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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21721
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Jaguar XJ81: 1998 XJ8 running well but "restricted performance&qu

Customer Question

1998 XJ8 running well but "restricted performance" warning. What should I do?
Submitted: 2 years ago.
Category: UK Car
Expert:  Matt replied 2 years ago.
Hello On any car if you get a check engine light or other fault message this typically means one or more of the sensors has failed or has a faulty connection. The fault can be something quite simple and nothing that’s going to stop the car to something quite major that will reduce engine power and possibly stop the engine The ECU senses this and may put the car into 'limp home' mode which typically limits the revsand the amount of power available. Usually the car is safe to drive for a short distance as the mode isintended is intended to get you home without incurring any engine damage The quickest routeto repair is to have the car plugged into a diagnostic machine which will readoff the fault code stored in the ECU (providing the light is still on at thispoint) and indicate which sensor has failed or whether the fault is more serious. You can do a very rough and ready check yourself by unplugging sensors one at a time and seeingif any of them change the driving condition which would indicate the most recently unplugged sensor is the faulty one. This method is not foolproof though and reading a fault code off is the better method. if the car is hesitating on acceleration then it could possibly be an air leak or other fuel system problem
Customer: replied 2 years ago.
The restricted performance disappeared of its own accord. Why is that?
Expert:  Matt replied 2 years ago.
I'd suspect that you have a failing sensor or poor electrical connection as an intermittent electrical fault will react exactly like this
I'd suggest getting the car fault codes read when you can to try and get a head start on when this happens again

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