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I have a 2003 XJR that keeps giving me a failsafe, limp mode and P1631 code. Usually happens after 40+ miles of driving, happens quicker and more frequently in warmer weather, almost immediately on hotter days.
Clearing codes with a handheld and waiting 30s-1 min allows you to drive again, sometimes for a few minutes, sometimes a few feet.
Worst instance it would crank, stumble
and stall. 90+ degree day, car in the sun. Had to remove the ecu and put in AC. Plugged back in and
made it 15-20 miles before it went out again.
Suspected a short in the ecu that flares up with heat but board looks perfect. Any ideas?
P1631 relates to a faulty throttle control relay, located in the ECM box under the hood, looks to be the 3rd along from the outside of the car. A dying relay would go faulty with heat - more doubtful is the ECM.
Switch the relay out for a new one.
Hope this helps.
Forgot to add - that’s what I found when googling the code - not a lot of posts about it - I swapped relays twice to make sure it didn’t change. Definitely heat related - thinking g a failing ecu box fan may be the root cause...
Update - the small pc style fan that blows air out of the ecu box didn’t seem to be moving much air. I wired a larger pc fan in and it’s pushing a LOT more air out. Made it home yesterday with no failsafe or faults - fingers crossed!
Its probably not going to be a direct answer, you'll have to research it some more. Try this (bookmark it also)... JagRepair.com - Jaguar Repair Information Resource ...you can do a search of the electrical diagram, download and review as you determine any faults. I wouldn't stop if you find a fault, be sure to trace it out for more or you'll be cussing yourself thinking you fixed the wrong thing when it could be multiple things.
P1631 code, failsafe limp mode
