Vermonster01

Hey, So my check engine light came on and I believe it is a bad O2 sensor, is there a way to tell without and equipment?

94XjSport94

Go to a auto parts store and have them read the code

CCKen

You may want to check the Oxygen Sensors Heaters fuse in the PDC.

Vermonster01

What would I be looking for about it?

Vermonster01

Cant, Its not inspected currently.

CCKen

Remove the Blue 15 Amp fuse marked "O2S Heaters" and see if its blown.

94JeepCherokeeMan

Cycle your ignition on-off-on-off-on in three seconds and your CEL will spit out any codes you have. You may have to do it 5 times, but stop at "on." In the 97+ Jeeps, it may do it on your instrument cluster. A code 21 is an O2 sensor problem in the older Cherokees, not sure about 97+.

Vermonster01

Ok, So I got Three different ones, One is 12 then 11 then 21 what do they mean?

salad

What year XJ do you have? 1996+ should give you four-digit codes like P0301

DFlintstone

I think "after the change", the key trick only gives info for the dash, or cluster. You need a reader.

"the change" might have been sometime in 97. If he's getting 2 digit codes they are "keyed" in info threads on page one here.

When my (pre 91) Renix 02 was dead, it would idle a bit, slow sown, nearly stall, rev slightly then even out and repeat every 25 seconds or so. One or two other Renix guys have found/replaced their bad 02 that way. (titinia sensor there) So far no OBD guys with Zerconia sensors have mentioned anything like that.

Below is something I saved last year...(no Idea why the discrepancy in years)

You can try this. I hear sometime in 97 it no longer works.
1984-1990 w/AMC engine are pre-OBD.

1984-1986 w/GM V6-173 are OBD-I (GM control setup.)

1991-1995 are OBD-I (Chrysler)

1996-2001 are OBD-II (Chrysler)

The "Key Tricks"
Older (OBDI) models - Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. ("On" is NOT "Start" and "Off" is NOT "Lock"). The "check engine" light will flash. Count the flashes. Each code is a two digit code, so a (for example) 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). It will never flash more than 9 times, so watch for those pauses!

Newer (OBDII) models - Put the key into the ignition, push down the odometer reset button, then turn the key to RUN with your finger on the button - and then release the button. The odometer will go through 1111111 through 999999, then display the car's serial number. It will then show the error codes (it might show them starting with P). If this method does not work, try the OBDI method.

94JeepCherokeeMan

12 is a battery disconnected within the last 50 startup cycles, 21 is a faulty reading from the O2 sensor, and I can't remember what an 11 is.

94JeepCherokeeMan

11 is, unfortunately, a no crank signal to computer. This may be related to your CKP (Crankshaft position sensor). Here's a great link to some computer codes. 97 uses the same codes as the OBDI generation.

http://jeep-xj.info/HowtoECUcodes.htm