Gearbox/DSC/ABS faults

[PaulGover]

Recently I went shopping after a long COVID-19 gap, so the car's battery was nearly flat - though it did start. Then at traffic lights I decided to put the car into Park rather than Neutral (not sure why I did that, something to do with rust in the cranium ), and moved the gear stick rather fast. And as I drove off, I got a load of instrument panel warnings cycling through Gearbox, ABS and DSC faults, with the gearbox going into limp-home mode.

I have a Foxwell diagnostic box, so I plugged it in and found the following codes:
C003A-07/1 rear RH speed sensor signal out of range;
P0720 output speed sensor malfunction;
P0730 Incorrect gear ratio;
P0735 5th gear ratio incorrect (too little Tiff Needell?);
P0701 combination of something (I can't read my writing, but the gearbox is implausible); and
also errors concerning the steering wheel position sensor and the yaw detector.
(I see similar reports on the forums, but not with all these symptom codes listed, so I put them here for completeness.)

Digging about online it all results from the failed RH speed sensor. It appears the gearbox relies on its signal to work out how fast the output shaft is turning and together with the other sensors whether the car is turning. Since the signal had gone, it seems to decide the RH wheel is stopped, so (a) the car is turning right despite the steering wheel and yaw sensors saying it's going straight on, and (b) the back axle is turning too slowly so the gears have stripped all their teeth or the clutches are slipping. You'd have thought I might have realized it was the sensor that was duff rather than the steering and yaw and gearbox all failing simultaneously. Whatever ...

I bought a new sensor (£50); dead easy to replace - remove the rear wheel, undo one screw, unplug old sensor. It appears to have cured the problem.

The only bit I don't understand is why moving to Park too quickly seemed to trigger the problem. There were slight symptoms before - a occasional lumpy gear change, but no warning lights.

[BrianG]

Hi Paul,
It seems these wheel sensors can just fail whenever they feel like it. A few months ago I parked a perfectly running car for a hospital appointment. When I came out, started up and as I put the car in reverse and moved a couple of feet the dashboard lit up. Restarting the car, which sometimes clears gremlins, made no difference. I had ABS, DSC, TRAC fail lights on and 'Cruise control not available' on the message panel.

Back home with the iCarsoft 930 it pinpointed the left rear wheel sensor which had no output. Annoyingly you can't easily test them: there's no "continuity check" you can do as they are hall-effect devices. I bought a new one from SNG Barratt - not the genuine Jaguar one but like you a £50 UK made one that they do. I was a bit concerned that the new one also did not pass any sort of continuity or diode check with my digital meter, exactly the same as the suspect one, but I fitted it and hoped for the best. All was fine once I had driven the car and cleared all the error messages.

There are ways to check these hall-effect sensors but not easily at the car. It requires a separate power supply, magnets, and an LED in series with the device. At £50 it's probably easier the trust the diagnostic device and whack a new one on and see what happens!

[jeff1954]

Hi Paul glad you've solved your problem, But why would you want to take it out of drive at the traffic lights in the first place.

Jeff