I wanted to recap my journey through diagnosing and repairing the speed sensors and other codes on my 259D in case anyone else happens to have similar issues and looks up this post. Hopefully they can find it useful and this helps someone else the way old posts help me when i search them. I picked up a 259D recently, It runs fine no issues except the flashing caution light and the auto bucket level doesn't work. I had cat read the codes and this is what i came up with active round 1 7/10/2020: Machine control: 2685- 8 Left Drive Motor Speed Sensor #1 : Abnormal Frequency, Pulse Width, or Period 2686- 8 Left Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period 2687- 8 Right Drive Motor Speed Sensor #1 : Abnormal Frequency, Pulse Width, or Period 2688- 8 Right Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period 3700- 3 Loader Bucket Inclinometer Sensor : Voltage Above Normal Active in product Link: 1888- 3 Local GPS Antenna : Voltage Above Normal 4682- 3 Cellular Antenna : Voltage Above Normal Logged with very recent occurance: E879 (1) Hydraulic Tank Oil Filter Plugged 127 2557 3029 Lets start with the easy codes: E879 (1) Hydraulic Tank Oil Filter Plugged 127 2557 3029 (Replaced hydraulic filter, Code went away) 1888- 3 Local GPS Antenna : Voltage Above Normal 4682- 3 Cellular Antenna : Voltage Above Normal I noticed the GPS Antenna had broken wires right at the front "Brow" of the machine above the headlight, they are not a standard copper core wire so i dont have a way of making a repair... Installed a new antenna from cat Code still active, Hmm according to the cat tech these product links are under recall update from 3g to 5g, more on this later. 3700- 3 Loader Bucket Inclinometer Sensor : Voltage Above Normal Traced wires to the bucket sensor at the bucket and found 2 broken wires, repaired wires, tested for continuity from ecm through these wires, all good. Bucket auto level is working now... Now for the more involved repair: Machine control: 2685- 8 Left Drive Motor Speed Sensor #1 : Abnormal Frequency, Pulse Width, or Period 2686- 8 Left Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period 2687- 8 Right Drive Motor Speed Sensor #1 : Abnormal Frequency, Pulse Width, or Period 2688- 8 Right Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period Per the diagnostic procedure sent to me by a very helpful member on this forum i traced all the sensor and power wires to these sensors. Good power and ground at both right and left harnesses. Good continuity through both sensor signal wires from ecm to both right and left harnesses. No shorts between the 4 signal wires and ALL OTHER ecm wires. I did find 2 pins backed out of a plug on the left side but i dont know if they backed out while i was pulling the plug apart or were like that before... Removed sensors, cleaned and reinstalled. Caution light still flashing. At this point i hauled the machine back to Cat and had them plug back in. The only codes remaining at this point are as listed below: 2686- 8 Left Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period 2687- 8 Right Drive Motor Speed Sensor #1 : Abnormal Frequency, Pulse Width, or Period 2688- 8 Right Drive Motor Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period OK so i am down to 3 codes, tech recommenced replacing both sensors... 455$ for 2 sensors i ordered them up to stop this caution light flashing nonsense.... WRONG After installing the 2 new speed sensors as i was driving my machine off the blocks i noticed the caution light went from flashing slowly to flashing RAPIDLY. Shaking my head here now what have i done. Fresh day after some thinking: After researching why the caution light would go from flashing slowly to flashing rapidly my only thought was that i went from level 2 warning to Level 3, except i dont have a beeper screaming at me as a level 3 warning should set off. Come to think of it when i turn the key on initially i dont get a "Test" beep like these machines should... Without the ability to plug into the machine the only hunch i have is to see if my warning beeper is functional. Per the wiring diagram it should be somewhere close to the hand throttle and gauge cluster readout. After tearing down the right hand overhead console, sure enough the wire is cut leading to the warning beeper. I assume this was done by the previous owner to quiet down the obnoxious noise from all the codes? Reconnect the warning beeper wire, CAUTION LIGHT IS GONE. Disconnect the beeper, the caution light flashes RAPIDLY. No active codes at this time.
For anyone else troubleshooting the speed/direction sensors, it's worth noting that the ECM needs so see an output from them before it will clear an active code. In other words, once you've done your repair, you have to drive it backwards and forwards a bit to clear the code.
The OP and myself had been discussing this via PM before he brought it to the forum. His response - " [After replacing the speed sensors] as i was starting to move the machine i noticed the caution light went from flashing slowly to flashing rapidly... i ran the machine around up to full speed forward back etc. Caution light is now flashing rapidly." Chris, don't you think that if the circuit for the Action Alarm is interrupted (as in this case with a cut wire) it ought to generate a Diagnostic Code..? SIS shows nothing for Diagnostic Codes on the circuit for the Action Alarm, so why in this case would a cut wire to the Action Alarm (beeper) cause the Action Light to flash..? Everything that has gone on with this machine since the OP first contacted me over 2 weeks ago pointed to speed sensors, yet even after replacing them the Action Light would not stop flashing. Repair the cut wire to the Action Alarm and the Action Light stopped flashing.
