Well the other day I got a "Check Engine" light while driving. After cycleing the ignition switch 3 times I found the #21 code was the reason. I replaced the O2 sensor and still get the #21 code. The check engine light does not come on untill the truck (94 Ram 5.2) is up to temperature. This is exactly the same as before the sensor was changed, also it the "Check Engine" light turns off after the truck cools off. And I left the battery disconected for at least 2 hours, any ideas as to what could still be creating the fault. Oh and by the way the truck has 55,000 miles and runs perfect.

 

Did you try to reset the pcm by disconnecting the battery and turning the key to the start position for about 15 sec? I would say check the cat, but with only 55K miles it should be okay.

 

That was the next thing I was gonna try, thank's for the response. I'll let you know how it works.

 

Reseting the PCM didn't seem to work, I read somewhere that if the 21 fault shows and a new O2 sensor doesn't do the trick that it may be the PCM itself. I have a PCM for a 93 (one year older) same engine and transmission, does anyone know if it will interchange? By the way the truck it came from really flew, it was a SWB reg cab 2wd and had a MOPAR performance PCM, Flowmaster muffler, 160 t/s and a 14" open element air cleaner. It ran mid to low 15's 15 years ago.

 

I really don't know about the PCM interchange. I think a '93 would be a 1st gen. Ram, so I don't if anything is different in the beginning of the 2nd gen. Maybe someone else will chime in...

 

2nd gen is 94 to 01, you should be ok. Plus it can't hurt to try it. But you should trace the o2 wires back to the pcm and make sure they are ok. And also make sure the cat is good.

 

The PCM he has is for a '93 and he wants to put it on a '94. But, yeah, I agree it can't hurt to try.

 

Sorry, read it too fast. They are both OBD1 though. With the possibility of some different sensors it still might work.