Missing a height sensor

1680 Views 7 Replies 3 Participants Last post by TonyXJR, Jun 3, 2012

Cambo351

Discussion Starter · Jun 3, 2012

I was poking around under the XJR this evening, doing my homework before attempting to lower the car by shimming the height sensors, when I came across a problem.

There is a sensor under the right rear, left rear and left front, but there is no sensor under the right front.

It's simply not there, and by the looks of things, it was never there to begin with...

I'm not kidding, there should be a height sensor there, you can see the notches in the rear lower arm where it would be strapped on, and there are rusted out holes on the subframe where the sensor should be bracketed on.

There are no loose wires visible anywhere. I'm kind of shocked at this....

Begs the question; how can the air suspension be working like this? did someone tap the left front sensor to both front inputs of the ASM? did it leave the factory like this? why wouldn't any of the four different dealers who serviced it in the past notice?

Is it even safe to be driving it ? Bloody hell i hit 150mph on the Autobahn yesterday...

Help! What do I do now?

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TonyXJR

· #2 · Jun 3, 2012

The fourth sensor was deleted in all cars built after December 2003.

I think Jaguar realised pretty quickly that four sensors were unnecessary, and probably caused more problems with mismatched readings (it may cause the system to hunt, without a big slug of hysteresis).

If you think about it, you would be unable to vary the height of one wheel without affecting the opposite wheels sensor.

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djdex

· #3 · Jun 3, 2012

Don't panic Cambo, the early cars had 4 sensors, this was later changed to two rear and one front sensor, I'd say your car is fine.

Doh! Tony beat me to it!

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Cambo351

Discussion Starter · #4 · Jun 3, 2012

Thanks guys!

Well that was an embarrasing overreaction. Had me going since the JTIS clearly shows four sensors...

So now I wonder, will shimming the left front sensor lower the front evenly?

I measured the front (not scientifically, just with a tape measure)

After 3 hours stationary; RF 390mm, LF 395mm
After starting the engine; RF 394mm, LF 396mm

So maybe I have a slight leak in the right front?

In any case, the drive height seems even enough, i'll let everyone know what comes from a 5mm shim, which should lower the front approx. 1"
Rears i'm looking to shim around 3mm, to lower around a 1/2"

Still doesn't make sense to me, if they wanted to get rid of one sensor, then why not take one from the rear, most all air suspension setups (Benz, for example) use two sensors at the front and one at the rear..

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djdex

· #5 · Jun 3, 2012

I look forward to your tutorial on shimming these sensors

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TonyXJR

· #6 · Jun 3, 2012

Cambo351 said:
Still doesn't make sense to me, if they wanted to get rid of one sensor, then why not take one from the rear, most all air suspension setups (Benz, for example) use two sensors at the front and one at the rear..

Maybe with the XJ they felt rear passenger comfort was more important?

The latest XJ only has air suspension at the rear, with conventional springs up front.

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Cambo351

Discussion Starter · #7 · Jun 3, 2012

djdex said:
I look forward to your tutorial on shimming these sensors

I'll even throw in a set of steak knives!

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TonyXJR

· #8 · Jun 3, 2012

When I was playing around with the Autologic Diagnostics unit (http://www.autologic-diagnostics.com/media/uploads/pdfs/brochures/Product_brochure_EN04w.pdf), it looked like it would let you program the ride height.

IIRC, mine was set to "15".

I didn't try changing it, as I've got enough things to fix on it without creating more.

I might take a man-pill though & try it anyway

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