My 2000 XJ with AW4 is always reading 100% TPS. I have tested 2 different TPS'es and both start with low ohms and sweep very evenly. Input V is 5.15 at the connector and the signal (output) at idle is .65, and gradually increases with throttle application. Yet when I hook up the Actern code scanned and read the sensor data it always shows 100%. I started looking at this because I have both P0122 and 123 (TPS voltage too low and TPS voltage too high). After clearing them they both come back immediately. There is nothing wrong with the connector. I had these codes and decided to replace the harness with a new one just to be safe. There was no change. Back when I replaced it about a year ago I only had P0123, voltage too high.

I am thinking this might be a faulty TCU since the TPS signal goes to the TCU before going to the PCM. The TCU is under the dash and since the engine tends to run hot I drive with the heat on all year long, even in summer, and have had the heat blowing down below by the feet. I am wondering if the TCU has kicked the bucket as a result. I know capacitors don't last forever and think maybe the excessive heat has caused some malfunctions with the di-electric break down, but that just might be me overthinking. The wiring harness that the TPS runs through got a lot of water in it and corroded/melted plastic badly and replaced that a few months ago, still no change. The parts that melted were the O2 sensors (upstream) and the gas-gauge. Since replacement my fuel gauge reads a little differently than it used to. It used to hit 95 or 100 at the mid tank level, now it's 85 to 90 miles.

It drives relatively normal as it always has although when warming up it will read lean (I have an AFR gauge on the dash) and gives me a 17-18 AFR briefly when accelerating from an idle for the first few seconds when not fully warmed up (and of course there is good hesitation with that), and can occasionally stall it out (I get around that by letting it sit in the driveway on for a few minutes and throttling it to let it warm up first).

Any ideas how else I could have two antagonistic codes about low/high voltage and still have a persisting 100% TPS reading on the code scanner?

 

What sensors are you using? If not MOPAR OEM I'd suggest trying that before replacing a PCM.

 

Both are MOPAR TPS. One is the original, the other I ordered from RockAuto, although it said somewhere on the box "Made in Mexico" so I don't know how much I trust that.

 

You can do 2 things

study the FSM, and fault find for a "while"

or buy a correct year TCM from the wrecker and replace it

imo, if you intend to own yr Jeep longtime, a spare TCM should be on hand

other OEM sensors can and should imo also be obtained this way

I think my spare TCM cost me $50

 

Perhaps if the harness got burned up resulting from the water damage it also burned up the circuit in the TCU or PCM that deals with the TPS. Like when people burn out an injector circuit in the PCM by shorting those wires while it is running.

 

Mopars parent companies have manufacturing plants all over the world. I'll reach past made in China so fast to get made in Mexico that it breaks my elbow.

 

Unplug the TCM and see what the scanner reads. I doubt it's the TCM.

There's a splice that branches the TPS signal to both the TCM and ECU. Check splice 112. It's easy. Just peel back the wire loom and dig for it. Here's a picture of where it's located. The wire color is orange with a dark blue stripe. You'll probably find it's uncrimped or it could be cut further down towards the ECU.

 

Good call on the splice. I would also measure the voltage at the pin on the ECU, and do a continuity check between that pin and the TPS connector.

 

Definitely do a continuity check. You're right on the money with that.

Based on the 17-18 AFR, I'd bet a dollar that he's got zero TPS signal going to the ECU.

On older carbureted vehicles, there was an accelerator pump that kept the fuel mixture right when you snapped the throttle. EFI doesn't have that. Instead there's the TPS. It tells the ECU how fast the throttle is bring opened. If it's not getting told anything, quick throttle operation can't be accounted for by the MAP and O2. I mean, the MAP can get pretty close, but it lags ever so slightly. And the O2 senses what's already been burned, so it lags way behind. That's why the TPS is so important. The TPS also inputs into the TCM, which helps tell it when to downshift. You can run with the TCM unplugged if you shift the transmission manually. You'll get (at the VERY least a P0700 code with the TCM unplugged)

 

Thanks for all of the advices from everyone. I was wondering about the splices. I looked in the FSM last week and was wondering where all these splices actually were. I've never seen one in a wiring harness and now I guess I know why if they're hidden under the looms.

I've disconnected and moved that large loom up at the top of the firewall a lot, and I lifted the hood in the back a few years ago to help with removing under-hood heat. I wonder if I will find some corrosion in there. !

I have a 2000 and the diagram appears to be a 99 and earlier judging by the intake and single manifold. These splice junctions are in the same spot? I guess I'll find out soon enough.

 

I didn't notice that, but yeah that's definitely a pre-99 manifold. I took that straight from the 2000 FSM though. Maybe Jeep just kept the same old pictures instead of updating them? I don't know.

 

I actually also have a P0715 (I think that was the number) for the Input Speed Sensor. I don't have torque converter lockup and think that has something to do with it. The FSM said that the TCU is to determine solenoid activation based on the differences in the input speed (the crank speed going into the engine) and the current wheel/MPH speed with the Output Speed Sensor. I have replaced the Input with 0 change with a NAPA replacement at a whopping $125 for that little thing. This is another reason I am led to believe the TCU is damaged since it all happened after I splashed into a massive puddle going down the highway (water got in that black connector at the back of the engine at the firewall with 14 pins in it, one of them is the TPS - I cut it off and put on a new connector with no change). The transmission started slipping to neutral and revving high immediately after I hit that puddle.. I had to pull off the road and let it sit for a few minutes.

I'm going to wait until I get the replacement Ebay TCU since I determined that taking the loom apart to investigate might not be the problem. I assume those splices are weather proofed. None of the loom is damaged so I find it hard to believe the splices would be the problem if that is the case.

 

New TCU fixed the hesitation coming off of idle, however I still have a 100% TPS reading according to my data scanner.

 

So how does it drive now?

 

I'm not sure how replacing the TCU (transmission control unit) would affect coming off idle? If your TPS is still reading 100%, I would check the wiring, in particular verify that the ground wire at the sensor is near zero volts.