I have a weird CEL code on my TJ. Ok, a little backstory first. I can't pass smog because the O2 sensor heaters won't go into a ready state. I replaced all 4 sensors. Still nothing. I shot wires and everything looked good. I decided to get a remanufactured computer. I put it in, and now I have a CEL with the code "743h/1859 Undocumented Code". Any ideas?
2001 TJ with 743h / 1859 Undocumented Code
- Thread starter Dirtyjohn
- Start date
@Wranglerfix may be able to shed some light on this.
However, what brand of O2 sensors did you replace them with? If you used anything but NGK / NTK replacement sensors, that is more than likely your issue, as these TJs will reject any sensors other than NGK / NTK and the CEL will not go away.
However, what brand of O2 sensors did you replace them with? If you used anything but NGK / NTK replacement sensors, that is more than likely your issue, as these TJs will reject any sensors other than NGK / NTK and the CEL will not go away.
It was either NGK or Denso. I will have to find my receipt to be sure. The weird thing is that I did not have the CEL with the old computer.
Yes, definitely double check on the brand.
However, that is odd about the PCM causing this new code.
That's why I tagged @Wranglerfix in this. He's the PCM expert with these things, so he will know for sure if a replacement PCM can cause such a code. Hopefully he chimes in soon.
However, that is odd about the PCM causing this new code.
That's why I tagged @Wranglerfix in this. He's the PCM expert with these things, so he will know for sure if a replacement PCM can cause such a code. Hopefully he chimes in soon.
Ok, they are definitely Denso O2 sensors. Could that be why my O2 heaters are not reading as ready? As far as the CEL is concerned, it looks like I was sent the "wrong" PCM, and I am getting sent a different one.
I apologize for chiming in late.
Please let us know what happens when your receive the correct pcm.
Do you have your old pcm? We can attempt to repair it for you if you’d like.
Send me the part number and I will give you a cost to repair if you would like to go that way. (A lot of people keep backup pcms just in case...)
Thanks and enjoy your weekend!
Mark
Put your old PCM back in with NGK sensors. See what happens and report back
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