Blackxj51

My 1999 xj 4.0 auto is due for emissions and it failed twice now, first because I had the battery unplugged right before I took it in and the readiness monitor wasn't ready yet and second it failed because it said the state computer couldn't connect to my obd on the jeep, any ideas why this would happen?

quneur

Make sure all sensors are ready. Some sensors take quite a few miles to be ready. Get a code reader or borrow one from an auto parts store. If the reader recognizes your vehicle and reads a few sensors in a ready state then its not the OBD2 system in your car.

If there are sensors 'not ready' state it should also tell you. Drive around more and check it again. Took me three days of local driving to get all my sensors into a ready state.

Fred/N0AZZ

Unless someone has hacked it the 99 had OBDII connectors under the dash. Drive it for a while then run by an auto parts store and have them put there code reader on it and see what they say about connections and codes.

Blackxj51

I drove it around for about 75 miles and did the second test and it showed at least 2 readiness monitors ok which is the requirement and it still failed due to connection issue, though I drove it an extra 200 miles this weekend and checked it with my code scanner and it says I have a code for catalytic converter efficiency and did a live data test confirming my cat is bad but my check engine light isn't lit up, now I pulled the panel off under the steering wheel and a box fell out with wires spliced into the harness underneath, looked like some kind of security system someone tried to rig, I disconnected it from the wiring harness and taped up all of the bare wires but the cell still isn't illuminated, is there a fuse that could've been blown by this security box I pulled out that would cause the cell not to illuminate, I'm gonna check for a bad bulb tomorrow

EZEARL

Even though there is a malfunction in a monitored circuit unless certain criteria are met a fault code won't be entered into the computer memory so the CEL won't be lit. I ran into this when I was having IAC and CTS issues.

Blackxj51

Would the computer connection issue be because it hadn't been able to ready that efficiency code yet because I hadn't driven enough miles though?

EZEARL

I can only guess no. Reason I say that is because I recently took a 300+ mile round trip in which my gas mileage bottomed out. Replaced both o2 sensors when I got home and just driving around locally I can see a big difference. No CEL and no codes. When my low idle/no fast idle when cold issue happened I drove it a few days until my parts came. No CEL and no IAC code but did have a CTS code show.