It's Electrical Gremlins Week! OBD reader saves the day

[BrianG]

Hi folks,
Sorry if this is rather rambling but I've just had the most annoying few days with my 2006MY X350 3.5 V8 which may be of interest to other owners. Last Friday afternoon I went out and the car was running fine, no problems when I parked. When I restarted about half an hour later, on moving off I got the lovely string of messages on the instrument panel screen "DSC fault, ABS fault, Brake Booster Fault, Cruise not available" and the amber light. Cycling the ignition made no difference so I drove home carefully and on Saturday morning got the trusty iCarSoft 930 out and this diagnosed code C0037- rear left wheel sensor fault, but no other fault codes. Just in case it was a battery-sensitive problem I charged the battery overnight in the car, and tried again on Sunday, but the fault codes came back after being reset.

I took the wheel off and unbolted the sensor to check it. Because these are Hall-effect devices these are not readily testable with a multimeter continuity test, so as the sensor looked a bit rough physically I took a chance and ordered a new one from SNG Barratt. I considered checking the continuity of the wiring from the rear wheel as suggested in the workshop manual, but this is almost impossible single handed. As the ABS pump and its connector are right at the front of the engine bay and were covered in crud, I checked inside the connector for possible bad connections, but this was OK. I figured that any suspect wiring breaks at the rear wheel caused by suspension movement would most likely produce an intermittent fault, whereas this fault had now been solid over a few days.

SNG Barratt do a cheaper sensor at less than half the price of a Jaguar branded one, so while waiting for this to arrive in the following week the car now decided to announce its displeasure by throwing a wobbly with the front parking sensors going berserk at random when no object was near enough to trigger them. I stopped this with the switch on the overhead console but the following day the problem was replaced by the "Check Engine" warning light coming on solidly but the car running perfectly.

The new sensor arrived and I checked it with my multimeter just to see if it was any different to the suspect one. No! effectively open circuit with the meter probes either way round, the same as the suspect one. Oh damn! Today with the break in the weather with fingers crossed I fitted the new wheel sensor anyway, cleared the codes and started the engine. Now I got the joy of a new fault: the red "High temperature" warning light on permanently and the temp gauge itself inoperative. This could not be cleared by the iCarSoft and kept coming back. Clearly this was wrong as the car was stone cold, so I ignored it and went off round the block to check the new sensor. Hooray! No DSC, ABS or Brake booster faults and the iCarSoft 930 happily showing live data from that rear wheel. 'Just' the Cruise Control Fault and the temperature gauge to sort out. The idle was a bit high and the engine running lumpy, but clearing several codes in the Engine display group screen sorted the idle, the temperature warning light and made the temperature gauge operate. I then had to go through every screen and clear a host of fault codes that were not there before. Finally got all fault lights extinguished and the cruise control working again.

It seems one simple failure can throw up a whole load of other unrelated problems on these cars. I bought the iCarSoft 930 about two years ago; it could not correctly diagnose a problem with the reverse parking sensors last year (faulty module) but this time it's now proven its worth without going to a main dealer to sort things out!

[J44EAG]

As we know, Brian, electrical gremlins can come out to play for no real related reason(s). Winter weather conditions seem to exacerbate faulting.

I`d offer the following advice on the apparent engine temperature issues. I`ve seen a full hot gauge but cold engine almost refuse to let the engine start. I had this on the V8 S-type and also on my current 350R......both at around 80K miles. Changing the coolant temperature sensor immediately fixed the faulting in both cases. 80K on those sensors appears to be about the maximum reliable limit. Before they fail completely, you can also find lumpy running a feature of impending breakdown. Best advice from my own experience is to totally avoid after market copies of the part which I`ve found to make issues even worse. Use genuine parts only on Jaguar electrical systems.....but you know that already!

A genuine temp sensor is around £23. As an aside, thermostats also play up at similar mileages. Replacement makes a huge difference to the running qualities of the car. Well worth changing the two parts at the same time. Ensure you pick the correct thermostat parts. There are about six X350 stat part numbers listed!

Mike