I've had some issues with mine on the XJ...sensor, and the lead.
Fix: replace sensor in instance one. Ran for another 18 months before...
Fix 2: heat shielding had been pulled back from the lead....
Symptoms: when mine has been sensor related, and lead, with malfunction or shorting, I was reading HIGH pressure with needle well over the high mark, and was always erratic (bouncing from 12 o'clock to 3). I have yet to see it read LOW with either of the above problems. It might just be mine, but...doesn't seem characteristic.
Oil 10W30 dino, or synth?