A few weeks ago I bought my first ever Jag, a 2003 Jag XJ8 (The X308 type) and it has not been without the standard slew of problems, you know, to remind you it's a Jag...

Anyway I am having several of problems, which may be coming from one or more sources, and I want to try to diagnose and repair the problems with as little collateral damage as possible. I love the car, but I know I cant afford to bend over before a Jag dealership, especially not in this phase of my career (I'm not even graduated yet!). I'm a mechanical engineer by trade, and so I am more handy than most, for whatever it's worth.

Anyway, I bought the car with the ABS light always on, and the "TRAC/ASC" message on. According to the previous owner, the traction control was fritzy, and so it occasionally would be on and off, but it now seem to be solidly off. I have been reading about the causes of this problem, such as a dirty wheelspeed sensor, bad battery, or bad ABS module, all of which I will be looking into more deeply in the near future. Another issue I bought the car with was an exhaust leak.

I drove the car for a while, when all the sudden (when accelerating into a left from a stop), I had a gearbox fault and an engine failsafe, prohibiting me from driving at all. I had it towed, and brought it to my local mechanic, who basically reset the computer and the engine ran fine (which confused the heck out of me at the time). Also, while it was in the shop, I had him weld the exhaust leak.

Since then, however, I couldn't help but feel that the car was down on power from when I was driving it. I have been reading and contemplating, and I have the following two theories:

1) welding the exhaust effectively reduced power from when I was first driving it due to backpressure mufflers typically create, or

2) the TPS is somehow out of calibration, and my engine literally isnt revving as high with the same depression of the throttle. I was hoping someone who drives the same era model of jag could help me to prove/disprove this. When I am accelerating from a stop, full throttle (literally pedal to the metal), I watched the tachometer and saw that the RPM would only peak at only just over 4k before gear-changes. I never got to know the car too well before this happened, but this does seem low to me, does anyone disagree?

The gearbox fault is known to be triggered by a faulty TPS, but I am not completely why it would have regained functionality after a reset, as I was under the impression that the TPS fault was a more fatal condition. I thought the potentiometer in the TPS was out of calibration, so I tried resetting the computer (disconnecting the battery for about 5 minutes), no good.

Anyway, if you have actually read this far I already sincerely appreciate it, and if you have any input to make to any of my woes, I would appreciate it even more.

 

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The first thing i would do is clean your battery connections , including the ground connection from battery to chassis.

All my faults disappeared after doing that.
Drop in a new battery to , if your not sure about it's state.

These cars are utterly sensitive for low voltage on the ECU and other modules.

 

I agree with Popeye. Before you dive too deep, check for items that can lead to low voltage. Search for "low voltage" in this forum and you should find the usual suspects. . . battery, battery terminals, battery ground strap, megafuse behind spare tire, wiring terminal under tool tray on passenger side of engine, ground strap under the car inside passenger tire and behind engine. . . Check for melting, loose connections, rusting, etc. It could be an easy fix!

 

Hi

I found this hard reset information in a forum post (member DavidN):
Do the hard reset to re-calibrate the TPS.

- Disconnect both battery cables from battery
- Turn on ignition
- Turn off ignition
- Connect battery cables together
- Turn on ignition
- Turn off ignition
- Reconnect battery cables to battery
- Start the car
- Let it idle for about 10 Minutes

(Got your radio code? )


It temporarly fixed my check engine problems (displaying gearbox, ABS, Trac, ASC faults, failsafe, etc) a number of times. At least it got me out of limp mode (after hard reset and using my Code reader scan tool to erase fault codes). I was able to drive at normal speeds back to my home. Now I always have a small travel tool kit and the code reader scan tool in our 2001 XJ8 trunk (boot) just in case we have a problem.

Jim Lombardi

 

Not sure about Jag, but on Land Rovers the idle will start to be erratic when the TPS is going out.

 

Hi
Update - I posted the TSB 303-S498 in the Sticky TSB thread a few minutes ago:
https://www.jaguarforums.com/forum/x...20/#post418954

I have been having issues with the throttle body. I had a P1121 DTC fault about a month ago. I cleaned the throttle body and all the sensors that plug into it. Then I used my code scanner to erase the DTC. That solved the problem for a whole month.
Now we have a similar issue that started 2 days ago - P1642 and P1122. My indy mechanic had me order 4 TPS harness gold connectors per TSB S498. The part number for 1 of these harness connectors is LnG3956AA.

I placed an order with Nalley Jaguar (list price is $17.50 each). Nalley gives us forum members a 25% discount and free shipping (total cost for 4 parts is $52.50).

You should look at forum member Gus DIY on Tboddy (it has a reference to the TSB S498):
Jaguar throttle body cleaning xk8

This is the direct link to the PDF file on Gus website -
Gus has a number of preliminary webpages that you would to go through before you would get to this webpage.

Thank you Gus for this information - I appreciate all your efforts.

Here is another DIY on cleaning TB and MAFS (PDF attached failed, so I copied PDF to my mediafire account):

DiY_Document_Clean_MAFS.pdf

Jim lombardi

 

All of the above is good advice. On the acceleration thing, have you tried putting it in "sport mode" ? The little switch on the shifter surround with an "S" on it. When mine is in sport mode (all the time), and I put pedal to floor, the car goes to 6800 RPM for each shift - although I've only been able to do that up to third gear due to the risk of being arrested by the cops. :^)

 

Alright, due to my busy schedule, I can only try things in small windows I have throughout the week, so here's what I did so far:

So I checked my battery terminals, and the chassis, ground, flawless condition. I measured the battery voltage, 13.7v running, 12.4v off, exactly what one would expect.

