Electronic speedometer problems

[kyleag89]

Ok so in my 93 XJ the speedometer and odometer are not working. I replaced the VSS and is still doesn't work. Anyone have any ideas on what else to check? I also swapped out the entire gauge cluster from my 94XJ and it does the same thing.

[Eagle]

There's a fuse -- did you check that?

[kyleag89]

Are you talking about the fuse under the dash for the Inst. cluster, interior lights, etc? Is there another fuse I don't know about? Every fuse under the dash is good, I checked them with a test light.

[HOrnbrod]

Your tach signal is generated by the ECU. The output is pin 43, a GRAY/ LT BLU wire. Unplug the connector from the ECU and make sure this pin is not recessed into the connector. If okay, check for continuity from the ECU pin 43 to the cluster connector.

[kyleag89]

Is the ECU the black box located on the drivers fender near the headlight? If it is I have a spare I can try swapping in.

[HOrnbrod]

Is the ECU the black box located on the drivers fender near the headlight? If it is I have a spare I can try swapping in.

 

Yes. Do you have a meter and do you know how to use it? It's much easier than just guessing and swapping parts.

[kyleag89]

Yes I have a nice meter and can use it, but I figured it would be easier than trying to test the little pins. When you say check for continuity between pin 43 and the cluster, you mean the blue/grey wire to the gauge itself? Looking for a break in the wire right?

[HOrnbrod]

Continuity = Zero (or very close) ohms between point A and point B. No breaks or shorts to ground. Since you have a spare ECU, eyeball the connector pins first. If all okay, swap it in. If still no tach indication, do the continuity check. Be advised that swapping in another unverified ECU might cause other problems.

[kyleag89]

Thanks hornbrod I will swap it tomorrow and let you know what happens.

[kyleag89]

Ok so I did what you said and checked the harness and checked the wire for continuity. They both checked out ok and the speedo worked for 27 miles this morning then stopped. Should I try swapping the ECU and see what happens?

[maddzz1]

Sounds like a loose connection somewhere since it worked for a short time after you messed with the wires.

[kyleag89]

I was just outside now, I took the dash out and tested the gauge itself and the circuit paper. Everything checked out good so I may just run a new wire from the ECU to the gauge cluster.

[HOrnbrod]

Ok so I did what you said and checked the harness and checked the wire for continuity. They both checked out ok and the speedo worked for 27 miles this morning then stopped. Should I try swapping the ECU and see what happens?

So the speedo stopped working after the ECU warmed up? If your spare ECU has the same p/n as the original, I'd stick it in and give it a shot.

 

Everything checked out good so I may just run a new wire from the ECU to the gauge cluster.

You said originally you had continuity from the ECU to the cluster connector. So why do you want to run a new wire??

[kyleag89]

Sorry I am confusing myself. The 92 ECU will not work in my 93 so thats out. I guess I can grab one from the JY but they charge $50 and its a gamble. I am going run a new signal wire from the VSS to the ecu because I think that wire is intermittent. Someone has probed the connection at the trans connector against the firewall, so I think there may be an intermittent problem with that wire somewhere.

[kyleag89]

I swapped the 92 ECU in and it has been in and working for the whole day.