A friend and I have successfully installed the RealGuage Coolant Gauge in my ’98 XK8. However, we’re having a problem calibrating the gauge. To complete the calibration we have to be able to access the coolant temperature gauge readings while the ignition is on but the engine is off. His OBDII scanner won’t read in ignition on/engine off mode and mine gave us some odd readings (on his car and mine) when I used the Diagnostic function to get the reading from the temperature gauge.

Has anyone had a similar problem and can give us some advise?

Have you contacted Steve from the Jag Wrangler site? He is very responsive and will offer you the best advice if his products has issues.

Yes I have. Spoken to Steve twice and he is, as you say, extremely helpful. I'll know more tomorrow but there may be something that's completely unconnected with what we're trying to do that's causing the problem.