Hi
Well, I have been doing some bragging over the last few months about our 2001 XJ8 being problem free (ie - no warning lights and no fault messages).

The other night my wife got stuck on a lonely country road about 4 miles from home and call me. I went there and we exchanged cars.

I had to drive the Jag in limp mode all the way home. Averaging about 10 miles an hour (30 mph going down hills and less than 5 mph up the hills).

I got P1121 fault code when I plugged in the code reader. I tried to reset the ECM by erasing the P1121 fault. No luck, just keep on adding P1121 faults.

I found several threads on the Jaguar forum that included P1121 fault. One thread mentioned the dealer replacing the Throttle Body to solved the problem.

I found one of forum member Gus thread (with photos) on cleaning the TB sensor connections (on Gus website: www.jagrepair.com ).

I looked at the Throttle Body R&I in the JTIS CD.

I followed its instruction to remove the ground battery cable as the 1st step.

Then remove the Air Cleaner Assembly to get access to the TB (just the 2 screws that attach it to the TB, then opened the Air Filter box and moved the Air Cleaner Assembly out of the way).

I also remove the engine compartment rear covers to view all the areas around the TB.

I cleaned the TB butterfly with Throttle Body cleaner. I also cleaned the TB sensor connectors (sprayed them with electrical contact cleaner).

I put everything back together. I reconnected the battery ground cable, turn the ignition switch to postion II (on position) and thank goodness no more fault messages (only Check Engine image). I reconnected the Code Reader and erased the P1121 fault code.

All is well again. Took it for a test ride, no problems so far.

I really did not like to do this type of work myself, but both of the 2 indy mechanic repair shops I use - were unavailable this week (one on vacation and the other swamped with too many other customers repairs).

I have a fear of breaking these plastic wiring connections. In the past, I have broken to headlight blub connector clip and a plastic holder for the bleed hose.

Hi Gus, I hope you do not mind, but I copied your TB sensor photos from your website into a 2 pages in a PDF file (so I could print all of them on a two sided page). I just edited the 2 pages to include a title statement giving you full credit and showing your website address on both pages.

Throttle Body Cleaning Photos.pdf

Jim Lombardi

 

only problem is a PPS(pedal position sensor) is on/in the gas pedal. The TPS(throttle position sensor) is on/in the throttle body. The terms are NOT interchangable. They refer to 2 totally differant sensors

 

Hi Brutal
I know that it sounds like I am giving incorrect information, but look at this other forum thread (it has an August 2008 date) and it mentions the car dealer replacing the Trottle Body to fix the P1121 fault code:

https://www.jaguarforums.com/forum/x...de-p1121-7951/

I was not sure if it was correct, but cleaning the TB and its connector plugs did fix my issue and I did have a P1121 that put the engine in limp mode, trac and cruise trouble message and ecm displaying engine symbol.

I called one of the indy mechanics and told him that it was a P1121 fault code. He said it could not be the pedal position sensor or it adjustment. He also said I should just erase the P1121 and see if that fixes it. It did not fix it, in fact I keep finding the P1121 coming back every time I erased it.

After I cleaned everthing (TB) and was able to start the engine without all the trouble messages. I erased the P1121 and it has not reappearred and the check engine ecm symbol is gone.

Thank goodness.

Jim Lombardi

 

The PPS is not in the throttle body in an XJ8? That's odd- The connector with the wire colors shown in the manual sure connect to the pedal actuated side of the TB on an AJ27. If it is not there, then where is it?

 

a pedal position sensor is for the gas pedal, the throttle has a throttle position sensor. You push on the pedal and the PPS sends a signal to the ECU which then sends a demand to the throttle motor to open or close the throttle. The ECU refferances where the throttle is by the TPS. You can have a code for 1 or the other or both. But each sensor has redundant tracks. If there is a discrepancy between the tracks it goes into limp home mode(next time push the pedal to the floor youll get more than 10mph.)
The ECU knows which sensor threw the fault. But you can have a disagreement between sensors and have a fault that flags incorrrectly to the TPS or PPS when the other sensor is really causing the discrpancy. I dont really know off the top of my head what the P1121 is really for. Also, The reason I jumped on this thread is because Ive seen a throttlebody replace for a PPS code and visa versa. Sometimes techs dont think or see what theyre reading and thinking a TPS when in fact its PPS. DO NOT confuse the 2. Many times a code like this is not constant like yours. And it will set limp home immediatly if a discrpancy is seen. There obviously is NO room for error on fly by wire throttles and gas ppedals..... But you may not be able to repeat the fact when datalogging or scoping the track signals in each signal....Did I just make it clear as mud or do you understand now???

 

Brutal:
I understand and concur, but I want to be clear- The PPS is physically located on the side of the TB, behind the part that the throttle cable attaches to, right?

 

A good clean up worked marvels , awesome .This is really good

 

I would also like to understand the sensor location - since the Throttle body has more than one.

I just assumed that the PPS was the sensor on the TBody by the gas petal cable spring at the TBody and the TPS was on the other side of the TBody by the Throttle motor. Does the car have a sensor in the cabin?

I had a restricted performance issue -- and did nothing at all --- the fault did not come back for the better part of a year. Early models did have TBody issues and contact problems at the TBody - but I am not so sure this is the issue that many of us are having.

When I looked over my connections all of them were spotless -- and I have not had another RP event.

 

@ Yeldogt - for the AJ27 TB your description is correct - I think Brutal may be mixed up with the later x350 model?

I had a recent event P1121 and as directed to the throttle pedal, the only thing connected was the brake/cruise double switch, swapped for a new one, and still got the P1121.....

I then swapped the spring PPS part off a known good TB onto my car, hey presto all good.

It seems cleaning connections can cure it, sometimes.....biggest problem is getting a PPS on it's own, no dice from Jaguar, so it's a second hand TB. The other side of the TB where the TPS is shouldn't be messed with, fine to clean connectors, but not to disconnect or remove the TPS from it's factory set position, the ECM doesn't like it.

The PPS has tracks that get worn over time, once the signal breaks down it posts a fault immediately - I've actually watched this happen by removing the induction tube, watched the OBD monitoring the pedal position, as I depressed the throttle pedal slowly the percentage went up as it should, then dropped to zero, the butterfly then stopped opening. At this point the car does not know where it should be, bang failsafe mode.

If the car is high miles this fault is more likely to happen. If it's low to average miles, it's more likely cleared with cleaning the sensor connection.

 

No, and now that Im at work today vs at home last night. That code is for I quote "TP sensor" throttle postion, not a pps pedal position.
The TPS is on the side of the throttle body. again the PEDAL POSITION SENSOR is in the gas pedal assembly on fly by wire cars. Now since this is not a fly by wire car then yes the pedal position sensor is on the side of the TB below where the cable is connected youll see the connector. JUst dont confuse the 2, they both have 2 tracks in them and compare signals.if there a discepancy youre into limp home. On cabled cars if you push the gas pedal to the floor theres a mecahnical overide that you let you do a good 60-70mph as it gives you a 20% throttle opening. Now the issue becomes when peopl with the later fly by wire cars see a "I fixed my PPS issue with a throttle body" they need a GAS PEDAL assembly

 

Can you tell me whereabouts exactly? And what years are we talking about? Cheers!