Took the XJR on another road trip this summer.

Tripped over something that has happened before and wonder if it's common, or just this one.

After a run across the California desert (LV previously, and Needles, this year), we stop to fill the car and stretch. It's over 110 F ambient and sits for 15-20 minutes. When restarting, there's a check engine light, but I cannot find anything wrong (there's oil, coolant's good, ...). Once set, it persists all day, through various stops, but usually resets overnight.

The second issue is with the air suspension. This trip had a variety of altitudes (sea level at home, 6000+ feet in Arizona, 13500 in Colorado on US 50, 9000+ in Wyoming, ...). The air suspension would fault at about the time that it should lower the car (50 MPH, IIRC). Again, it would stay faulted during multiple restarts, but otherwise it all seemed to be working OK. It did reset on a restart at lower altitude.

I haven't had a chance to get a dealer to pull the codes. Next month when it hits 80,000 miles, probably.

Thoughts?

 

I'd suspect neither are actual issues.
The CEL: at that heat and with a fillup, a lot of vapor would have to purge itself from the tank, lessening the vacuum seal and causing the light..... when there's a seal issue it can take a while for the light to go off.

The air suspension: well, going across those kinds of altitude changes is gonna cause ride height changes with no input from the car due to the lessening of exterior pressure. I can see that causing a fault light.
As a side note, the car shouldn't lower itself until 94mph I believe.

Sorry for the less than technical explanations. ...it's late on a saturday....

I'd be very wary of the shop trying to sell you any 'fix' for these 'problems'

 

Excess heat is not usualy a problem here!

Did you idle the engine for a few minutes after stopping, to let it cool down?

A trick my old dad learned when serving in North Africa was to turn on the heater for a while to drain more heat out of the coolant. You would want to be stopped with the windows open...
If the a/c is still on it will be dumping more heat into the engine bay

the SC engines (at least) have an auxiliary coolant electric pump hidden behind the front RHS bumper, you may hear it whirring after you turn off the engine when very hot.