Yes I do think an open circuit to the alarm should have generated a fault code, but to be honest the fact that it didn't doesn't surprise me nowadays. Recently I've come across several instances of faults that are not listed in SIS. Only a couple of weeks ago we had an excavator with an issue in the quick coupler circuit. After going through the problem in detail, both myself, a dealer sparky and Cat tech support agreed that the only next logical step was to replace the ECM. Guess what? No difference. Turns out that the coupler safety circuit will only detect coupler-closed if it also sees input from the AEC (auto idle) switch. This was totally undocumented in SIS and with the AEC switch being a simple two-wire open/closed affair, it didn't generate a fault or error code, and of course the nature of the problem didn't call for testing at any engine speed above idle. We only found it by chance after testing every single input and output, logically, in order through ET.
I realize this is old but fighting right drive sensor #1 I just changed it but I have code wrong cellular antenna also code gps antenna voltage low and code cellular antenna voltage low. Anyway any of these came up because I have backup beeper unplugged it's been unplugged for over a year and now machine has 629 hours on it and sensors are going bad like really?? But thanks for the little bit at end were someone said you gotta drive it a bit to get alarm off I turned on machine looked at info page still showed 16000 rpm from right drive speed sensor machine off key on was about to snap of I gotta buy et just to clear codes cause I'm not paying cat to come click his laptop mouse couple times I can do that part myself to hate new machine sensors but love running nice equipment good day all
Can you give some basic info please. Machine Serial Number.? How are you reading Codes, the RH display or some other way.? What diagnostics did you make before replacing the speed sensor.? Do you still have an Active Code for the #1 RH Spd sensor.? If so, what Code do you have.?
I have a 2014 289D sn TAW00986. 1100 hrs Just recently replaced the right joystick position sensor. I am getting active codes 2688-8 and 2687-8. Both reference the right hand drive motor speed sensors 2 and 1. Service screen shows right Drive motor stuck around 16000 rpm. Noticed this thread and was wondering if there was a resolution for these codes. I had to mess with the wiring harness under the right and left hand armrests when repairing the right joystick position sensor and thought this could be a short in a ground wire or something? Or could the sensors both go bad at the same time? Any help is appreciated. This was an intermittent problem at first and has become steady with the beeper going off any time the machine is operating. Thanks
Yes there is. See the attached troubleshooting procedures. What you may not realize is that there is a single sensor body with two sensors inside it, each fed by a common power and having a common ground. Only the sensor signal wires are separate. Each sensor (LH & RH) is connected to the machine harness via a 4-pin connector. The fact you have Codes for both #1 & #2 sensors on the same side at the same time likely points to an issue with either the power or ground to that side. I would suggest to swap the sensors side to side and see if the problem moves with it. (Part of the procedure is to remove the sensor and check the nose end for contamination, so you have to remove one sensor anyway.) If the problem stays on the RH side then you have a wiring fault in the RH machine harness or connectors.
Are the sensors located on the drive motor itself? Where exactly would their location be? Thanks so much
Back side of the drive motors, facing the machine chassis. Check the pdf docs I attached above and look on the RH side for a 4-pin connector with those wire colours on it. The LH one will be in the same place relatively speaking.
Here's an illustration of the LH side sensor orientation. The sensor is only held in place by one Allen screw #3 but even when you remove that screw it is likely to be tight in the housing because of O-Ring #4 in the 2nd illustration.
Thank you! I cleaned the machine up today and the wires look stretched from all the mud that was packed in there. Im guessing it is a short. Will check back in once i get in there. Thanks again for the assistance
Finally found time to work on this. I swapped the sensors and the problem stayed on the right. Right drive motor sensor still showing 16,700 rpm. So the issue must be with the wiring from the ecm? Does anyone know if the wiring passes near the right joystick in the cab as after I replaced the right joystick sensor and moved around the wiring harness near it, this right hand drive motor sensor code began. Not sure if i could have caused a short near the right joystick?
I'm not sure for your 259D, but I just went through this extremely frustrating troubleshooting process with my 299C. The wiring for mine follows the hydraulic hoses from the track drive to under the cab and up behind the cab seat where the ECM sits. Not sure if that's in the same area you worked on before. The one thing I learned was that even though resistance and short testing come up good, doesn't mean there is no problem in the harness. I had one that wore all the way through sheathing to copper and all the wires tested perfectly. One of them must have been shorting out to the chassis. It was not visible until I pulled it out all the way out. One other lesson learned is not to trust the new sensors. I put in a new one that did not work.
Thank you for the information. My 289d is probably wired the same under the cab so i will check that out next. I’m glad i didn’t just buy a new sensor.