Re-programming the ECM

I have had to replace the ECM on my 97 XK8. The new ECM is from a car with cruise, My car doesn’t have cruise so I get a number of fault codes relating to the vacuum valves that aren’t there. Anyone know where in IDS you can change the setting in the ECM to non-cruise? I can’t find it anywhere.

Shropshire, UK

They can be reprogrammed but the only J-L member that I know of who has done the is the Ex Jaguar engineer Andy Stodart who rarely posts these days but may still be about.
I’d check the Web for UK companies that can do it.
ecu reprogramming for jaguar x300

Thanks Neil,

I do have the dealer level equipment. I just can’t find any reference to Cruise Control in the IDS programme. It must be buried in one of the sub-menus and I was wondering if anyone had already done this and could save me time looking for it.

One thing puzzling me is that I have found two write-ups of retrofitting cruise to early X100. These describe the process of fitting the vacuum system and extra wiring but neither make any reference to the telling the ECM & TCM that the vehicle now has cruise. And I don’t understand how it would work without doing this.

It’s evident that my replacement ECM ‘knew’ that the car it came from had cruise because I get three fault codes, one for each vacuum valve in the cruise system. It now checks these valves, which of course are not present, and reports a fault which shows up in fault codes and on the driver information display as Engine Fault.


This may or may not help but I used to perform ECM Flash Reprogramming when the XK was introduced. I worked at the Jaguar dealer and we did this when cars came in for service and the VIN was checked.

I think there is (was) a provision in WDS or IDS for the same software to perform this operation like PDU.

It might bring the ECM back to original configuration if all the info is corrected as to the original VIN specs.

This is for the North American market so I’m not sure this will be available to ROW or any other market??

303-35Am2 ECM Flash Reprogramming.pdf (253.0 KB)


Hi Bob,

Thank you for the suggestion. There is indeed an opportunity to re-flash the ECM within IDS but it seems only to be associated with the fitment of an updated throttle body which isn’t fitted to my car. I did think about trying this but it’s a one way process and so I decided not to do it.

When IDS first starts there is a screen where after the VIN is entered you get a list of the specification for the car. I tried putting in the VIN of the ECM donor vehicle and changing the cruise setting in that screen but the result isn’t saved. I have a feeling that the system may have to be online at that point to receive the next instruction from the JLR server or at least, that’s what would have happened when the car was current.

In fact, my diagnosis of the original problem has proved to be wrong because the fault that I thought the replacement ECM had cured has returned. This is a ‘no crank’ fault associated with the immobiliser system. It appears that from time to time the key transponder is not recognised which raises a P1260 code and the engine won’t crank. If I re-synchronise the ECM with the Body Processor and then re-programme the keys it will start again. Also if I do a hard reset it will crank once until the next start attempt.

I need to go back to basics here and re-trace my diagnosis path.