289D Drive motor speed sensor faults 2685-8

flipz34 · 2026-06-17T19:15:01.000Z

I have a 289D, TAW05187, that has abnormal drive motor frequency faults for all 4 speed sensors (2685, 2686, 2687, 2688). It has the intermittent fault that only shows when moving the machine. I've gone through the service manual and all the wiring checks fine according to the troubleshooting guide. I initially started checking wiring at machine ecm and working toward the speed sensors themselves since it was all 4 sensors and I felt it was a common fault. 8V ref was reading about 7.95 at every point I tested it. All grounds I tested were good. I swapped in a spare speed sensor from a 279D that I had lying around with no changes to any readings. There is a small amount of hydraulic oil on the face of the sensor when I remove it. I know that could cause an incorrect reading on the sensor but the fault happens so quickly that I don't believe it's the source of my issues. I had a tilt cylinder fault 458-4 that went away when I replaced the sensor. I only dug into that because it used the same 8V reference. I've also got a 3700-3 inclinometer fault that has been around for quite awhile. We haven't looked into that one because the dealership said it won't affect anything other than the operation of the self leveling function of the machine and my 279D had had the same fault for about 6 years with no other side effects. Once I started looking into that I found that the inclinometer uses the same 8V ref. Could everything that uses that reference signal cause problems elsewhere in the circuit? I've googled "can an inclinometer fault 3700-3 cause 2685-8 speed sensor faults" twice and the AI said no the first time and yes the second so I'm reluctant to trust that. I have started looking into the 3700 and I think that I've got a ground issue on the inclinometer circuit as I get around 1000 ohms on step 2 of the 3700-3 troubleshooting tree. Most of the threads I find on this either don't resolve or come down to a sensor or wiring. Not came to that point as of yet. Just really looking for an idea on where to go from here. Should I track down the inclinometer problem in case it's the root of my issues or am I headed in the wrong direction. I have the service manual and diagrams for the machine as well as ET. Any advice would be appreciated. Thank you.

flipz34Junior MemberAug 30, 2026#21

So I finally got my issue corrected. We had Cat send a tech out and after doing most of what I had already done, decided that either the platform harness or the cab harness was bad. We had our 279D back to the shop so I swapped the speed sensor from it to the left drive motor of the broke machine. Left speed sensor faults cleared. Got a new sensor from Cat and put it in the right drive motor and right side faults cleared. Put the spare sensor back into the 279D (where it originally came from when I replaced the final drive) and it faulted in about 15 ft. I have no idea what the odds are of having 3 bad sensors doing the exact same thing are but I feel like I have a better chance of winning the lottery. Thanks again to everyone that offered help on this.

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