[I posted this tread on french forum "sovejag" on Sam 21 Oct 2023. I am sharing now here.]

More and more often I get a P1222 error:

P1222: Low voltage on pedal position sensor circuit "B

• Low voltage between pedal position sensor and ECM sense circuit "B" (sensor pin 3), open circuit or high resistance
• Sensor power supply fault
• Failure of the pedal position sensor

Be careful not to confuse the TPS (Throttle Position Sensor, right-hand side of throttle body, does NOT concern my fault P1222):



and the PPS (Pedal Position Sensor, left side of throttle body, is related to my error P1222):



I undertook to remove and open the PPS for internal diagnostics.

I preferred to remove the complete throttle body first to be comfortable.

Then I separated the PPS case from the throttle body. I realised afterwards that this wasn't necessary to access the inside of the PPS. I'll detail the procedure anyway:

You need a T35 torx safety bit (i.e. the bit has a hole in the middle of the star):



When reassembling, you need to hold the butterfly (inside the butterfly body, on the left in the photo) completely closed with your hand, so that the 2 tabs (indicated by the red arrow) come into contact:

• The tab (on the left in the photo) must be behind.
• The tab (on the right of the photo) should be in front.

The throttle body is seen in the photo from the front of the vehicle.



Let's move on to the PPS sensor. Remember that the step in the previous image is not necessary, you can open the PPS sensor without separating the PPS box from the throttle body.

You need to undo a 10 mm nut and remove the throttle cable lever and its spring.

Then you can undo 4 screws (Torx T25 safety screws) and remove the PPS sensor cover:




The white part of the sensor (in the middle of the photo above) contains the various PPS sensor tracks. They appear to be in good condition.

The black sensor cover (on the right in the photo above) contains the brushes.

There are 5 static brushes (on the right in the photo above) which provide the (fixed) contacts between the tracks and the external connector.

There are 3 pairs of moving brushes (see photo below) which have "hairs" at the ends.

You can see that the top pair of brushes is very worn and has almost no hair left. You can see some debris in the lid.




I've come up with 2 theories to explain the greater wear on the top brush:

• There are 2 concentric shafts, the top brush is not driven by the same shaft as the other 2 brushes. Would the top brush move more frequently than the others (I'm not convinced when I look at the mechanism)?
• The top brush describes an arc of a circle with a much larger radius than the other 2 brushes, so it covers a lot more distance.

On the forum, a colleague found a Toyota PPS box that he said would fit his 2001 xj8. It's a 3 screw box and a 4 contact plug so it won't fit my 1998 supercharged (4 screws, 5 contacts).

He doesn't say whether he went through with it, so we don't have confirmation that it works. He says that at least the throttle lever and the junction lever with the throttle body are not identical and must be taken from the PPS jaguar.

https://www.jaguarforums.com/forum/x...option-252002/


As for me, I'm asking this company if they can take care of my repair (unless someone has another lead?):

https://autoecu.com/.

In the meantime, I did what I could by adjusting, with tweezers, the shape of the defective brush to use the shorter "hairs" that are still attached to the tip of the brush.



I reassembled everything by checking my Pedal Position Sensor (PPS) curves at the IDS:



The road tests were conclusive, the pedal responds well and I did 7000 kms in 5 months without a problem, until the problem returned, see next post.

 

As I said after a few month, my makeshift repair has again started to show signs of weakness in recent weeks (acceleration not so good), and then in the last few days code P1221/1222 Pedal Position Sensor.

This time I thought I'd try a transplant.

You remember I warned that my issue was not the TPS but the PPS. Well, I ordered a TPS anyway (for a dozen euros):



Using a hot air gun, I opened the TPS to canibalise the potentiometer brush:



I recovered the precious brush (a few hairs got crossed on the left brush but I put them back in place by "combing" them with the point of a needle):



The new TPS brush holder (above) doesn't have the same base as the PPS holder (below) so it's not easy to reuse as it is. Never mind, I removed the brush holder from my PPS, cut out the 2 damaged brushes and welded on the new ones from the TPS (with my old eyes, I can only do all this with a watchmaker's magnifying glass):



Replacing the reconstituted brushes in my PPS:



My road tests were perfectly conclusive. The future will tell if it holds up over time. It's hard work, but if you don't want to try the adventure of a second-hand car or a US restoration workshop (autoecu never got back to me), there's only the choice of a new throttle body at ~1200€.

I'm aware that if this kind of repair fails under full acceleration it can be dangerous, so here goes, take it with full knowledge of the facts.

 

That's great work! To find a solution like this on a part that 100% fail at some point, I just wish the AJ27 had a fix like this, it potentially has now you've opened it all up - I will have a look at the 27 throttle and see what can be done.

 

Hi Sean,

Ok, good luck, and let us know. So far my second repair (transplant) still works good.

Bruno