Topic: Really annoying codes.

[van]

OK, so I picked 3 ecm codes several months ago, 2 21s (o2 sensor) and a 72 (cat efficiencey-I hate the flashed ecm).  I replace the rear o2 sensor, reset.  One 21 comes back and that's it.  I replace the front o2 sensor, all is good for a few miles.  I pick up a 51 and both 21s are back.    Any thougths?  Could I be running so lean as to cook the o2 sensors in 30 miles or so?

[Dylan]

Maybe an exhaust leak creating a lean condition at the O2 sensors?

Pull your plugs and see how they look to verify if you're actually running lean.

[sharpxmen]

OK, so I picked 3 ecm codes several months ago, 2 21s (o2 sensor) and a 72 (cat efficiencey-I hate the flashed ecm).  I replace the rear o2 sensor, reset.  One 21 comes back and that's it.  I replace the front o2 sensor, all is good for a few miles.  I pick up a 51 and both 21s are back.    Any thougths?  Could I be running so lean as to cook the o2 sensors in 30 miles or so?

since you replaced both i am thinking you might have a bad sensor ground. the 51 (and even 72) could be a result of that. the voltage reference would be off in that case, you should measure the sensor ground to PCM resistivity with a multimeter (from the O2 sensors ground wire to the PCM sensor ground pin). Not sure what you mean by "flashed ecm" so maybe you can give some info on that and also what year is your Jeep (i assumed it's a '97 since you have the 2 digit codes and 2 O2 sensors)

[van]

since you replaced both i am thinking you might have a bad sensor ground. the 51 (and even 72) could be a result of that. the voltage reference would be off in that case, you should measure the sensor ground to PCM resistivity with a multimeter (from the O2 sensors ground wire to the PCM sensor ground pin). Not sure what you mean by "flashed ecm" so maybe you can give some info on that and also what year is your Jeep (i assumed it's a '97 since you have the 2 digit codes and 2 O2 sensors)

It is a 97.  I replaced the rear first, and that resulted in only one code.  I replaced the front, and got 2 codes again, and the 51.  I'm guessing it really is running a bit lean as I burn through a header every 2 years or so.
With respect to the ECM, somewhere around 2007 I think DC had a tsb where they "fixed" the ecms to actually throw 72s for converter efficiency.

Is the ground switched? i.e. check it on or running or off?

[sharpxmen]

It is a 97.  I replaced the rear first, and that resulted in only one code.  I replaced the front, and got 2 codes again, and the 51.  I'm guessing it really is running a bit lean as I burn through a header every 2 years or so.
With respect to the ECM, somewhere around 2007 I think DC had a tsb where they "fixed" the ecms to actually throw 72s for converter efficiency.

Is the ground switched? i.e. check it on or running or off?

you need to check the wiring, so no real ground necessary - measure the resistivity between the sensor ground wire (at each sensor) and the wire going to the PCM (on the connector on the wire harness side, while you're at it you can check the status of the connectors as well and maybe use some contact clean on the wire harness side) - the sensor ground is different than the vehicle ground. I can't help you with the location of the wires as i have a YJ but you should be able to do a bit of a research and find out the colors (on YJ if i remember correctly the senor ground is black with a light blue strip). the reason i am thinking it could be this is b/c you replaced both sensors and you get codes from both - but there are other reasons that can cause this, like you said the mixture can be off and then the PCM would trigger some codes.

[van]

Props to sharpxmen.
I had some worn wiring to the front sensor which was shorting out. (apologies for the pace at which I fixed all this....)
I have a new/old DD again.

Of course, my radiator is almost shot now, and if I rip that out, I should probably go electric fan, and....

[sharpxmen]

Props to sharpxmen.
I had some worn wiring to the front sensor which was shorting out. (apologies for the pace at which I fixed all this....)
I have a new/old DD again.

Of course, my radiator is almost shot now, and if I rip that out, I should probably go electric fan, and....

cool man, glad you got it sorted out