Not charging, no CEL or trouble codes

[Marcucco]

1996 XJ se with a 120 amp alternator upgrade. It has been running fine for a year and a half.

The alternator isn't charging, there's no CEL or stored trouble codes in the PCM

I pulled the alternator and it benchtested as good.

The battery and all the connections (checked twice), all are good, including grounds. Belt tension is good.

The Batt temp sensor has 20K ohms, the FSM says it should be 11K @ 70º but it's about 40º here now.

I'm only getting a little over 1 volt at the ASD relay terminal.

[Skwerly]

"Bench tested." At an AutoZone or something?

[techno1154]

9 to 11 oms at 75*. The resistance should be higher at 40* which would increase the charging voltage until the battery heats up. A bad sensor in itself should not prevent the alternator from charging. Just for kicks, unplug it and see it conditions changes.
My theory is that you have one of two issues,... your alternator or the PCM. There is a way to test the alternator without removing it with the engine running.

[Marcucco]

Skwerly: O'Rielly's ran the test.

Techno1154: I did try starting with the bat temp switch unplugged (which I think should have caused an error code but didn't.) But I don't see 20 ohms at 40º being an issue.

Since it's not charging and I'm not getting a "GEN" light or any sory of an error code, I think I may be going for an ECM, but I'l do a bit more digging first

[techno1154]

I did not think it would make a difference regarding charging or not charging. When I run mine with it unplugged I get error 1492 after about 10 minutes Charging remain about 13.5 volts with it unplugged and plugged in just over 14 volts.