So I left work today and when I started the engine, it quit immediately, but it restarted with no problem and kept running with no issues. Not the first time it's quit on starting, which I attributed to it being cold out, but it always restarts with no problem. I mention it only because it could be related to what follows? Then when I had driven maybe a half mile, the check engine light came on for maybe 20 seconds, then went out again. Checked and found a P1495 code (Leak Detection Pump Solenoid Circult) when I got home, CEL is still not on. This is a 2000 XJ/4.0/auto.

Now I've looked up and understand, more or less, what the code is, but what I'm unclear on is why it would light the CEL for only a brief time and then go out again? I thought it took at least one drive cycle to clear it?

The only other anomaly is the oil pressure sensor (just over a week old) just failed again, showing zero pressure, on the same drive. Also I just filled the gas tank yesterday afternoon, so could be a leaky gas cap? Removed and replaced it, just to be safe, I guess I'll see what tomorrow brings.

Of course this comes up when my emissions test is due, and a string of bad weather coming...

 

If the gas cap was original that was probably your problem. The error code was probably pending and then reset. Each code usually has a different set of parameters necessary to reset/clear it. For example a misfire code might only need a 2-3 drive cycles to clear, whereas an evap leak might take longer.

For reference, the LDP is in the passenger side corner of the engine bay by the firewall:

 

I'm guessing the gas cap is original, it looks pretty old. I'll get a new one today; I have to go to the dealer to get a new oil pressure sender anyway. This morning driving to and from work (5 miles each way) the light kept going on and off intermittently.

 

It's probably the gas cap then, when it seals the light goes off, but when it doesn't for a brief period the light comes on. The cold temps probably aren't helping.

If it's not the gas cap then it's probably some hose that is also old and leaking.

 

Here is a link to a thread to another XJ owner with the P1495. It's a 99, but the guts of the emission system should be identical.

https://www.cherokeeforum.com/f2/tro...-xj-4l-191069/