Hi everyone,

This is my first post - I know it's a topic that's been raised before, I've searched and read those threads, but they don't appear to match my problem specifically, so I'm hoping someone can help me out.

I've got a 2007 Jaguar XKR with about 80000 miles on it. The car has been sat for about four weeks with very infrequent runs of short distances during that time. I took it out for a long run on Tuesday PM, and after about 20 minutes of driving hit the motorway. I stuck cruise control on and settled in. After a further five minutes, the car started to slow down/speed up in waves, sort of like it was hunting for fuel. I took cruise off, which sorted the surging, but the speedo started fluctutating by about +- 5 miles per hour in a regular up/down. Then an ABS fault popped up on the dash. I got to where I was going, and on the way home the ABS error popped up again, followed by a CATS system fault (and DSC not available). I also noticed that the speedo was slow to catch up to reality - i.e. on accelerating from a standstill the speedo would read 20 mph for 10 seconds or so, then suddenly shoot up to 50/60/whatever. Driving round with an ABS fault isn't the end of the world, but the car's damned uncomfortable to drive with CATS not working.

I did some research on this forum and others, and it appeared that a dodgy battery might be the cause. This fitted the symptoms - dodgy battery causes random faults in the electrical systems - such as registering ABS issues and CATS issues where no issues exist, and the intermittent speedo oddness. I also put the surging in cruise down to the car reading the unreliable speedo.

Here's what I did.

1. Plugged the battery into a battery charger for 24 hours.
2. Checked the voltage output of the freshly-charged battery (13.x volts)
3. Turned the car on, checked voltage again (14.x volts)
4. Took the car for a spin - still showing ABS and CATS errors.
5. Touched the -ve battery lead to the +ve lead for a few seconds, and then disconnected the battery leads for ~24 hours to try and clear the errors in the ECU
6. Charged the battery for ~24 hours
7. Turned the car on - still showing ABS errors. I didn't take the car out this time, but I assume as soon as I started moving the CATS error would show up again.

So my questions are:
The battery is most likely original to the car so is definitely aged, but do those voltage readings suggest that it is ready for replacing?
Are the ABS and CATS faults genuine, or are they a residual symptom of the previously low battery?
How do I go about clearing those faults from the ECU? Do they need to be "cleared" or will they go away as I drive the car and the sensors catch-up with reality?

Thanks in advance guys - this is the first problem we've had with the car in ~12 months ownership so I'd like to get it sorted.

 

Welcome to the club. First and foremost, with persistent problems once the battery has been verified, pull the codes and see if there's a common tie between them. Everything in your description points back to how the processors interpret the speed reference. I had one wheel speed sensor come loose on the back and it gave the same faults. The codes for the Instrument cluster, ECU and ABS modules pointed at it.

 

Thanks for the reply.

Do I need a specific (i.e. Jag-dealer) code reader? Or will my bluetooth OBDII reader get the codes I need?

 

I have an iCarsoft LRII. It will read the individual module codes. A local shop should be able to help you out for minimal cost. In the US code reading is free from most chain auto parts stores.

 

Seriously, if that is an original battery in a 2007 vehicle, and you can verify that from the battery codes, replace it NOW before you go any further. Don't think or discuss further - just do it.

 

Wheel speed sensor, find out which one and replace it. $60 part

 

Update: Another long drive on Sunday.

ABS fault still present, CATS fault no longer there. CEL turned on about halfway through as well.

Also got my code reader on there:
C0037 - LEFT REAR WHEEL SPEED SENSOR
P0500 - VEHICLE SPEEDS ENSOR CIRCUIT MALFUNCTION.
No other codes, so I assume CATS is fine, and CEL will clear with ABS?

I'm going to remove the rear left sensor and clean it, but obviously it may need replacing. No biggie, but:

1. Am I better off replacing both rears at the same time (i.e. now one has gone, is the other likely to go too?)
2. Has anyone got the part number so I can hunt one down?

Cheers,

Sam

 

Before wasting money, pull them both and swap them side to side. Then drive it and see if the fault follows the part or if you have another underlying problem. I think it was just an 8mm wrench needed to pop them out and they are easy to get to from behind the tire.

 

Well cleaning it didn't work, and the bolt was damn near welded in, so I need to replace that as well now...

Good thinking. I'll try that tomorrow.

 

Update:

Swapped the sensors at the rear, and the fault followed the sensor, so I've ordered a new one of those, delivery by Saturday so I'm told.

I also searched my bolt box for a pair of bolts that match the threads of the now-ruined bolts, and found a couple, so I can replace those too.

Many thanks to everyone for the advice - I'll update once the new sensor is fitted.