I got a 1994 Jeep Cherokee 4.0 Ltr., & I wen't to go to emissions the other day to have it fail only on my Nitrogen Oxide test. The limit was 3.00 & I got it up to 3.90. So, I'm asking what it may or may not be. I'm thinking it's my O2 sensor, but I'd like an educated opinion on the matter. Thank you!

 

Check egr system very thoroughly

 

Try a reset of the ECU Reset and try the test again.


1. Disconnect the battery by removing the positive battery cable. Remember, the positive battery cable.

2. Ground the positive cable to the negative cable for 30 seconds to erase the electric charge in the capacitors.

3. Reconnect the positive cable to the battery.

4. Turn the key to on but do not start.

5. Turn the headlights on.

6. Turn the headlights off.

7. Turn the key off.

 

I didn't think there was a EGR on the XJ's after renix systems were discontinued.

 

What does turning the headlights on and off do?

 

Drain the capacitors inside the PCM and resets it to learn mode. Same thing can be accomplished by unhooking the battery for a day.

 

Has the Jeep been scanned for any codes? Or they key trick used to get the CEL to flash?

When was the last tuneup with spark plugs?

 

That crap ended in 1990.

 

If you failed NOX and only NOX it's probably not a sensor issue. High NOX is a sign of excessive combustion temps.