Wacky OBD code

[Mike in NJ]

"72" ????

It's a '96, 4.0.

Now, I always assumed that, because I can get codes through the ignition key sequence, I have an OBD-I system like my '92. Trouble is, there is no "72" (no seventy series at all).

Now, I understand that OBD-II was mandated from the '96 model year, but that is a four number code. And I thought that list required a scanner. And we all know that XJ's don't necessarily have what each year is supposed to have.

"0072" is "Ambient Air Temperature Sensor Circuit Low Input" - whatever the hell that does. Trouble is, I still don't buy the four digit answer. I get a perfect OBD-I result: 12-72-55

But, there is no "72". :cry:

Mike in NJ :patriot:

[Rob Mayercik]

Mike, I was just lurking about Marcus's site (GoJeep), and pulled up his fault codes how-to.

He has three different lists there, and the first and third show a "72" code. Judging by the descriptions, I'd say the first list is for your '96.

That list shows 72 as "catalytic converter circuit", and is explained as "needs specialist or dealer diagnostics". Maybe a sign of a dying cat?

Here's the page: http://www.go.jeep-xj.info/HowtoECUcodes.htm

HTH,

Rob

[Beezil]

Code 72 means a safty code violation exisits.

does this vehicle have a first aid kit and fire extiguisher?

better go to the jeep dealer on this one.

[Digger87xj]

MIL code 72 is equal to OBDII code PO420. catalyst efficiency failure.

Your cat is failing. Only repair is to replace the cat.

[ZmOz]

Yes, your XJ is OBDII and no, you don't need a scaner to get the codes.

[Mike in NJ]

That list shows 72 as "catalytic converter circuit", and is explained as "needs specialist or dealer diagnostics". Maybe a sign of a dying cat?

Thanks Rob (and Digger). Makes sense now. Couple of years ago, my cat DID die, but when I got the replacement, there was no bung for the 2nd O2 sensor. Figured that the one on the cat didn't actively control anything (other than a comparative reading), I just left it off. Got a "21" code then (O2 sensor signal doesn't change) and just taped over the check engine light.

It would have failed NJ inspection though, so last month we cut a hole in the rear of the CAT, welded in a bung, and re-attached the O2 sensor. Light went out and I passed inspection. "72" showed up yesterday - I guess the homemade O2 sensor positioning didn't work permanently. The cat only has about 15K on it, so I'm assuming it's still OK.

Time for tape again. At least I didn't get to the point of replacing the MAT sensor (Code P0072). Thanks Z for the OBDII comment.

As for Mr. B - you think "I" have a safety violation? - give it a month and wait until Prez gets ahold of your rig for NACFest inspection! :lecture:

Later,

Mike in NJ :patriot:

[JoBo]

Mike, I was just lurking about Marcus's site (GoJeep), and pulled up his fault codes how-to.

He has three different lists there, and the first and third show a "72" code. Judging by the descriptions, I'd say the first list is for your '96.

That list shows 72 as "catalytic converter circuit", and is explained as "needs specialist or dealer diagnostics". Maybe a sign of a dying cat?

Here's the page: http://www.go.jeep-xj.info/HowtoECUcodes.htm

HTH,

Rob

On my 96 there's a o2 sensor on the rear of the cat.

JoBo

[Onkover]

72 is one code I don't know off the top of my head but the other one..

12 = the computer memory has been reset in last 50-100 starts
55 = end of message

The only code I would concern myself with is the 72.