I have a persisting 122 and 123 on a 2000 XJ Classic for several years now. I have replaced the part, and replaced the wiring harness connector with no change. As far as I know that wire runs to another connector that then runs into the TCM and from the TCM back to the ECU. THe ECU and TCU are in pristine order, although I recently had water get in that secondary connector between the TPS and TCU; However I have had these codes long before that. THe connector was fixed and replaced by me personally a month ago, and the TPS wires/pins weren't harmed by the water damage (just the O2's and the gas gauge). The TPS operation has seemed off for quite a while as I am accelerating there are 2 brief spots where it loses a little power for a second while accelerating hard. I just tested both sensors with a voltmeter to verify smooth changes in the signal as the throttle is slowly moved so the sensors aren't the issue unfortunately.

I don't know what else to do at this point. I need some recommendations to give me motivation to find a fix for it.

I also have a P0715 for transmission input speed sensor. This code came up after I hit a massive puddle on the road to work one day (the same time that connector got corroded, but the Input Speed Sensor isn't in that connector at all) and I have since replaced that part with a brand new one from Napa for $120 with no change. The problem I have now while having that code is that I do not get Torque Converter Lockup. The way I understand those input and output speed sensors is they are both referenced to determine which gear for the transmission to be in based on engine speed vs wheel speed. The connector and harness looks fine, although I looked in the FSM and it doesn't even point these connectors out on the transmission. The wires run to one of those 3 harnesses by the back of the engine but they all look fine, and I see no damage on the wire itself by the transmission.

EDIT: Just cleared the codes and both the 122 and 123 for high and low voltage came back immediately. I am thinking about swapping out the TCU with another once I've had for a long time.

 

Here's a better question, How is it possible to have BOTH a 122 and 123 at the same time? One is for too low voltage, the other is for too high. I reset the codes and both came back instantaneously. When I check the voltage with a multimeter with key-on vehicle off I get around 5.15V so the 123 makes sense there.

The spare TCU I had wasn't the same as the one on my 2000 so that was a no-go. I took it apart and inspected it and it looked perfectly clean inside and out, as well as the connectors.

How can I possible get extra voltage to the TPS? I'm guessing a slight short from another circuit but I don't know how that could be since the wiring harness connector for it (which I just cleaned/replaced) is now immaculate.

Edit: Checked +/-/Signal voltages at Key-On Eng-Off, and Key-On -Eng-On.
Positive lead is .63V KOEOff, 5.12V with KOEOn
Signal is .63V KOEOn, same with engine off (gradually changes with throttle increase).

HOWEVER... when I plug in the OBD-II scanner and check the TPS signal from there it registers 100% TPS all the time, and I know that's not right as I've looked at it in years past. It's 100% at idle, part throttle, and WOT.

I have 2 TPS sensors and both are the same read out. Seems like something between the TCU and PCM, or internatl to TC / Internal to PCM is off. Next I will remove the fuses for the clock spring thing as I have seen that can cause faulty TPS signal readings. My Airbag light has been on for years and the clockspring has been broken longer than that.

Edit 2: Nope. Pulled horn and air bag fuses, motherfugger is still fuggin' mothers at 100% readout to the scanner. D=