2-Wheel ABS Malfuntion on '95 3500 V10 2WD Dually
Hello all before I get into the details of the problem, allow me to introduce myself:
My name is Shawn and I am an ASE Master Technician. I am currently employed as a Diagnositic/Drivability Technician and Smog Technician at one of the major shops in my area. I am a Toyota guy by history (I own four), but I am asked to work on just about everything in my line of work. I specialize in electrical diagnosis, and am completely stumped on this one.
1995 Dodge Ram 3500 2WD Dually V10/Auto with Rear Wheel ABS with 154k Miles that appears to be very well maintained.
The customer was driving the vehicle on the highway at normal highway speeds (More than 40 MPH) when they attempted to make a hard stop and the rear end of the vehicle came out from behind the vehicle and it wound up facing the opposite way on the highway. It was somewhat wet outside when this happened. According to the customer, the ABS and Brake lights were coming on intermittently.
Since the work order was put in my hands:
Test drove vehicle and was able to verify the customers complaint. Rear brakes would lock up 1/3 of the time under hard braking in wet road conditions over 40 MPH. ABS would function normally and pulse the pedal the other 2/3 of the time. Could not lock up brakes under 40 MPH - ABS would function normally. Could not recreate ABS light more than once. Pulled one code (Module can only store one code) code 11, which pertains to a stop light switch being on all the time, or a two footed driver (One foot on the gas, one on the brake while driving over 40 MPH.) Inspected rear brakes and found no abnormal reason why the brakes would lock up other than hydraulic force (I.E. no brake fluid or oil on the shoes or drums, no water in the drums). Shoes look they have been replaced within the last 10k miles. Differential speed sensor ohmed out at 1300 ohms dead cold, with the spec being 1000-2500 ohms. After doing extensive research on forums and other online resources, we decided to throw an inexpensive part - stop light switch - at it to see if the problem would go away. This did not correct the problem, and now I am looking for other possible causes.
During my research, I found a lot of threads describing this same problem, but I did not see any solutions other than the occasional stop light switch.
I have access to all wiring diagrams for this vehicle, and have not found any issues in any of the wiring yet. Since the problem is intermittent, it points more to a sensor or something mechanical (in my opinion), or worse yet, the Module.
Thank you for taking the time to read my detailed post.
Help me solve this problem, the flat rate is KILLING me.
Any input is greatly appreciated!