ABS,Speed Sensor~Speedo? - Hemi Truck Club
 
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Old 04-14-2008, 08:08 AM   #1
 
Join Date: Jul 2004
Posts: 254
ABS,Speed Sensor~Speedo?

Friday I noticed my speedo jumping while in drive with my foot on the brake. Soon thereafter my ABS and Brake lights came on. I didn't get any codes when I hooked up the tuner and checked. The lights went off when I restarted the truck but came back on after sitting at a light.
I replaced the speed sensor on the rear diff and that seemed to work for a while. I am still noticing my speedo jumping although the ABS and Brake lights aren't on.
Are there any other sensors I need to check?

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Old 04-14-2008, 08:30 PM   #2
 
Join Date: Jun 2004
Posts: 742
ABS,Speed Sensor~Speedo?

² Vehicle Speed Message - Each time the cluster
receives a 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 vehicle speed message and reposition the gauge
pointer accordingly about every 88 milliseconds. The
gauge needle will continue to be positioned at the
actual vehicle speed position on the gauge scale until
the ignition switch is turned to the Off position.
² Communication Error - If the cluster fails to
receive a speedometer 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.
² Actuator Test - Each time the cluster is put
through the actuator 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 to determine the vehicle road speed. The PCM
then sends the proper vehicle speed messages to the
instrument cluster. For further diagnosis of the
speedometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING).
For proper diagnosis of the vehicle speed
sensor, the PCM, the PCI data bus, or the electronic
message inputs to the instrument cluster that control
the speedometer, a DRBIIIt scan tool is required.
Refer to the appropriate diagnostic information.

This is from the '03 manual.

JG
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Old 04-15-2008, 06:44 AM   #3
 
Join Date: Jul 2004
Posts: 254
ABS,Speed Sensor~Speedo?

Thanks for the info.
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