Various electrical issues- advice please!
 

Hello,

Bought an XK8 (2000) in April and had her in the garage after 2 weeks when it went into failsafe mode. Garage said it could be O2 sensors (as did AA man) or possibly the whole computer module up the shoot. They also found a transmission oil leak (which they repaired, but is fairly irrelevent to this post).

Since then it's been to independent Jag specialists who replaced O2 sensors. 1 week later failsafe mode again. This time Throttle Body sensors, which the garage cleaned up. 1 week later, failsafe mode again...

The problems seem fairly intermittent. It's taken out on test runs and put back on diagnostics and no codes come up, but then a week or so later they'll return again.

I have 3 main issues- the throttle body sensors and/or circuits are most frequent, plus ABS light (including trac unavailable) infrequently comes on, and I've also noticed that the airbag light on the passenger side dashboard stays lit for up to 5 mins occasionally before eventually going out.

I've spent hours reading posts on here as a non-member and there's some brilliant stuff and advice which I could use.

But my question is this: Should I spend a lot of time and money repairing things, e.g. replacing the throttle body, cleaning speed sensors, refurbishing ABS module etc. OR is it more likely to be the computer module sending out false messages? In which case from what I gather, replacing that would cost a couple of grand and probably not worth it.

Hit me with your wisdom.

Thanks!

If you have not brought a battery yet and the one in there is of a unknown date, your first move is to get one and check out the charging system in any case.

Wayne

+1 On checking the battery first.

The cats are notorious for sending out random codes when the charge is low. Yours shows classic signs of a weak battery.

+1 for whatever reason low voltage is not a good thing.

Worth getting the current one load tested first or just buy a new one?

I gather it's around £120 for a new one?

Sorry, I can't guess on the price as the last time I was in Canterbury was 1962 on honeymoon.
Good luck and that price is about what we pay here. I always look for a email from the parts stores, they are always offering 15 to 20 % off.

Wayne

Euro Car Parts have a summer sale on, £75 :icon_dance-twist:

Thanks, just been to Eurocarparts to get a new one and replaced that. Will see if it makes a difference.

Planning on cleaning the speed sensors too but at the moment I can't get the big nut off to expose the wheel nuts... Gonna have to borrow Dad's massive adjustable spanner I think. Doesn't seem possible to be able to change a wheel at the side of the road...

Unless of course you guys know something I don't.

If the new battery doesn't cure the faults was the engine pressure washed prior to your purchase? Mine was when I bought it - spent three weeks chasing random codes - eventually I removed and cleaned every connector I could access - it doesn't take much moisture in them to confuse the electronics. I also zip clipped the TB connectors to make sure they couldn't move - there's also a TSB about incompatible pins on the TB connector - not sure if it applies to your car - it did to mine (99year)

can get at the speed sensors to clean without removing the tires . the fronts are easier if you turn the wheels side to side. theyre held on by one bolt if i remember correctly . i used very fine sandpaper till i could see the metal again.

Not sure what you mean about the wheel nuts but .............. with the jack and wheel-brace in the boot, there should be a sort-of plastic tube. This pushes over the wheel nut covers, and then you pull the cover off with the tube. You then push the cover through the tube to get it out again.
Once the "proper" wheel nut is exposed, the wrench in the boot should get them off.
Make sense ?
Cheers,
David.

I've had similar problems. A new battery, and O2 sensors cured a lot of woes. Most recently, hit a bump in the road (the last one was a speed bump while going 3 mph), and ABS, Trac Off, and fail-safe would immediately ensue. I was amazed that cleaning the wheel speed sensors seems to have rectified the problem. It's been 3 weeks now and there has not been a recurrence.

The front sensors face the front of the car. Turn the wheels, and you can see the sensor held in by a single bolt. The rear sensors are on the top of the axle. I can't think of a way to get at them without removing the wheels.

There is a video of removing and cleaning the sensors by Reverend Sam among the tech service sections this area of the forum.

OR is it more likely to be the computer module sending out false messages? In which case from what I gather, replacing that would cost a couple of grand and probably not worth it.

Hit me with your wisdom.


On my 1998 XK8, I frequently get the message, with an amber warning light, Failsafe Engine Mode. This is supposed to be accompanied by a loss of power but such is not the case - it continues to run fine and perform as expected. However, my cruise control ceases to operate, so it is possible that I have a faulty/intermittent brake light switch. My brake lights work fine, so all I am losing is use of the cruise control until I shut down and give it a rest. Next time I set the cruise control it usually works OK as long as it is not reset a few times. I got used to a computer sending me silly messages with my 1999 BMW 328i convertible which preceded the Jag - low coolant level and non-working brake light circuit, both of which were untrue, so I don't get too upset about the "Failsafe Engine Mode" message from the Jag as long as I still have all the power.

After you fit the battery check the charging, you should have approx. 14 to 15 volts at the battery terminals with the engine running. Poor or no charging will knacker the battery in no time.

Get down to Maplin and buy yourself some electrical contact cleaner, use this with a stiff plastic brush to clean the ABS sensor faces. Then disconnect the 2pin connector and give the insides a good squirt - any green deposits are corrosion and should be cleaned off before proceeding any further. Next check the wires themselves and make sure they are not broken or the insulation's wearing off.
Use a small wire brush and some engine-cleaner fluid to clean the toothed reluctor wheel on the hub; corrosion and crud here cause no end of problems. If any of the teeth are missing the ABS circuit will never work - replacement is the only cure.

I've had the pins changed to the gold ones, with no success.

I'm not aware of the engine being pressure washed, but then again I wasn't aware of many little things since buying the car... Let's say I certainly won't be using that dealer again in a hurry.

Unfortunately mine's been going into full failsafe mode with loss of power. Except when it's the ABS light which just loses traction and ASC but no power loss so still drivable.

Sharay- I've been under the car and can see the front ones, which do look caked in dirt. But I've also had the added issue of no locking nut key with the car. So getting the locking nuts taken off and replaced with regular ones. I know this isn't essential for the front sensors but means I'd be able to change a tyre on the side of the road, which I wouldn't be able to with the locking nuts.

Multiplecats- Thanks for the advice, will do those tomorrow once the nuts are sorted. New battery has almost a whole extra volt than old battery at rest but not yet tested charging.

OK that shows your previous battery probably had one cell (1.2 volts) short-cicuited - ie duff :icon_wink:

Thatch - Mine was going into full fail-safe too. Hit a bump &, ASC not available, Trac off, fail-safe with loss of power, and check engine light would result. The first couple times, I'd pull over, turn it off for a few minutes, and it would run properly upon restart. Then, for several days, it would be in fail-safe upon start . OBD codes pointed to throttle position sensor and mass air flow sensor. That's when I found Rev. Sam's video on the the speed sensors. I was totally amazed that removing and cleaning them with soap an water resolved ALL of the issues. After driving a couple days, the check engine light went out on its own, without having to be reset.

I hope you get the locking lugs off soon. I did a test drive after cleaning only one rear sensor, and it appeared the problem had already been solved, but I cleaned the other 3 sensors just to be sure. Besides, you'll want the ability to change a flat, it's rather important.

https://www.jaguarforums.com/forum/x...ed+sensors+xk8 shows location of the sensors you can feel the rear ones and remove and clean also without removing the rear wheels.

an idea on removing the locking lugnuts then buy 4 replacement reg lug nuts. they're using a socket that fits snug when first started but wont go all the way down then hammer it on. will ruin the socket for any thing but this but cheaper than paying someone you tube has some other videos also but they're basically the same.