The brightness of the instrument cluster seems to regularly go dim in my 2002 XJ, with a P1238 error code suggesting instrument cluster is over temperature and dims the backlighting to help control the temperature - but this happens on warm and cool days.

I looked up live data and see the instrument cluster temperature moving around like crazy, so I assume a faulty sensor. Anyone dealt with this before?

I guess I'll remove the dash and see whether there's anything to be seen... but I'd assume a temperature sensor is unlikely to be a replaceable item.

 

With a bit of soldering I'm sure the thermistor could be replaced. Or maybe even it's just a cold solder joint at the base of the thermistor causing bad readings, might be able to get away with just reflowing those joints with a bit of flux and calling it a day

 

I certainly hope so. I can’t find a schematic showing where the thermistor is situated yet. Would it be in the panel somewhere, or a module controlling backlighting perhaps?

 

When I worked at the dealer a few decades ago, we got TECH TIPS for a few years.
I saved all that were sent and there was one describing your concern.

 

That describes correct function at high temperature - but in my car it randomly changes at all temperatures, hot or cold. It can flick bright/dim several times on a drive - and when looking at live data it is all over the place, which is what’s leading me to assume a faulty sensor triggering the action which would be correct at high ambient temperature.

 

The INSTPK for the AJ27 X308 is NOT configured to the car BUT it would be wise to get the VCATS and try to match.

PLUG&PLAY for the IC but the mileage will be what it was in a 'donor-car'.

You could also try to disassemble and make two-into-one? from a salvage part.

 

Thank you, that’s good to know!

 

There's two on the front-facing side of the instpk main pcb (at least on the donor board I have), they're hard to see in the photo but very easy to spot in person as they stick up from the PCB - and they're labeled "therm1" etc.

 

Nilanium, I can't begin to tell you how grateful I am, that saves me an awful lot of guesswork. I can now remove the cluster with confidence, check the part numbers of those thermistors and order replacements.

This forum is full of good people - glad to be part of such a group.

Thank you,
Jeremy

 

Interesting and just a side note?
I have a late model XJ (X351) and in that car Jaguar ran cooling ducts to the backside of the drivers IP and the center navigation stack inside the dash board. So it looks like a fix/upgrade for an earlier known problem.

I only got into this because people (Including me!) have replaced the navigation screen with a larger after market Android tablet. Some units you had to swap the OEM boards over to the tablet. This kept the panel cooling working as designed. Others have just stuck a tablet in and many suffer heat failures because of no cooling.

I had never heard of such a thing before and here over 20 years ago Jaguar was already monitoring it!
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