Dear Jaguar Enthusiasts,

My 2002 XKR has suffered several incidences of the dreaded Failsafe Engine Mode, ASC/TRAC not available during 900 miles of highway driving. The most alarming aspect is the almost complete loss of power when the fault occurs. Shutting down for a minute completely restores normal operation without a check engine light and no stored codes. There were 4 incidences during the first 450 miles with cruise control on and a single incidence during the second 450 miles with cruise control off. During short-range driving in town this fault is rare and occurs once every couple of months.
My Jaguar mechanic has spent a lot of time diagnosing this issue without finding a definitive cause, looking into the brake switch, alternator output, TB connectors etc.
I now keep my ODB reader ready to monitor codes should the fault occur again.

Could you please suggest a strategy to further diagnose this fault?

Thanks, SP

 

The most obvious cause would be a battery which is not in tip-top condition. How old is the battery?

I'm surprised that there are no fault codes. Is your reader able to read all Jaguar codes as these will not be engine codes which are more easily read.

I would also test or change the wheel speed sensors as they often don't last forever. They can be tested with a multimeter but are not expensive to replace.

Richard

 

I went through this myself, cleaned wheel sensors, etc. However turned out to be the Throttle sensor on the the right hand side of the throttle body..
Easy to change, but a pain as it uses 5 point torx, not 6 like the real world! Grr..
It was intermittant and gradually got worse, until every 3 miles !
I changed it for mid price part on Ebay and has been fine ever since

Good luck

 

Richard,
Thanks for your reply. I'll get the battery checked that is now 5 years old.
Stefan

 

Thanks for your reply. I share your concern about the sensor. The throttle body was replaced 12 years ago with a remanufactured unit.

SP

 

Hello,
I finally got the error code for the fail safe engine mode issue: P1122. The battery is in good condition. It is thus the TPS, which we suspected.
- Where can I find a good description how to replace the sensor?
- Can you suggest a reputable supplier of a DENSO TPS?
Thanks for your suggestions
SP

 

I UK, I bought a mid price one on ebay not too cheap, and looks identical tp the Denso part.. Look out for the 5 point torx to unscrew it !
Good luck

 

Note P1122 relates to the pedal position sensor rather than the TPS:

 

Thanks all for your suggestions. I am aware that the P1122 code points to the pedal position sensor. That sensor cannot be replaced and requires sensing in the throttle body for refurbishing.

I decided to replace the throttle position sensor after getting more frequent fail safe engine mode faults. The sensor from a British supplier required empirical adjustment to obtain a reasonable warm idle speed of ~550 RPM, not the same position as the old sensor. The initial test drive was fine, but will have to monitor to see whether the error reoccurs.

Thanks again

 

Dear Jaguar Enthusiasts,

To bring closure to this thread: It was indeed not a faulty throttle position sensor that caused the issue. I discovered that the clip that holds the connector to the pedal position sensor in place was broken off. I sprayed the pins inside the connector with contact cleaner and secured the connector with tie wraps. No faults so far.

Thanks

SP

 

Well found!!
You do have to wonder how the clip broke off..
Happy new year one and all

 

Old age perhaps. Some of the plastics used on the car weren't that hard wearing unfortunately, but luckily we have cable ties.

 

The throttle body was refurbished in 2012. My assumption is that the connector clip was broken off by a mechanic while servicing the car.