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Chris
Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 13876
Experience:  Dodge/Cummins and Chrysler Certified Master Tech
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My 2007 Dodge Ram 1500 5.7 4x4 speedo stopped working. I

Customer Question

My 2007 Dodge Ram 1500 5.7 4x4 speedo stopped working. I replaced the rear speed sensor in the pumpkin of the rear end did not fix what else could be wring
Submitted: 2 months ago.
Category: Dodge
Expert:  Chris replied 2 months ago.
Hello and welcome to just answer.
Customer: replied 2 months ago.
Hello so what should I replace next on my 07 dodge
Expert:  Chris replied 2 months ago.
The speedometer gets the speed signal from the ABS module. It is possible that there is a problem with the module or it may be a wiring issue. Go to your auto parts store and ask them to check out the diagnostic trouble codes in the ABS module. Then tell me what they find. Most auto parts stores will do this for free.Chris
Customer: replied 2 months ago.
Is it possible that the input/output sensor in the transmission is bad?
Expert:  Chris replied 2 months ago.
Well it is possible, but your truck uses the Wheel speed sensor signal from the ABS module for the speedometer. So we need to check and see if the ABS module is seeing a valid wheel speed and sending it to the instrument cluster.ChrisChris
Customer: replied 2 months ago.
Local parts store hooked up to and it read abs read fine I checked voltage and compared it to another dodge like mine all that checked out
Expert:  Chris replied 2 months ago.
Is the check engine light on while driving?
Customer: replied 2 months ago.
just came on
Customer: replied 2 months ago.
Code read abs sensor
Expert:  Chris replied 2 months ago.
Aha! Send me your VIN number. I want to check out the options list.
Chris
Customer: replied 2 months ago.
1d7hu18227s252792
Customer: replied 2 months ago.
I also just replaced the speed sensor on the front of the transmission
Expert:  Chris replied 2 months ago.
Ok, if you still have a speed sensor code, then there may be a problem with the wiring or connector back at the sensor on the rear differential. Do you have an ohm meter and know how to use it for checking circuit continuity in a wire?
Customer: replied 2 months ago.
I have a meter
Expert:  Chris replied 2 months ago.
Ok, I will send you the ABS module connector pinout on my lunch break today. Then you can check the 2 circuits between the module connector and the speed sensor connector. I will get that to you asap.
Chris
Expert:  Chris replied 2 months ago.

Ok, click on the link below to see the connector. Also check that left front wheel speed sensor. That sensor may be bad.

Chris

Customer: replied 2 months ago.
I had it hooked up at a shop they told me they are getting no voltage out of the output sensor on the transmission and if the sensor didn't fix it that I would need a pcm is that correct
Expert:  Chris replied 2 months ago.
Hmmmm, I don't think so, but let me check.
Expert:  Chris replied 2 months ago.

No it is not true. The speed signal comes from the ABS wheel speed signal/

Read this and show it to the guys at the shop:

\

OPERATION

The speedometer gives an indication to the vehicle operator of the vehicle road speed. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Controller Area Network (CAN) data bus.

The speedometer is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

  1. Vehicle Speed Message - Each time the cluster receives an electronic vehicle speed message from the PCM it will calculate the correct vehicle speed reading and position the gauge needle at that relative speed position on the gauge scale. The cluster will receive a new message and reposition the gauge pointer accordingly about every 88 milliseconds. The gauge needle will continually be positioned at the relative vehicle speed position on the gauge scale until the vehicle stops moving, or until the ignition switch is turned to the OFF position, whichever occurs first.
  2. Communication Error - If the cluster fails to receive a speed message, it will hold the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the OFF position, whichever occurs first. After three seconds, the gauge needle will return to the left end of the gauge scale.
  3. Self Test - Each time the cluster is put through the self test, the speedometer needle will be swept to several calibration points on the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the Vehicle Speed Sensor (VSS) or electronic wheel speed messages from the Controller Anti-lock Brake (CAB) to determine the vehicle road speed. The PCM then sends the proper vehicle speed messages to the instrument cluster, also known as the Cab Compartment Node (CCN). For further diagnosis of the speedometer or the instrument cluster circuitry that controls the gauge, (Refer to 08 - Electrical/8J - Instrument Cluster - Diagnosis and Testing) .

For proper diagnosis of the VSS, the CAB, the PCM, the CCN, the CAN data bus or the electronic communication related to speedometer operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.

Customer: replied 2 months ago.
If I'm understanding that correct the speedo is ran off of the wheel speed sensor in the driver side wheel bearing I can't see it being the PCM since the speedo worked then two hours later didnt
Expert:  Chris replied 2 months ago.
Exactly. If you have a wheel speed sensor code in the ABS module, then I recommend fixing that first. Once that is fixed, your speedometer will most likely start working again.Chris
Expert:  Chris replied 2 months ago.
I hope that this information is helpful and if so, would you kindly take a moment and rate my service using the just answer star rating system? I would really appreciate it. I will still be able to help you out even after you rate me.Thank you!Chris
Customer: replied 2 months ago.
Last question every fuse bank in my fuse box should have 12 volts right I have 1 spare that has 0 volts and 3 that have 9 volt
Expert:  Chris replied 2 months ago.

Well some fuses will only have power when that circuit is powered up. So it is normal for not all fuses to have 12 volts all the time. It depends on the circuit.

Chris

Customer: replied 2 months ago.
I checked the wires on the ABS module CAN C BUS +
CAN C BUS - are shorted together should they be?
Expert:  Chris replied 2 months ago.

No they should not be shorted together actually. Do you have CAN bus codes in the system?

Chris

Customer: replied 2 months ago.
Idk how do you get those
Expert:  Chris replied 2 months ago.

Using a code reader that can communicate with the ABS module. If there are no CAN bus codes, then don't worry about it.

Chris

Customer: replied 2 months ago.
Then no the computer didn't bring up any codes for the abs module
Expert:  Chris replied 2 months ago.
Ok, then concentrate on thst vehicle wheel speed sensor. Once that is working, you will get your speedometer working. The guys at the shop should be able to connect their scan tool and check that signal while driving the truck. If the sensor on that left front wheel is bad, then have it replaced.Chris
Expert:  Chris replied 2 months ago.

Hello, just checking in to see how it is going with the truck.

Chris

Customer: replied 2 months ago.
Wheel sensor did not fix it
Expert:  Chris replied 2 months ago.

Is the ABS module actually on line and working? Has a capable scan tool been connected to it and see if it communicates and displays a wheel speed signal?

Chris

Customer: replied 2 months ago.
I had it scanned again and got a code for a can c bus short
Expert:  Chris replied 2 months ago.

That may be causing a communication issue between the ABS module and the PCM and speedometer. Get that CAN C bus circuit fixed before doing anything else.

Chris

Customer: replied 2 months ago.
Where is that circuit at
Expert:  Chris replied 2 months ago.

It is a 2 wire circuit that runs between the PCM and the ABS module and the instrument cluster, air bag module, & TIPM, (underhood fuse box). Let me see if I can find a diagram of the CAN C bus.

Chris

Expert:  Chris replied 2 months ago.

Click on the link below to see the CAN C bus circuit diagrams. Print it out and send it to your mechanic.

Chris