97 TJ with code 21

BrunoPizz97

BrunoPizz97

TJ Enthusiast
Joined
Jul 11, 2019
Messages
408
Location
Long Island
So when I first got this Jeep I got a check engine light the next day and the code that popped up was code 21. I did the key trick to see the code I know it has something to do with an engine misfire, the car was not running right so I brought it in to the mechanic and he said one of my injectors failed. So he swapped that out and bam it didn’t sound like a van struggling to get the wheels spinning. So 5 months to today, I was driving to work and noticed my CEL come on when I parked, now the car doesn’t sound anything like it did before it’s running completely normal the light isn’t flashing so I know it’s not multiple misfires like before. Has anyone had this problem, has this been solved before?
 
Chris said:
That’s an O2 sensor related code.

Do the smart thing (I’m not kidding either) and replace all of the O2 sensors at once.

The part numbers for the correct NTK / NGK sensors can be found here:

https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/
Do not use anything but NTK / NGK sensors.
Click to expand...
His TJ only has two sensors and the second downstream O2 sensor only monitors the catalytic converter. It has no effect on the engine, air-fuel mixture, etc. like the upstream O2 sensor does on earlier TJs like his. If it were me I'd replace just the upstream O2 sensor for his problem.
 
  • Like
Reactions: Chris
Hey @Jerry Bransford, while we’ve got you talking about ‘97 4.0 O2 sensors, what do you make of this?

Pulled my belly skid off to do some maintenance and while looking around saw an O2 sensor near the top of the cat (pointing at TC) and this second one highlighted by penetrating fluid I sprayed before dropping the skid. Wires have been cut, and I can only assume have been that way for a long time. The Jeep runs fine, no check engine lights, haven’t checked codes lately, but is usually fine. We don’t have smog testing here.

This is the main cat right? If not both O2 sensors, what else would I be looking at?

714F58A4-7998-4B76-9DC5-4002E1F6EBD9.jpeg

7F327D7A-8575-4C7A-BADD-5C6A33059E7D.jpeg
 
I dunno, everything looks upside down there, I had to turn my phone upside down. 🤔😁 Actually I've never seen two sensors screwed into the main catalytic so your second sensor is a mystery. It doesn't look like an O2 sensor to me either, a temperature sensor is a good guess. . Does NZ have its own set of extra strict smog laws like I do here in California?
 
I've read through the FSM and parts guide and couldn't find anything either.
We have no Smog testing at all, so won't be related to that...

How interesting!

I glossed over it yesterday as I was focussed on other things. I'll check it out tonight, I might be able to tell if the weld in bung looks factory or not. Export models may have used a different cat that had the sensor in there for another application, who knows. I'll let you know my findings
 
  • Like
Reactions: Jerry Bransford
Jerry Bransford said:
His TJ only has two sensors and the second downstream O2 sensor only monitors the catalytic converter. It has no effect on the engine, air-fuel mixture, etc. like the upstream O2 sensor does on earlier TJs like his. If it were me I'd replace just the upstream O2 sensor for his problem.
Click to expand...
Just bought the sensor, I was really surprised; it was super cheap. I will let you know if it fixes my CEL. So far it has not went away on its own, and every time i cold start it sputters and sounds like i have a cammed 4.0L I6
 
BrunoPizz97 said:
Just bought the sensor, I was really surprised; it was super cheap. I will let you know if it fixes my CEL. So far it has not went away on its own, and every time i cold start it sputters and sounds like i have a cammed 4.0L I6
Click to expand...
Super cheap? Hopefully you installed the recommended NTK brand and not Bosch. Also, disconnect your battery's negative lead for 5 minutes to reset the PCM so it will relearn the new upstream O2 sensor. I hope you didn't end up with a Bosch.
 
Jerry Bransford said:
Super cheap? Hopefully you installed the recommended NTK brand and not Bosch. Also, disconnect your battery's negative lead for 5 minutes to reset the PCM so it will relearn the new upstream O2 sensor. I hope you didn't end up with a Bosch.
Click to expand...
I bought the NTK from rock auto it was cheaper than I expected and great tip i wouldn't have thought of disconnecting my battery
 
  • Like
Reactions: Jerry Bransford
Jerry Bransford said:
Super cheap? Hopefully you installed the recommended NTK brand and not Bosch. Also, disconnect your battery's negative lead for 5 minutes to reset the PCM so it will relearn the new upstream O2 sensor. I hope you didn't end up with a Bosch.
Click to expand...
so I fixed the o2 sensor and now i am getting another code
Code 43: cyl 6
 
Top Bottom
Back