1994 Mazda B4000 4.0V6 (O2 PCM not responding)

Hello, I am working on a 1994 Mazda B4000 4.0V6 (basically a Ford). B2S1 is reading voltage from .1 to .9 like it is supposed to read for lean and rich switching. But on B1S1, the O2 sensor either reads up to .1 to .2, but usually 0.00. I used a test light on B2S1 and went to ground and I got 0 volts & I went to battery positive and got 1.22 volts which means that signal wire is good. The issue is the B1S1, when going to battery positive I only get around .4 to .5 volts. I even back probed at the PCM and got the same results.....

Not looking good for the PCM. Just to make sure, you had the B1S1 disconnected while applying the test light? Did the bulb illuminate at all when applied?

the test light method burnt me on a newer transit awhile ago. so i dont solely rely on that test as 100%. usually what ill do in a case like this is to be more certain is either switch the pins at the pcm OR pierce the signal wire on the known good and run a jumper wire to the one in question pierce the signal wire on that one to and feed the signal in that wire and check scan data

I tried it both ways and got the same results as far as being connected & disconnected & the test light never did light up, but never light up on either bank either. Its weird that bank 2 reads 1.22vdc when using the test light, but bank 1 reads on .500vdc when using the same test light to battery positive. I started at the O2 connector and went to one other connector and eventually back probed directly into the PCM and all the same .500vdc.

I ran a jumper wire from the signal wire to the pcm and got the same .500vdc results.

BLEE wrote: I tried it both ways and got the same results as far as being connected & disconnected & the test light never did light up, but never light up on either bank either. Its weird that bank 2 reads 1.22vdc when using the test light, but bank 1 reads on .500vdc when using the same test light to battery positive. I started at the O2 connector and went to one other connector and eventually back probed directly into the PCM and all the same .500vdc.

Thanks for the clarification! It sure looks like you have a PCM issue to me. You can also do what Cheryl suggested, as far as connecting the bank two O2 signal into the bank one circuit. You could also check the bank one signal circuit for continuity to ground with your multimeter (with the PCM and O2 disconnected). Obviously, there should be none.

Beyond that, you can verify PCM powers and grounds, mostly as a matter of course. You can also try a soft reset by disconnecting the battery cables and shorting them together for awhile. It's a long shot, but I've fixed some strange computer problems this way.

makes two of us with pcm issues. having a pcm issue on a 2013 f150 5.0 battery drain of 4.5 amps. found the pcm power relay staying on. cut the wire at the pcm it quits grounding it. need to check the feeds coming in. them ford.....

Thanks again. I switched the O2 harness connectors and #2 still reads & #1 still does not read. I did a short to ground and it is good to go. I checked the signal wire #2 and #1 from PCM signal to PCM ground and got the same resistance.