Hi. I have an S type 2004 (I just got it a month ago). It has lpg installed along with gasoline. It used to run well on lpg, but poor on petrol. There were temporary issues when it was raining. I got an odbc reader and erased them. A week ago it was on idle for about an hour. Then P2135 came on. I delete it, but when I turn the ignition to the on position (no start of the engine) it is there (as a pending fault - limp mode without starting the engine at all). Also no power on fuse f18 (throtle- the limp mode might be causing this). Cleaned the throttle body and the TPS contacts, "dried" TPS for possible water. No improvement. Reader indicates at idle throtle position 9% and it sometimes changes to (-0.4%). Any ideas please?

 

It's not faulty for it to read 9% or whatever.

I gather that code indicates a problem with the TPS. See http://www.jaguarforums.com/forum/s-...roblem-163451/

If you have a fuse problem then fix it first. After that, I would treat your car as being like a 2005 but not like a later one (because the later ones have a different PCM and thus different software).

Note that the TB and TPS are high-precision devices which can be upset.

 

Thank you javV8. There is no fuse problem. There is no current going to that fuse in the fuse box. I assume it is the ecm blocking this due to limp mode. Also, it must not be the pedal. Limp mode comes on when I just turn the key, before I start the engine or press the pedal. Is it possible that needs refreshing for the pedal adoption? Or maybe water is causing a short of some kind?

 

If it was the throttle body or the TPS, shouldn't the limp mode come on once I start the engine?

 

Who knows? Why even think that way????

 

This may be normal, depending when you are testing for power at this fuse. Was the voltage reading taken with the ignition on or off?

Wiring diagram here, scroll to figure 03.1:

http://www.jagrepair.com/images/Auto...x2062004en.pdf


Fuse F18 (at the front power distribution box) is shown next to the throttle motor relay R4. When the ignition is off, that relay is relaxed and you will have no power at the fuse. So if you checked for voltage with the ignition off, no power is normal there.

Also, to clarify, will the engine start? When I first read your post, I was under the impression the engine would not start. After reading again, I'm not so sure. Big difference on how to troubleshoot, so I'll wait to hear back.

 

Fuse f18 has no power on all cases. Relay is ok (exchanged it with a proven good one).
Engine starts - although in limp mode.
So basically what confuses me is this
There is an error code causing limp mode. I do erase the code. I turn of the key, take it out, even disconnect the battery ... no matter what I do, when I turn the ignition to the position on, limp mode is there, before I start the engine.

 

Yes, there is a fault (as shown by the code) that is there all the time.

 

True . But since I delete the error with a diagnostic, I would expect it to appear again once I start the engine. So I am thinking maybe there is a wiring problem.

 

Thanks for the clarification about whether the engine starts.

Good troubleshooting to swap in a known-good relay. For the next step, I'd suggest a click test to confirm if this relay is getting the command to close. Hold your finger on this relay, and have a helper turn the key from Off to Run. You should feel the relay click, which tells us it received the command. If you don't feel the click, try starting the engine just in case turning the key to Run wasn't enough to send the command.

 

Worst case, refer to the code in https://europeantransmissions.com/Bu...C-jag/obd2.pdf

 

I will try this tomorrow and come back.

 

Relay doesn't get the command to send current to the fuse (possibly due to the limp mode). But I think I found something. The power supply to TPS is 4v instead of 5v. This has a result to signal voltage as well. Any ideas how to access the wiring to the PCM?

 

Or maybe a wire harness before that. Any idea where MAP sensor and/or IP sensor are located? They have the same power supply line according to the diagrams.

 

Ooh, excellent find! That could easily skew the sensor readings.

Looking at the wiring diagram (2005, fig 03.1), this same +5VDC reference signal feeds six sensors. Towards the right of the page, see splice PIS22 for where the circuit branches out. The six sensors:

TP1
​​​TP2
​​APP2
FTP
MAP
IP

While monitoring the voltage, unplug these sensors one at a time. If the voltage returns to normal, that means the one you unplugged was drawing more current than normal. Not enough to blow a fuse, but just enough to affect the other sensors on that circuit.

Fingers crossed!

 

In case the wiring is behind the bumper or even up in the wheel arch (aka wheel well), it may be harness damage.

