Finally got my buddy to agree to take his 02 XK8 out for a winter drive to breakfast. Picked a half way meeting place, then drive together from there.
My wife and I got there a few minutes early, I switched off the engine.
My wife asked what's that burning smell? Hopefully I said it was from the outside since we didn't seem to be burning. Appears smell went away fast.


My buddy arrived with his DD, as the his Jag was having battery problems.
Sounds like an omen.


We decided to just go to a close by eatery. I gave Dave the key to our car and told him to drive. He started it up and asked why the engine was running so rough. Damned if I know, I told him. Never had that problem.
We started to drive, and he said he had the pedal to the floor and the car would only go 10 mph.
Pulled over and had the DSC message.


We still went to breakfast, and we limped the car 10 miles home.


Have an old Autoxray scanner and wasn't sure if it would work.
It did give me a P1251 code which is throttle position according to a post I found on this website. Also gave a P1657 code, which I couldn't find.


However, when the code reader was in the system the car's info panel also gave a "Gearbox Fault" message. It did not display this when reader was removed.


Had problem a while ago with the Sport switch, which we removed and thought it was fixed, but it has returned to it's problem of staying out and engaged with the light on. When the scanner was plugged in, the sport mode light went out, then went back on when scanner was removed.


Any ideas out there.


Much appreciated
Jack

 

All the codes are here: X103_P_DTC_OBDII_R1.pdf

They both seem to point to a throttle body relay. Seems like a good (and cheap) place to start.

Best of luck, keep us posted.

 

Update; still looking for advice.
Checked throttle motor fuse....OK
Removed air plenum, turned on key, pressed throttle, and throttle plate does not move.
Can motor assembly be rebuilt if that's the problem?
Thanks
Jack

 

I would first look at the battery voltage and then second check your grounds. Yes the throttle body can be checked and repaired if necessary. The company I have been using is ASI and I will provide a link for them.

Link http://www.autoecu.com/index.php?p=1

 

The code book mentions the relay:

POSSIBLE CAUSES:
Throttle motor relay coil power supply circuit: open circuit (fuse)
Throttle motor relay failure
Throttle motor relay coil to ECM circuit: open circuit
ECM ground circuit fault (relay coil drive)

and
Throttle motor relay failure
Throttle motor relay coil to ECM drive circuit: short circuit to B+ voltage

The complete diagram is in here, Fig 04.1.

jagxk2003.pdf

Same book has the relay locations on P21. Seems to be by the brake booster.

I would definitely check the relay, and any wires leading up to it. I would take a hard look for any burn marks as you reported a smell. I believe the general advice is to swap out the relay with the same model from somewhere else in the car for diagnostic. Obviously, double check before doing this.

Best of luck, keep us posted.

 

All appears to be well


We had snow last night, so don't want to do a road test until roads are dry.


Made some calls to a friend who works for Factory Five and is knowledgeable in the workings of engine electronics.
Based on the code readings, he had me remove air plenum so I could see the throttle plate.
With my wife in the car with key on, engine off, I observed as she pressed the gas pedal. Throttle plate did not move, so now we had a starting point.


Thanks to the link posed fmertz, I was able to download the wiring schematic and locate the throttle motor relay. Was set to exchange relays if necessary to see if relay was at fault.


When I removed the relay cover (2 relays under that cover) it appeared that the throttle relay was not fully plugged in. Question was, was it loose, or did I loosen it when pulling up on the cover.
Seated the relay, and turned on key. Still had a fault notice, but engine started, ran smooth, and there was throttle response.


Shut off engine, called my wife to repeat throttle check, and plate moved when she pressed on gas pedal.


Have to read the my code reader manual on how to clear codes, and it looks like all is well (for now).


Thanks again for this forum and to the members who were able to help.


Maybe this is a good time to check the seating of all the relays.


Cheers
Jack

 

If it were my car I would check it all.

Gus
www.jagrepair.com

 

Clearly, someone has been there before, so this could be a recurring problem, possibly unsolved. If it was me, I would definitely order a new relay, and keep looking around. Cleaning all throttle body connectors with contact cleaner would not hurt either. The cost of a relay has to offset the potential aggravation of driving home some distance in limp mode.

Thanks for the update. Best of luck.

 

Good points
Going to check all relays for proper set.


What is interesting is this car when we purchased it last fall had to be one of the cleanest and best cared for 40K mileage vehicle you could ask for. It was a one owner car and spent most of it's life in Florida only being transferred to the owners Northern home recently.
Engine compartment looked like it just came from the factory, but that of course doesn't mean that somewhere along the way someone had removed the relay cover and disturbed the relay, or maybe it was just the Jags way of keeping me humble and on my toes.


What I have added to my owners manual case, is a printout of key wiring sheets and info from the wiring website that you thankfully supplied.

Thanks again
Jack

 

I'm sure everyone has done this, but being a Seasoned Citizen and just semi-proficient with a computer, I have put the link to the XK8 wiring schematic in the favorite section of my iPhone, so now the complete wiring for the car is just a click away.


Not sure yet if I'll carry the code reader in the boot yet!!


Jack