Hello, I'm working on a Cat 259D ser#CW901026. It has codes 2685-8 and 2686-8. The customer replaced the speed sensor with a new one from Cat and from what I can see, the harness looks good. However, when I start it, release the parking brake, and start moving the joystick, the left track starts moving in reverse and there is no way to control it. I need to turn the skid steer off to get it to stop. I'm wondering if it is a speed sensor problem or if there is a problem with the left side drive pump or controller that's stuck or something rather than a speed sensor. I tried unplugging all 4 drive control solenoids on top of the pumps and after moving the joystick some, the left side started moving in reverse even with all the solenoids unplugged. So i'm thinking it's a pump or servo control but maybe I'm on the wrong track and need to check the speed sensor some more? Thanks
As a first step I would suggest a recalibration of the proportional solenoid valves (four in total) for the LH & RH hystat pumps. That may confirm the presence of a mechanical fault inside the LH pump but you need to attempt to do the recal first. The calibration will require Cat ET. Attached the troubleshooting procedure for the 2685/2686 speed sensor Codes. The presence of both Codes on one side would suggest a problem in either the common power or common ground connections to the speed sensor - which is actually two sensors in a common body. EDIT: Come to think of it, troubleshoot the speed sensor Codes FIRST. It may be the pump is being commanded to do strange things on the back of a pair of erroneous sensor signals.
Thanks a lot! I'm an hour away from the machine and haven't got back there yet, but I'm planning to go this morning. I'll let you know what I find...
Just a thought. Pull the sensor first and clean the nose end of it. They are magnetic and if any stray particles of metal have been flying around in the drive motor that could seriously screw up the signals from both the #1 and #2 sensors.
Ok, just an update on this machine. I had a tire blow last Friday and didn't get to the job until this week. I unplugged the wiring harness from the sensor and tested voltage, resistance, etc. following the troubleshooting procedure. Everything tested fine so then I pulled the sensor out (which the customer had already replaced) and I did not see any metal or damage to the sensor. Then I put it all back together and went to do a forward and reverse pump calibration with Cat ET. I tried the forward calibration first but it failed and said something about left side reverse movement detected. Then I ran the reverse calibration and it ran through it but gave a warning 10D4- Left Pump minimum current out of range low. I tried the forward calibration again and this time it completed successfully. Then I tried reverse and it also finished successfully. The codes disappeared and the machine drives great now. So I'm not quite sure what to think. Do the pumps need to be recalibrated every time a speed sensor goes bad? Or did the pumps get out of calibration and the speed sensor never was bad? Not quite sure what to think, but at least it's working now!
Generally replacing a sensor should not require a pump control solenoid recalibration but I guess it can happen. Was the replacement sensor that the customer installed a genuine OEM or a "will fit".? sometimes you have to run calibrations multiple times before they "take". It's kind of the nature of the beast. I would suggest that you keep an eye it going forward, although now it has accepted a calibration I reckon it will probably be OK.
The customer said he bought the sensor from Cat so I assume that he actually did. Have no reason to think otherwise but you never know with some people