Hi Guys. After owning my XJ12 for nearly 2 years now, I've finally been able to drive it after moving back to the UK with my family. I drove it for 1000 miles this week and overall it drives like a new car. However I have a couple of issues that are puzzling.

The cruise control is difficult to engage. You can press the set button and sometimes it will engage and sometimes won't. It surges monentarily as you press it, as if you just gave it a quick press of extra accelerator. Then, it may stay at cruise for as long as you need, other times disengage by itself after just a few minutes.

The car returned 23mpg (UK) on this drive at mostly 60-65mph speeds with 2 adults, 3 kids and full luggage so I think engine and fuel wise its doing pretty well.

Last issue is a gearbox noise as the box gets to the top of 1st gear. As soon as 2nd gear engages, the noise goes away. Ive checked the box fluid level and the PO has filled it to the 'Hot' level on the dipstick when the car is cold. So, it has too much fluid in it. Could this be an issue with it? Do I need to get that extra fluid removed asap?

Cheers!

Scott

 

First gear is an easy one. First on these 4L80Es is straight cut so they whine no matter what. If you leave the switch in "N" the car will take off in second and the noise shouldn't surface. Hopefully a quick and simple fix!

 

Oh! It is in 'N' mode. Must be second then. I'll try S and see if first is noisy and second. Hadn't even tried it yet as I drive like an old lady.

 

The N / S switch makes the transmission ECU command higher RPM shift points , it also skips the 1st gear so you wont be hearing it

Your cruise control has the left rear wheel speed sensor as the speed refence , this will also be the speedometer

You may on this single speed signal be good enough for the anti - lock brakes and traction control and speedometer but not good enough for the cruise control

You can clean the face of the speed sensor different then the sensor connector

You can get to them without jacking the car with a 10 mm

Do not try too hard to remove the sensors as they break , plastic on the button plug going into the hub and expensive sensors

The wheel speed sensors are specific to ;location and VIN # as lefts don't work on rights

Your 97 is probably the later version part #s

The wheel speed sensors will read from the brake control module the same fundamental resistance of 1300 ohms

To functional test spin the wheel in the proper direction of positive car motion and the sensors will read about 1.0 volts AC

Your left rear is the pin 9 and 10 as the 2 pair marked in orange in the pic

There is a independent vacuum pump for the cruise control

The brake switch disconnect is actually 2 brake switches in one package with 1 dedicated to the brake light

 

Thanks for the detail on that. Will have a look into it.

My car is a September 94' build date. Think it sat in a showroom for a couple of years before being sold in Feb 97. The buyer traded in his 1990 XJ12 for it and got 7500GBP off the purchase price.

 

I was wrong on the wheel sensor construction as a metal cap is as goes into the hub casting and gets stuck , they break off leaving the metal cap and part of the sensor in the hub

Motorcarman had a recommendation of pushing from the inside of the hub with a long screwdriver levering

You'll have to spin the wheel just right to contact the sensor

Removing the sensor is a last step and there are a couple of things I did not mention yet

 

Let's get that transmission fluid level corrected asap! All diagnoses are invalid without correct fluid level.

Happy to hear you finally got to spend some quality time together. With the family and the car!

Also, I think your fuel mileage computer is broken.

 

Well, in Sport mode, 1st gear is noisy and so is second. Once it shifts into 3rd its super smooth and quiet. I'm booked in somewhere local for a transmission fluid change. Might as well have fresh in and have it filled to the correct level.

The mileage computer is broken! It actually overestimates! I ran it from fuel warning light on and 15mpg range (same driving conditions), filled with 10 gallons exactly and drove to 15 range again. I managed 230 miles. Dash MPG was showing 20.1mpg.