Self diagnostics, or get scanner?

I have a 96 Cherokee and have been getting a code 72, using the 3 times on/off ignition trick and reading the CEL flashes. Code 72 in the haynes says CAtalytic converter circuitry...bring to dealer (more or less). Will hooking it up to a fancy code reader/scanner like the ones at autozone give me any more detail? If an 02 sensor was bad I would think it would say so by flashing the proper code.

A fancy scanner will give you the same thing 72.
It telles your there is a problem and now your need to find it buy testing the voltages and wiring.
If all that checks out then the sensor could be bad.
Codes don't mean the sensors bad, it just a place to start trouble.

GOJEEP has some pretty good code lists on his site. I've found the wiring burnt on the rear O2 sensor a bunch of times. Usually the first place I look.

Ummm some of us are avid users of REAL scanners and we dont believe in just reading the codes .....yes you can get way more detailed info ,say from a snap on modis like I use daily I can graph you o2 sensor on a built in digital storage scope for your viewing pleasure and no I wont do it for free like they do......its your choice get a slight clue, or get the info you need.You can buy thier junk scanner for around 30 bucks or spend several thousand for a real one .....or go to a real shop....further more if you dont actually know what a "fancy scanner" will do for you please do not pass along your unfounded assumptions about them to others

deskjockey said:

I have a 96 Cherokee and have been getting a code 72, using the 3 times on/off ignition trick and reading the CEL flashes. Code 72 in the haynes says CAtalytic converter circuitry...bring to dealer (more or less). Will hooking it up to a fancy code reader/scanner like the ones at autozone give me any more detail? If an 02 sensor was bad I would think it would say so by flashing the proper code.

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Hey desk jockey, I would lay odds on a lazy front o2 sensor fooling the ecm into thinking the converter is faulty (if this is the code that pertains to catalytic efficiency, im just going by memory here in the redbeer laboratory) but the only true way to tell is to graph the o2 sensors together and compare charts then use a gas analizer to monitor what the converter is doing or temp gun the converter and see if it gains temperature (about 100 degrees from inlet to outlet) there are several ways to find out conclusively whats going on but only a few will give you the right answer every time ......dont go to some dumb parts chain for correct answers they sell parts and we repair facilities ......we do just that ...thats why we dont use junk generic scanners our "fancy ones" give us alot more that a mere clue. ever see a parts chain scanner have a 5 gas analizer? graghing capabilities?..ha ha no way dude!

majic_tech said:

Hey desk jockey, I would lay odds on a lazy front o2 sensor fooling the ecm into thinking the converter is faulty (if this is the code that pertains to catalytic efficiency, im just going by memory here in the redbeer laboratory) but the only true way to tell is to graph the o2 sensors together and compare charts then use a gas analizer to monitor what the converter is doing or temp gun the converter and see if it gains temperature (about 100 degrees from inlet to outlet) there are several ways to find out conclusively whats going on but only a few will give you the right answer every time ......dont go to some dumb parts chain for correct answers they sell parts and we repair facilities ......we do just that ...thats why we dont use junk generic scanners our "fancy ones" give us alot more that a mere clue. ever see a parts chain scanner have a 5 gas analizer? graghing capabilities?..ha ha no way dude!

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So Dude...how far are you from Northport, Alabama? :doh: or can you recommend some one around here with your skills??? I'd love to find a mechanic I could trust, and that I actually think new more than me about my truck! Maybe you wanna think about relocating? Not much snow down here...although I'd like an occassional snow! :wave:

No i aint from alabama but i was born close to there. the monitary benefits down there suck big time.......

Is there a sort-of-fancy scanner thats worth having?
What features to look for..? I want to at the very least see the "P" sub-codes that
are listed in the FSM.

you can see the p codes on a snap on modis scanner and actuate all the stuff a drb can. also graph most every sensor on the beast they have all kinds of neat stuff like optional 5 gas analizer bench really too much to list here.....see you friendly neiborhood snap on dude for further details .....ohh and have lots of cash with you when you do........were not talkin some $30 garbage from a national parts chain here were talkin several thousand dollars thats why more people dont own them....................

I do a quick cost efficiency study. A typical trip to the dealer costs about 20% of my yearly gas bill. They actually fix what was wrong, less than fifty percent of the time. I keep track of my gas mileage and program a trip to the emission tester, every two years (around here).
Just a WAG, (wild arsed guess), but many of the sensors are daisy chained. The TPS can cause the MAP to go out of the envelope (slightly), that can generate a enough of a rich/lean burn condition to cause a conflict between the front and rear O2 sensors. It could also be a flaky cat. they are designed to last for 7 years, typically start to fail around 130,000 miles.
Another part of your cost efficiency study has to figure in, what your time is worth. My pay has never approached what a dealer charges per hour. Checking wiring and connectors is time consuming.
The price of a fuel control sensor package (Engine temp sensor, MAP, TPS, O2 X2) just about equals the cost of a trip to the dealer (if he doesn't fix anything). If they actually fix something and they are right 50% of the time, a typical bill may equal closer to 40% of my yearly gas bill. My percentages actually work with most any gas bill or yearly mileage. The costs rise significantly after 130,000 miles of vehicle use. Off road use can easily double the numbers.
I'm not saying an in depth scanning is useless, just saying it gives you more symptoms for a condition, that may help in a diagnosis or may not. Many of the questionable sensor values can be traced to resistance in the wiring or a mechanical problem in your motor or related sub components.
I always check the motor basics and the wiring before going anywhere near the dealer.
The boards can help by using somebody else's solutions. Problems tend to repeat themselves.

Im not talking about a dealer man just a competent shop. I dont work for a dealer I think most of them are a shame ive worked at a few as far as guessing and throwing parts at it, its your money spend it as you wish I can give you a real answer for 23.00 an hour less than the dealer ........ask around people will tell you who you can trust.....I can guarantee you the answer aint gonna come at a parts house by them telling you anyway....and concerning your o2 conflict it aint gonna happen that way dude (what about adaptive limit codes ,what you described would set one of these) both o2s see the same gas its the second one than should see less oxygen than the first if the converter is functioning properly....trust me I live in an e test area and I have to make them pass so i know how they work...............Im jusy trying to say dont go slamming on those fancy scanners thier truly bada$$ .....Theres alot of new technology out there now, find a place that has it and when all guessing fails turn to them

I wasn't slamming testers either, was just suggesting that motor basics, wiring and engine controls are a package. And checking the basics before an expensive trip to whomever, might save some money, if you have the time.
I'd love to have access to a good tester and somebody who was competant in using it.

So far with my knowledge of scanners and the turn key method is that the turn key will give you a general code as to what the problem is where as the scanner will go into detail. For instance, i had an injector wire problem and the turn key method said fuel injector control circuit, where as the scanner pin pointed the problem to injector 5, from there i was able to figure out the problem by focusing all my attention on the #5 injector instead of all 6.