skyysipper

98 XJ Automatic. Starts and runs well.

Key in turned to on position - 'no bus' and no gauges(any). Disconnecting the TCM brings the cluster back to life and odometer appears. Plug TCM back in and start xj and drive for a while and then cluster dies again...

I have swapped out the TCM and PCM and Instrument Cluster with known working modules and exactly the same every time. Disconnecting the TCM brings the cluster back to life. Sometimes flicking the wipers makes it come back to life as well.

Strange thing is the same thing happens if I turn the ignition to the on position, and then disconnect the PCM C3 connector, all the gauges come back to life - just presented with no bus, and plugging it back in makes the no bus disappear...

I have found and cleaned to bare metal every ground except G108, which I cannot find under the dash... but the pin on the cluster C2 harness tests good for that ground. (How do I get to g108??)

I have cleaned/scraped the contacts behind the cluster. Removed all the connectors held in by 10mm bolts, cleaned the contacts and tightened up. Cleaned the contacts in the 3 wire connectors near rear of engine compartment passenger side. Checked every fuse.

Is there any reason in particular that disconnecting the tcm or the pcm c3 connector and plugging it back in would bring the cluster and bus back to life????

skyysipper

(Key in/ON position) Disconnected all the sensors one at a time and all together... No change..

Voltage on harness to sensors tests 5.2 volts.

With all sensors disconnected (or connected), Voltmeter set to 20V, simply touching one pin on the CDL (pin 11, ccd bus) with one probe from the voltmeter woke up the gauges and bus. Other probe wasn't touching anything....

Seems like the bus isn't getting a wake up signal...? Totally stumped

CCKen

Do a quick health check of the CCD Bus and the termination resistors in the instrument cluster and the PCM.

See schematic below.

Connect everything but the battery. Remove the connector from the battery negative post.

Turn ignition switch to OFF/LOCK.

Set your digital Ohmmeter to 200 Ohm scale.

At the DLC, touch pin cav 3 (+) and pin cav 11 (-). You should see 60 Ohms if both termination resistors are on the bus. If you see 120 Ohms, one has dropped out.

Reconnect the battery.

Turn ignition switch to ON (engine not running).

Set the voltmeter to 20 VDC (to start with).

Touch DLC pin cav 3 (+) and pin cav 4 and/or 5 (-). You should see around 2.5 volts. Switch to the 2 VDC scale if you see a very low voltge.

Touch pin cav 11 (+) and pin cav 4 and/or 5 (-). Again, you should see around 2.5 volts.

See limitations on the schematic.

End of tests - for now.

Report back your findings.

Cheers

skyysipper

Thanks for responding CCKen,

Battery Disconnected/No key:
Battery Connected/Key on: Touching pins 3 or 4 with the voltmeter doesn't always work for bringing the gauges and bus back to life, but disconnecting any of the modules does...

CCKen

Why would you think that touching 3 to 4 would bring the bus back? Generally, if you disconnect a module from the bus and it comes back to life it means the bus has been corrupted by that module and the voltage readings would show it, but you don't see bad voltages.

I take it that all the modules are connected when you got those DLC voltage readings.

Those are almost textbook readings. The 63 Ohms is a little odd though. Generally it's dead nuts at 60 Ohms. Might be your meter tolerance. Using the 200 Ohm scale, hold both leads together. Write down any reading you get and subtact that from any reading you get when reading a circuit.

With odd goings on like you're seeing I would strongly suggest you address two critial ground points in your engine bay. When I say address, I mean disassemble the ground connections and scrub the wire terminal ends with Scotch Brite pads, remove any rust from the chassis/engine face connection, then reassemble securely.

The main one is the gound point at the ignition coil mount studs (G101). It's the engine ground for the battery AND the ground for the TCM and PCM. Make sure these connections are free from corrosion and secure.

THe other critical ground point is the ground point for the short negative cable from the battery negative post to the right inner fender (G100). This is the main battery to chassis ground. It MUST be free from corrosion.

If you need some pics I'll post a link to them.

skyysipper

I've no idea why touching a single pin 3 or 11 on the DLC with the voltmeter on set to 20V would bring back the gauges and bus, but more often than not it does. Even just touching it for a second.

I've done all the grounds... even managed to do g108 today. Have done g107 right side of dash. In the engine bay the two grounds at the ignition coil, the one near the dipstick, the one on the firewall, and the one at the negative battery terminal. (wire brushed the heck out of everything)

Unplugging any module (TCM, ACM, or PCM) always seems to bring it back to life, then plugging back in and it stays for a while. Swapped out known good TCM/PCM/Cluster and exactly the same results.

CCKen

Do you have a 98 FSM?

When touching the DLC pin cavs 3 or 11 with the voltmeter probe do you have the key to ON, or do you have the engine running at the time?

skyysipper

Am testing with the key in ON position, engine not running. I have access to ALLDATA.

CCKen

This is an odd one.

Touching a pin cav on the DLC with a voltmeter probe makes the instruments come to life - It's almost lke you are adding another module to the CCD Bus and the PCM is trying to communicate with it.

Go to section/page 8W-30-23 of the FSM and you'll find the CCD Bus diagram. Notice the Diagnostic Splice Block. I guess you have one. It was eliminated starting in '99.

The Splice Block is located near the DLC (Gray connector). Maybe something's dicked up in the Splice Block. Check security of the connection. Try wiggling the harness going from the DLC to the Splice block (Key ON) and see what happens.

Also, pull the DLC down and check the wiring at the DLC for corrosion and/or loose wires.

skyysipper

Wiring looks okay at the diagnostic splice block..

Key on position/engine still off: Unplugging and plugging back in the diagnostic splice block brings the bus and gauges back to life... same as removing a module and plugging it back in...

DLC wiring looks okay

Wiggling around the bundles of wires doesn't seem to do anything

CCKen

What do you mean by unplugging and plugging back in the DLC? Unplugging and plugging back in what?

Here's an important tip: DO NOT unplug any sensor or module (especially a PCM connector) with power on the PDC bus, battery or alternator. It may, or will, damage the PCM.

skyysipper

Not the DLC, the diagnostic splice block... unplugging it and plugging it back in brings the bus and gauges in. it is plugged with just a connector the links the five violet wires together and the five white wires together.

All the unplugging and plugging of the modules brings the bus back only when key is in on position.. doesn't make a difference if the key isn't in or in off position.

Would the fact that flicking the wiper spray back and forth sometimes brings the gauges back have any meaning?

skyysipper

So after days of cleaning and renewing grounds and repeating such. Replacing cluster harness, Trying known working PCM, CPS, ACM, TCM, etc.. Disconnecting all sensors one at a time. Numerous resistance and voltage checks..

Problem is solved. It was a very intermittent issue and some of the tests seemed to have varying results which made it very hard to track down, but eventually found by probing the CCD bus wires at the Diagnostic Splice Connector found the WHT/BLK wire that runs from the DLC to the cluster had a fluctuating resistance when it should be less that 1 ohm. Found the problem location and spliced in a new wire twisting according to specs and now works fine!

Thanks for all the help!

CCKen

Cool.

Thanks for the follow up.