Hey everyone, I’ve been trying to figure out what’s keeping my 1988 MJ stuck in open loop but I haven’t been able to find the reason. On my REM after it warms up it’ll show that the voltage is moving a little bit (when it’s cold it stays at 4.98v) but I keep getting an error code for O2 heater voltage low. I checked the orange wire at the connector with it running and it showed 13 volts, also I put in 2 brand new sensors to see if they’re the issue. I checked the manifold bolts and they’re all tight and it has brand new vacuum lines. On NickInTime’s website it says that it could be caused by the ECU being stuck in WOT mode, how can I check to see if that’s the case?


Also here’s a video showing the numbers and the code:
https://youtu.be/IFvWOLZX0jc?si=wUhDDe6R0WA2p8uC

 

Have you ever visited my website and completed Tips 1 through 5?

 

Yes I have, I also did the ground upgrades that you recommend and the previous owner did the C101 connector delete. I still need to clean out the relay box, after I do that I’ll report back and let you know if that fixes it. Is there anything else that I should check while I’m there? Also if it were to be the relay would it still send 13v to the orange heater wire at the O2 connector?

 

Don't second guess. Clean the relay box.

what if the O2 sensor ground is bad? 13 volts isn't gonna light up the heater if there is no ground!!!

 

Will do, I’ll report back tonight

 

I can’t believe it was that simple. Goes into closed loop just fine now, thank you so much!

 

what did you do?

 

Cleaned up all of the relays and the relay box.

 

NICE!!!!

It pays to COMPLETE all the Tips, eh? LOL. Thanks for reporting back.

 

I can amaze myself with my stupidity sometimes

 

Don't be too hard on yourself. Many folks think the tips are bull****. Can't be true. It's gotta be some failed component. Computer issue.

We know better.

 

new here, been looking for wiring diagrams and other information due to no blower motor power and blinkers work sometimes.....then wont.....could push on fuse block and would kinda work......gonna hit all your tips b4 proceeding any further.....89 mj 4.0 manual transmission