direction.
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