I have a 2004 XJ6 which has been a totally reliable car for 12 year until recently when the car would not start. Turned the ignition key and absolutely nothing happened and steering column remained in locked position which made recovery something of a challenge!. Car returned to Jaguar dealership on a low-loader but the dealership could not determine the fault as they cleared all codes in setting up diagnostics which effectively removed the glitch whereupon the car started and did so reliably until exactly the same thing happened again three weeks later. Once again the dealership did exactly what they did before and once again were unable to identify the problem?? I spoke with Jaguar technical services who were unable to give any indication of where the fault lies and said that they would be unable to do so unless and until the problem replicates itself during diagnostic testing - in short they were less than helpful! So much for modern technology as I now don't know whether next time I get into the car it's going to start or whether I am going to be booking yet another call to Green Flag - very unnerving!

hi

do you know what fault codes were reset, might point you in the right direction

also if the xj is anything like a s-type, if the battery gets low, it can throw up many faults and codes

they might of charged the battery, cleared the fault codes and hey presto its ok ( till 3 weeks later )

I'd be tempted check the battery, it should be over 14 volts when running and never below 12 volts when not running.

battery is a common problem on s-types, if you have over 14 volts when running, could be just battery.

cheers

Joe

Hi Joe

Thanks for the reply. I don't know which fault codes were reset by the diagnostics whizz at the Jaguar dealership but he did say that the fault might be in one of several places which suggests that there were a number of fault codes recorded? Following the first occasion the car had the battery lead replaced and a barnd new battery fitted so on the second occasion of non-starting this should not have been down to a low battery?

I will ask the dealership to double check the battery and voltage so thanks for the tip!

 

Regards

Roger

hi ,roger. on reading your problems its seams that the main dealership have not found the route of the cause to this issue? but performed a hard reset or maybe reprogramming, because after 3 weeks you say its back to normal. so when diagnosing an electrical fault, assume that no defect exits in the relatively (cm) control module. maybe a defect is more likely in connectors or switches initial diagnosis should concentrate on these components. as inputs and outputs can be monitored via diagnostic equipment, if these are proven to have no fault the failure may lie with the control unit.  just a thought for you to think about!   good luck, 

Hi David

Many thanks for your post. I believe that the dealership did a hard reset on both occasions that this fault presented itself but since having performed the reset on this second occasion of the fault arising they have kept the car to see whether the fault would repeat itself whilst they were running diagnostics on it but of course it hasn't!! Electrics/electronics is not my strong suit so I have to trust that they have carried out all necessary tests and checks which i would hope included connectors and switches to which you refer? To be honest, I am still at a total loss to understand why the fault code that must evidently have been given off when the car failed to start was not immediately readable when the dealership connected it up to their diagnostic computer? When you say control unit please enlighten me as to how this unit differs from the control module, for as I understand it, their are a number of electronic modules, each performing a different function but each interacting with one or more of the other modules?

sorry roger for the confusion of the word" unit" should say module. i do hope that they do a road test as the problem may show itself when driven? even so it seems that they are slowly getting to the root of the problem! just a matter of time. good luck on this and i look forward to the final outcome of what the cause turns out to be? 

David, thanks for the clarification. Yes, they did do a road test but the car has behaved normally throughout the two weeks or more during which they have had the car.