P1898 P0700 tranny DTC code Fix - SOLVED!

I kept getting 2 transmission codes and a check engine light after driving at highway speeds on my 1997 XJ (AW4 auto tranny, 4WD) for 20 to 30 minutes. My XJ has 89,000 miles. The check engine light would not go out until I reset the codes with a code scanner. P1898 Manufacturer Control would be in the transmission control unit and P0700 Transmission Control System (MIL request) would be in the PCU (main computer). When the transmission control unit (TCU) has an error code, it communicates with the PCU and throws a P0700 to indicate that the TCU has a problem.



Recently I also started getting P0441 Evaporative Emission System Incorrect Purge Flow. and other Evap Emission codes (indicating a slight leak). I tried replacing the gas cap with a new one, changed the canister and purge valve, and checked the fuel vent lines and vacuum lines for leaks but didn't find any.



This has been happening for about 2 years and I had done the following without any positive results: change tranny fluid, clean tranny ground, replace cracked ignition coil (next to tranny ground), new neutral safety switch and new brake switch. I also checked the clockspring for continuity since I was having problems with my cruise control not working (was a bad brake switch). Some people have indicated that the 5 volt signal to the TCU or the tranny goes through the brake switch and the clockspring, but I have not verified that info.


This whole time my tranny and torque converter were working perfectly except for the codes.


What was wrong? The bundle of wires from the transmission comes up the firewall by the tranny dipstick and the ignition wire for the rear #6 sparkplug. The wiring harness was resting against the ignition wire. There was some electrical interference being transferred from the ignition to the tranny wires which caused the TCU to throw a code. There is also a bundle of wires in this spot that has the wires for the charcoal cannister purge valve. The spark plug wire had good insulation and a good boot.



I unplugged the wire harness connectors and moved the harnesses to the other side of the tranny dipstick, 2.5" away from the spark plug wire. No more tranny codes! I will have to wait longer to see if this has solved my emission code problems as well. The emission codes take much longer before they appear compared to the tranny codes.


I hope that this helps someone. I had searched online many times and never seen this solution posted anywhere. There are many reasons that the TCU can throw a code. If the tranny works fine and fluid levels are good, then check for this. It is a very quick repair.



Dave

Great job!!!!

Not solved!


The above listed repair decreased how often the error codes appeared, but they have come back, always on the highway. I tried swapping ECU computers in the engine compartment, but still got the tranny code.


I am going to order a solenoid service pack with all three solenoids and a new filter.


Posting this for anyone else dealing with this issue.


Dave

Update for anyone who will read this now or in the future.


I never did open the tranny, so I did not replace the solenoids or filter. My codes would almost always occur at 50mph or more. One time the check engine came on at 30 mph.


I had intermittent problems with my remote keyless entry module, so I replaced that with one from another XJ. The keyless entry uses the same data bus as the tranny control module. That seemed to decrease the frequency of errors but it did not eliminate the problem.


Finally Solved! I replaced Throttle Position Sensor and adjusted the brake pedal switch. Both items affect the function of the transmission and the brake pedal switch affects torque converter lockup. I have driven on the highway in high temperatures and have not thrown a code in 6 or 7 weeks. I believe that the brake pedal would bounce on the highway and turn off the torque converter lockup resulting in the DTC codes. It could also have been a bad spot in the throttle position sensor. To adjust the brake switch, push the brake pedal down and simultaneously pull out (down) on the center peg of the switch and it will ratchet out. Release the brake pedal and the center peg will get pushed back part way into the body of the switch. If the brake lights stay on with foot off the pedal, then push the center peg one click further in to the switch body. You want the center peg as far out (down) as possible without the brake lights staying on. Good luck to anyone having 1997 XJ mystery DTC codes.


Dave

Glad you got it fixed! Thank you for updating the forum. A lot of people never come back to explain how the issue was addressed.