Help Needed With 1998 XJ SE Speedometer Problem

Please offer me some new ideas. I've read a lot of threads on several forums about similar problems with XJ's and TJ's and have looked extensively at hits from internet searches on the subject. So far, nothing that I have tried has resolved the problem.


Problem: Speedometer drops to a lower speed reading when vehicle accelerates. How far and how fast the speedometer drops seems to correlate to how hard I am accelerating. However, speedometer returns to correct reading under steady-state throttle or deceleration. Problem is consistent; not intermittent. A side issue is that when the speedometer drops, if the cruise control is engaged, it cancels the cruise control. The other gauges, lights, and indicators in the instrument cluster appear to work correctly.


Onset: Problem started in September 2011 while driving on pavement after about 1500 miles of mixed driving on or in pavement, gravel, dirt, dust, rock, and water during a week and a half of back country travel.



Actions taken:

• Instrument cluster actuator test completes successfully
• Three instrument clusters have been tried (two have full complement of gauges and one has idiot lights). The cluster with idiot lights is known to be good
• 05016261AA Cluster Connector Patch Harness has been installed per TSB 08-15-99
• Male pins on instrument clusters have been cleaned
• Another PCM for a 4.0L manual transmission XJ has been tried
• PCM connector C3, male pins C28 and C30 have been cleaned and female receptacles on plug have been shot with connector cleaner and then dried
• Grounds disassembled, cleaned and reassembled: Battery negative terminal, engine to firewall strap, G100 (right fender near battery), G101 (near alternator and next to G103) G102 (right rear on engine), G103 (near alternator and next to G101), G106 (near PCM), G108 (there are actually two of these ground studs under the dash near the headlight switch), and G200 (near airbag control module under the center console). Please note that the ground numbers in the 1998 Cherokee Service Manual are not consistent between the tables and the figures in the manual, so the ground numbers shown here are my best guess about the actual factory number.
• Airbag control module wire harness disconnected in accordance with Instruction Sheet K6855297 and left disconnected to eliminate this information source to the CCD bus
• Throttle position sensor disconnected to eliminate this information source to the CCD bus. This turned on the check engine light and caused the engine to die occasionally when returning to idle but didn't have any effect on the speedometer problem, so I reconnected the sensor
• Connectors C100 and C200 unbolted, disconnected, and blown free of dust. C100 male pins A11 and A12 filed and cleaned with connector cleaner and female receptacles shot with connector cleaner and blown dry

Vehicle Information: 1998 Jeep Cherokee XJ SE, 4.0L, AX15, power steering, Box4Rocks 231J doubler, 231DHD transfer case with Teraflex super short SYE, Dana 30 front with Elocker, Dana 44 rear with Elocker, rear disk brake conversion from ZJ, power mirrors, factory cruise control retro-fitted two years ago, full gauge set instrument cluster retro-fitted two years ago, rear window wiper/washer, air conditioning, and standard radio. Airbag control module was relocated from under drivers seat per recall. Trailer light connector added years ago. Driver seat belt switch disconnected. Does not have: Overhead console, ABS, power seats, power windows, security system, or tilt steering column.


Thanks in advance for your suggestions on what I should do next to trouble-shoot this problem.

Why haven't you done any trouble shooting at the Transfer Case extension/speedometer output housing, the Vehicle Speed Sensor (VSS) gear, and the wiring ? Any moisture or corrosion in the VSS wire plug will cause erratic speedometer behavior.

Yeah, I agree with Tim. I'd check the VSS.

Thanks for the suggestion. I will try this. The sensor was new with the SYE installation in July 2011 and I assumed (ass u me) a new sensor wouldn't be the source. However, the connector and wiring needs more than just the visual check I gave it. I will let you know . . .

Problelm solved! Thanks for directing me to look at the VSS. The transfer case yoke nut was not tightened to spec which allowed the speed sensor ring to slip on the output shaft. Tera Manufacturing issued TSB061505 which addresses this as part of mechanical and electrical issues to be considered with speedometer malfunction.

This was a good reminder for me to not get locked into exploring only the common problem/solution threads that come up when searching the forum.