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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Dodge
Satisfied Customers: 1523
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Ram 2500 diesel: I have a 1999 dodge 2500 here that the speedo

Customer Question

I have a 1999 dodge 2500 here that the speedo bounces almost to 30 when driving, the brake and abs light come on after dynamic test at 15 mph. I have replaced the rear speed sensor twice and the transmission output speed sensor once, no change. I have checked wiring up from rear speed sensor and all is well. This is only a rear anti lock system. The trans will shift fine from first to second but the third and lockup hunt and are erratic, I checked line pressures they are within spec as are the governer and accumulator ports. Am I chasing a bad ABS module? This all occluded after replacing brakes rotors and calipers.
Submitted: 1 year ago.
Category: Dodge
Expert:  Juan Crespo replied 1 year ago.
Hi there. Welcome to our site. Since the rear ABS system gets its signal from the single sensor on the differential, I can't see how replacing calipers and rotors would have any adverse affect on it. Only thing I can see that's connected to all the issues is, as you already suspect, the EBC2 ABS module.The reason why I share your suspicion is that the PCM averages both speed signals (one from the ABS module, one from the sensor on the trans output shaft) before sending the final output signal to the speedometer. So, a bad speed signal from the EBC2 module may very well throw the PCM off, causing all the erratic behavior. Lacking access to a DRB-II scan tool to communicate with the system, I'd say your best bet would be to try another EBC2 ABS module. Kindly accept and rate my answer now if you think the information I've provided has helped you solve your issue. Otherwise, please reply. Best Regards.
Customer: replied 1 year ago.
Well I replaced the ABS module today with no change at all. I pulled the battery cables then unplugged each of the ECM connections, cleaned and put some dielectric grease on them. Still no change in speed or shifting. Any more ideas?
Expert:  Juan Crespo replied 1 year ago.
I do have some, problem is they all involve using a capable scan tool. Any chance you can borrow one of those?
Customer: replied 1 year ago.
I will be scanning it tomorrow with one that can get into the ABS system what all should I be looking for?
Expert:  Juan Crespo replied 1 year ago.
I'm not familiar with an ABS-only scanner, so I don't know if it can see the signal from the speed sensor in the tranny as well as the signal from the ABS sensor.
With a capable scanner, you could look at the speed signals coming from the two sensors; then compare the two and see whether the problem is in the PCM, the ABS module, the trans or the instrument cluster.
In any case, please let me know what you find tomorrow with the ABS scanner.
Best Regards.
Customer: replied 1 year ago.
Well the scanner was showing intermittent signal from rear speed sensor. I found the issue, the rear carrier bearings are wasted and let the tone ring drop away from sensor. With the 37" aggressive tires you couldn't hear a thing.
Expert:  Juan Crespo replied 1 year ago.
I wonder if we would've ever noticed that without the scan tool. Good catch! Best Regards.