I also removed each wheel speed sensor, cleaned them, wirebrushed the brass ring/washers on them (they were a bit corroded, and I wasn't sure if it was an electrical/ground contact) and put them back. They weren't terribly dirty, and so I wasn't surprised when the problem continued to exist despite clearing the error codes.

I want to try the more elaborate method of clearing the battery, in case there was still stored charge. However, its worth noting that I have had the battery completely disconnected for some time, and I have never had to reset the radio code, and so I am not sure if that means I don't have to, or if that means I did not successfully reset it before.

 

Thanks for this. FYI, yes, it was in sport mode, so I can say quite definitely that I am down on power. (I am not just making it up in my head... now that my car is so much quieter, and might "feel" weaker)

 

julio -
I think I remember reading somewhere on this forum that North America spec cars did not require a radio code. Though by messing around you could reset it so that it WOULD require a code!

 

Alright, here is an update.

I went to go try to do the ABS module fix (Welcome to Jag-lovers - Members Photo Viewing Page), and when I realized I didnt have the proper tool, I took the car out to get it and I had another gearbox fault/engine failsafe.

Had the code reader with me, and it had P1122 (Throttle Position (TP) Sensor Circuit Intermittent Low Voltage). This had happened before, and so I cleared the code, and drove another mile before getting a P1121 (Throttle Position (TP) Sensor Circuit Intermittent High Voltage).

So I reset again, and tried (successfully) to get home. The throttle was acting very finicky the whole way, seeming accelerate irregularly and twitchy the whole way, exactly what you would expect from a bad TPS.

So, on a purely minimum cost basis (again, im not afraid to get my hands dirty), what should I do to mend this?

 

Hi juliovega914
We had a P1121 fault code about a month ago. I cleaned the throttle body butterfly and a couple of the sensor plugs and connectors (with throttle body stray cleaner and electrical spray cleaner). Then I erased the error.

All was well until about a week ago, went into limp mode with P1122 and a P1642. Our indy mechanic made a few calls and recommended changing the TPS electrical connectors (mentioned in TSB 303-58).

I called Nalley Jaguar Parts and they gave me the part number for the wire with the new TPS electrical connector (connector tip has gold in it versus the old style tin one).

You need 4 of them and Nalley has them on the shelf. Part number is LNG 3956AA (gold terminated cable). List price is $17.75 each - Nalley gives forum members 25% discount and free shipping on orders over $25.

Steve Prichard from Nalley found TSB 303-58 and email it to me .


I posted the TSB 303-58 in the TSB sticky thread. Here is the link to the PDF file (TSB 303-58):

https://www.jaguarforums.com/forum/a...tsb-303-58-pdf


After our indy mechanic replaced the 4 wires, the engine idle smoothen out (was somewhat rough before the repair).


2 days after I had a problem with holding the ignition key in the starting position over 5 seconds (engine seem to be taken a little longer time to start then usual - maybe I was imagining it?).

Anyway the check engine went on and techometer starts goes up to 2000 RPM then down to 0 and up again.


The scanner gave me a P1638 (CAN INST token message missing) - montioring condition is ignition ON > 5 seconds. Well that was exactly what happened. I held on the ignition key on too long.

I used the scanner to erase the fault and all is well again.

My wife and I getting a nervous about the number of limp mode faults we have been getting over the last month or so.

Well the the more issues we have with the XJ8 then the more we learn about how to fix them.

Jim lombardi

 

Julio: Quick fix? Clean both sides of the TPS connector contacts with spray contact cleaner/lubricant from Radio Shack (or equivalent). I haven't had an 1122/1121/failsafe mode since I started cleaning these - I do so at each oil change now. Previously they were occuring several times a week.

 

So I tried QuadManiac's solution, and I also did the complete ABS repair as detailed here: Welcome to Jag-lovers - Members Photo Viewing Page

Problem is, it didn't do anything =/ Gearbox fault still happens every so often, and the ABS light and ASC/TRAC message still goes by. Gotta be honest, I feel pretty defeated by this, I hoping at least the ABS module fix would have worked.

Just to note, I don't receive any error codes (besides p1000 and p1111) at any point, except when I am having the gearbox fault where I usually get either p1121 and p1122.

 

sounds like its time to change the throttle body?

 

I was thinking the same thing- Ouch!

 

The gearbox fault will be triggered by the signal breakdown from the throttle to the ecu.

Nothing wrong with the gearbox, and you've fixed the abs.

It's time to sort the throttle, ring around breakers yards, also register online with a parts finding service and wait for the prices to come in, then its time to haggle.

If you where in the UK I'd send you one to fit to see if it cured it, but having read through your issues, it really looks like the tps and or the tpps are breaking down, and you can't get the sensors, it's a good second hand unit or new, yep, Ouch!

 

Wasn't there a company who sold rebuilt XJ8 throttle bodies for the order of 750?

Frankly, I don't want to pay 2500 for a brand new one, but at the same time, buying a used one on eBay doesn't guarantee the TPS isn't just as ruined as the one I have... since it seems they all die after about 70k. So rebuilt is best IMO.

 

Don't worry too much about the ABS, I'm sure you have it fixed if you accomplished the soldering correctly. The rest is surely the throttle body. There are a couple of outfits out there that can help. One is JayTan Industries and the other is Auto & Truck ECU, I think. I've use JayTan a few times. Had a couple of rejects, but they always made good on it quickly. Your car is a 2003, so it should already have the gold terminals on the TPS, that means it must really be a TPS fault; that requires a throttle body rework or replacement.

Good luck!

 

I bought and installed a JayTan throttle body, and it seems to be running a lot better now. No gearbox faults yet, and its been a good week. I also replaced my thermostat housing with an aluminum one when I was at it. Great improvement overall.

The problem is that my ABS light is still on with the Trac/ASC signals still coming up. Its a bit of a mystery to me at this point.