The bumper harness is a known problem area for some MY cars.

 

Thank you all for your help. Once I resolve the issue, I will post the outcome. So, it might be of help to someone else for future reference.

 

Hi there. Just an update. I took the car to a jag specialist. (The car is RH - UK model, but I live in Greece - not many jag repair shops over here). He just called me. He said that after 3-4 hours of diagnosing the car, he spotted that although 4.9 volts leave the ecm, only 4.1 arrives to the TPS. So, there is a short somewhere in the way. Tomorrow he will try to locate where the shortage is. If he will have no success, he will have to replace the whole harness. I am actually thinking of suggesting to him to just replace the specific cable.

 

Did you or your mechanic try unplugging the sensors one at a time as suggested in post #15 above? This won't cost anything to try and may lead you straight to the fault.

There may not be a wiring fault at all. The 5v reference voltage feeding each sensor is typically VERY low current. In that case, the wiring can be also be very small (to save money). But if the current increases too much, this previously adequate wiring suddenly can't handle the increase. The wire run now acts like a long, skinny resistor. There's likely nothing wrong with the wiring. It's just being loaded beyond capacity. This could easily explain the almost 20% drop in voltage you have experienced.

As you unplug the sensors one by one, the current flow will hopefully drop back to normal. With any luck, the voltage should recover right around 5.0v.

I read up a little about how the TPS works. From what I understand, it is likely to be the first to set a fault code due to low reference voltage. The other sensors are single channel. If the reference voltage is low, those sensor values will be correspondingly low, too. But with the MAP sensor, for example, If the output was 20% low, the poor computer wouldn't realistically be able to know it was inaccurate, thus no fault code.

But the TPS is unique. It is two sensors wired inversely, to crosscheck each other. I'm going to use percentages instead of voltage just to make the math easier. With the throttle plate fully closed, one channel will be 0% and the other 100%. When fully open, the values swap and the first channel will be 100% and the second 0%. At one third open, it's 33% and 67%. At two thirds open, it's 67% and 33%. Note how the two values always add up to 100%. If they dont, the computer interprets that as a problem with at least one side and sets a fault code.

What happens if the reference value is low? If only 80% of normal, you'd be adding 0% and 80%. Hold the throttle wide open, and you'd be adding 80% and 0%. No matter the position, whether fully closed, open, or anywhere in between, you'll never get the values to add up to 100%. I think this is why you're getting the fault code as soon as you turn on the ignition. The computer senses a major problem and tells you right away.

Please remember the computer is simultaneously very smart and very stupid. It doesn't have any way to check the reference voltage way out at the sensors. All it can do is respond as programmed. And certain faults can cause a code that may seem misleading.

The accelerometer pedal position sensors (APP 1 & 2) are wired in a similar inverse manner, but with one important difference. The two sensors get their reference voltage from different circuits. If only one was low, and it was the sensor at 0%, the other sensor (with the correct reference voltage) will be at 100%. So even though one sensor had a low reference voltage, the outputs would still add up to 100% when your foot is off the pedal.

With either dual sensor (TPS or APP), dirty internal contacts would also prevent the values from adding up to 100%, and you'd get a fault code. But since you have already confirmed low reference voltage at the sensor, I don't think dirty internal contacts is the problem. I think one of the sensors (could be any, not just TPS) is drawing too much current and pulling down the the reference voltage. The only confusing part is this may be misinterpreted as a TPS fault.

 

Very helpful all advises. The repair man didn't.. repair 🤣. He probably did nothing. He told me to change the throttle assembly because there is no power in the throttle motor!!! Anyway what I did is this. I unplugged most of the sensors (I couldn't locate the FTP sensor - although I took off the rear seats). No difference in the voltage. BUT, when I tried to reach the Fuel injection pressure sensor, I couldn't reach it. I moved the wiring a little (mostly the part that goes deep down to the back of the engine) the voltage "moved" up and down (by the way this area is exactly where rain enters the car). Tomorrow I am planning to go to a pure car electrician and ask him to check it -while I am present). I am thinking that maybe the car has to be lifted to gain access to that area.
P.S. One interesting approach I found to similar problem is https://www.motor.com/magazine-summa...nder-may-2016/
Maybe it will be helpful for someone.