I have never seen an issue like this. I got in my car Friday afternoon after work, started it up and the temp gauge warning indicator (red) was on and the gauge stayed at zero. Everything else worked. I plugged in my OBD2 and the PCM indicated the correct coolant temp.

Drove home, restarted, same thing. In this photo the PCM indicated the coolant was at 197F.




The owner's manual and the FSM say nothing about the "overtemp warning light" being on with no gauge reading. I tried to get into Engineering Test Mode to verify the gauge could still sweep, but I'm not able to get in. Holding the trip button while turning the key from 0 to II, nothing happens. I've been in Eng. Mode before, not sure why it isn't working now.

What in the world... this is the kind of problem that makes me want to get rid of this car. I'm going to get out SDD and see what codes are stored, then also try cycling the battery.

Anyone ever seen this before?

 

See below re car data

 

It's an 06 XJ8-L

 

First ting to do is read the codes. Write them down but a lot of them may have nothing to do with the issue.

Next is to look at causes for the codes, id also clear the codes and check the IC again as this may resolve it.

I doubt its a sensor issue as you can read the actual coolant temp. this is not the temp gauge reading as it faked into an idiot gauge (by the IC I think)

Always possible you have an IC issue and if you do id try a reflash before sending it for repair.

It may also be a bus issue where the IC is not getting the data but id expect it more issues to be present on the IC if that was the case

Let us know what you find. Id be interested in the codes you get

Oh yeah forgot, check you battery as well, long shot but check anyway

Cheers
34by151

 

This might help:

Go LPG - Common X350 faults

 

Thanks 34... the car sat overnight before I had time to get out SDD and take a look. And of course, not too much of a surprise, but everything was fine when I turned the key on.

I did pull some relevant codes. U2199 - missing temp data, and more importantly P0116 (history) is "ECT circuit range/performance problem." I saved the freeze frame data for that one. I may have an intermittent bad connection to my ECT after all. That would explain the random rich condition fault code as well. The list of codes is not long because I had cleared out all the history codes about 6 months ago. It had accumulated all kinds of random crap over the years. Also, the battery is only a few years old (from the dealer).

But, the good news is that everything is working fine again. I will keep an eye on it and take a look over the coolant sensor circuit.

I'm still baffled why Engineering mode doesn't work on my IP anymore. I have been in that mode before, now I can't get into it. I'm holding "trip" while turning the key from 0 to II, but nothing happens.

 

Ive never tried the IC engineering mode, I just use SDD
Oh yeah after thinking about it I realized I rarely look at the temp gauge

I have Torque that comes up with the Ign. On that screen I have the fuel trims, Temp, Boost, and O2 sensors

It is also setup with High and low alarm triggers. These are set to trigger when outside normal range.

The upshot is I look at this more than the IC and really only look at the speedo

Cheers
34by151