Hey guys. I'll try to make this short.

Car: 2000 XJ Classic, 4.0, 4x4

Background: Replaced TPS last year. About 6 weeks ago, had similar symptoms (RPM jumping 500-1k and not wanting to stay in 4th). Check engine light came on this time and showed 3 or 4 codes, one of which being a circuit high on the TPS. Tested, replaced, code went away. Other codes were o2 sensors, they magically took care of themselves. The last code was Ordered and replaced all 3 solenoids in the transmission this past weekend. Filled with a few quarts, cleared the fault, and test drove. Problem was solved as the car shifts through all gears perfectly fine and maintains ~1500rpm in 4th cruising at 50mph. The next day the check engine light came back on, same fault code. Car still drives just fine, but the fault code is there.

Today:
- Unhooked negative side of the battery for ~30 minutes to ensure the ECU/PCM whatever was cleared of the code. Still there when I turned the car back on. I do have one of those $30 amazon OBD2 scanners and I clear the fault with it, but when I turn the car off and back on the CEL turns back on.
- Checked fuse 11 in the passenger fuse panel and it is fine
- Checked the brake button (?) above the brake pedal to make sure it wasn't interfering and causing the clutch on the torque converter to not engage. It seems fine.
- Checked wiring at the harness connectors in the enging and there are no bare wires that I can find. I'm unsure of how to check for shorts in this wiring, however.

Question: Cruising at 50 and constant throttle, if I tap my brake, my rpms jump about 2-300 for a brief second. Is this how this clutch solenoid is supposed to function, or is this the opposite? None of the forum posts that I have found make it clear which is the correct way.

Is there a surefire way for me to test the wiring to ensure there's not a short in the few wires that would connect the solenoids to the rest of the wiring harness? Please be specific..testing wiring is not my specialty.

Is there anything else for this code that I might be missing and could test? I have no stutters, no stalling, maintains constant rpm when at a stop and seems to react at the push of the throttle. The only thing I might notice is a very slight lack of power on take off, but this might be my mind playing tricks because of the CEL. Also, sometimes when I start the car she has a little hitch-in-her-step where I might have to hold the starter down a second longer than normal. Not sure why.

Thanks

 

"Question: Cruising at 50 and constant throttle, if I tap my brake, my rpms jump about 2-300 for a brief second. Is this how this clutch solenoid is supposed to function, or is this the opposite? None of the forum posts that I have found make it clear which is the correct way.

This is normal.

Is there a surefire way for me to test the wiring to ensure there's not a short in the few wires that would connect the solenoids to the rest of the wiring harness? Please be specific..testing wiring is not my specialty."

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I suspect your transmission Input Speed Sensor may be at fault.

Here's some test pertaining to the ISS:

INPUT SPEED SENSOR (ISS)

The TCM uses the Input Speed Sensor (ISS) to detect transmission solenoid functional faults (P0751 solenoid A functional fault, P0756 solenoid B functional fault, P0740 TCC solenoid C functional fault). The ISS is a variable reluctance sensor. Changes in the reluctance of a magnetic circuit caused by the passing of the rotor lobes on the overdrive clutch drum result in the ISS outputting an AC periodic voltage wave form. The frequency and voltage of the wave form are proportional to the transmission input speed.

NOTE: SINCE THE OD/CLUTCH DRUM IS STATIONARY IN 4TH GEAR OR WHEN THE VEHICLE IS IN GEAR, BUT NOT MOVING. THERE WILL BE NO ISS SENSOR SIGNAL

P0743 was changed to P0740 in 2001. P0743 is not addressed in the 2001 diagnostics manual.

'99 code:

P0743 (M) Torque Converter Clutch Solenoid/ Trans Relay Circuits

An open or shorted condition detected in the torque converter clutch (part throttle unlock) solenoid control circuit. Shift solenoid C electrical fault - Aisin transmission

2001 code:

P0740-SOLENOID C FUNCTIONAL FAULT

When Monitored: Continuously with Solenoid C (TCC) energized.

Set Condition: When the solenoid is energized and the Engine RPM does not equal the Transmission’s Input Speed RPM or when the solenoid is deenergized and the Engine RPM equals Transmission input RPM.

POSSIBLE CAUSES

TPS DTC P0122 PRESENT IN THE TCM (TPS Fault)
TPS DTC’S PRESENT IN THE PCM
TCM DTC’S P1748 AND/OR P1749 PRESENT (TPS Fault)
INTERMITTENT WIRING AND/OR CONNECTORS
TRANSMISSION OIL BURNT AND/OR CONTAINS EXCESSIVE DEBRIS
INTERNAL TRANSMISSION

Testing:

You'll need a manual ranging digital volt/ohmmeter and two safety pins (back probes).

Review the TCM pinout and test procedures completely before beginning.

Access the TCM by removing the plastic trim panel and steel knee blocker from below the steering column. The pic below shows your TCM.

Remove the battery NEG post connector before removing the TCM connector.


.
Do all of these tests and report back each reading. You never know what you'll find.

TCM Pinouts:


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Tests:


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I read your reply during my lunch break yesterday, and ironically enough when I left work the Check engine light never came on. This morning, still no light. That's the joy of electronics right? Car has just a little slip getting into reverse, but I'm probably running a little low on fluid.

Can't thank you enough for that reply. I have some time tonight that I'm going to dedicate to testing the things mentioned and I'll report back.

 

I know this is an older thread, but I followed all the diagnostic steps and all show good. Have changed solenoids and TPS, topped off fluid, checked brake switch and still get a TCC code on my 2000 XJ. Seems to drive fine. Any thoughts? TCU bad?