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Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 22932
Experience:  BEng hons Mech engineering, in auto industry 22 years
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i have a 2001 jaguar xjr and has just started intermittently

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i have a 2001 jaguar xjr and has just started intermittently going into limp home mode with a warning of asc fault the engine revs rise on tick over and a single gear is selected and no throttle response i pull over put the car in park turn off the engine and wait a few minuates restart the engine and it runs fine untill it does it the next time


This sounds like an electrical actuator or sensor at fault .Usually when you can cycle the ignition key on / off and then restart the engine and the fault is gone temporarily this indicates that this is an electrical component causing this issue.

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Also replace the spark plugs if any of them fail this checklist:

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

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Customer: replied 3 years ago.
Hi Matt,thanks I know where some sensors are located , but do not know location of O2 , crank , cam ,, or throttle , can you help. Regards martin
Hello Martin

the O2 sensors are in the exhaust pipe just before the large bulge of the catylst
the crank sensor is on the back of the engine and points at the flywheel
the cam sensors are on each cylinder head at the front of the engine

and the throttle sensor is built into the throttle body / butterfly