I bought a 1998 Jaguar XJ8 sedan April 20. It has 105,000 miles on it, and I knew it would need some work. Yesterday I

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Customer: I bought a 1998 Jaguar XJ8 sedan April 20. It has 105,000 miles on it, and I knew it would need some work. Yesterday I paid a mechanic $1,100 to replace all of the spark plugs and the valve cover. It was running beautifully, not misfiring like it had been for three weeks. Then today, the Fail Safe Mode amber warning light came on. I've had the car back less than 24 hours! Though it still runs great, I am wondering, did I buy a lemon?
Answered by Richard in 5 mins 13 years ago
15+ years of experience

19,890 satisfied customers

Specialities include: Automotive Mechanic, Small Engine Repairs, Auto Body Repairs, Diesel Engine Repairs

Hello and welcome to justanswer.com


The failsafe light can come on for a few reasons. It may be an electronic throttle or brake switch issue. I recommend that you go to your local autozone or parts store to have the stored codes read from the ECM as they will usually do this at no charge. Once you have the code numbers let me know what they are. Since you just had work done check to make sure that the air tube is still connected properly and the air flow meter is connected.

Thank you for responding so quickly.The mechanic that did the work I just mentioned said that four codes came up, but only the one for the misfiring cylinder (#8) was of concern. I just don't understand why the fail safe mode light would come on 18 hours after I got the engine work done!!!
It is possible that one of the other codes is the reason the light is on. See if you can get the codes for me so I can assist you with the diagnosis and repair.
Will do - thx
Your welcome. Get back to me when you can.

Hi Richard,


Here are the codes the mechanic ran last week on my XJ8 (the check engine light was on and it was running rough, especially while idling)


P0308, P0316, P111 and P1643


The complete list of work done is:


Replace 8 spark plugs

Replace 2 ignition coils ( #6 and #8 cylinders)

Replace valve cover gasket (2)

Replace park plug grommet (2)


BTW, the fail safe mode light didn't come on when I drove to the grocery store yesterday afternoon. We'll see what happens today.

Ok The P1643 is for CAN communication between the ECM and TCM. This may be the cause of the failsafe light. Now that all the codes are cleared next time the light comes on stop in your local parts store or autozone and have them run a scan. If there are any stored codes let me know what they are.
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Last Updated: 12-20-22
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