I recently took my 99 cherokee Sport in to have it inspeted and was troubled to learn that I has 4 malfunctions on my computer. The DTCs page reads as:

Since DTCs Cleared
--------------------
Catalyst Mon inc
Evap System Mon inc
Oxygen Sens Mon inc
Oxygen Sens Htr inc

I was wondering if any could tell me what these codes mean and why I might have so many? Maybe even how to go about getting rid of these codes so my jeep can pass inspection. My check engine light is not on and my jeep runs fine. But I want it to be flawless. I'm not very good with diagnosing computer controlled cars.

Are all of these things bad or could it be the PCM?

 

This is one way to address it. This method requires patience...

Go to your local chain auto part store and borrow (get help) their scanner. Record the codes and descriptions in the order they report. Address the first one (replace indicated sensor or find broken wire, whatever) then clear the codes (disconnect battery negative for a few minutes then securely reconnect) and drive awhile (with a few on/off cycles along the way). Repeat scan-rework-clear-drive-scan process until you get a clean scan.

Often-times you may find that one (or one of the first few) of the codes can spawn additional codes (domino effect theory) due to PCM making adjustments based on response to first code-set.

 

I own a scan tool, actron autoscanner. I replaced downstream O2 sensor and half the problems went away.

The only things left are: evap system mon inc. and oxygen sens inc.

Now all I need to do is figure out this darned evap system monitor thing. That's something that I know absolutely nothing about.

Can you give me some sort of starting point? Like what sensor I'm looking for? Where it might be located? Or some other part I might be replacing?

 

i didnt bother reading these but perhaps the answer is here:

http://www.google.com/search?q=chero...hrome&ie=UTF-8

 

Those are not codes. Those mean the moniters arent set. If you had the battery disconnect recently, this is what will happen. All you have to do is drive it to get the moniters to set.

 

The evap system is a small pump that pressurizes the gas tank. This keeps fumes from the outside.The gas cap is the first place to check. Next vacuum lines and hoses under the truck near the tank.
These will give you somewhere to start.
Ron

 

X2

Gas cap is the first best cheapest thing to check as the cause for evap codes. The evap lines cluster into the charcoal canister located under driver's side rear near e-brake cable adjuster. Look for cracked plastic lines - that's what I found when I was troubled by evap codes. A smoke test may also be performed to locate leaks if cracks cannot be located but codes continue to set-up (some guys have used very low pressure compressed air then listened for the hiss). Additionally, the evap solenoid is near the firewall passenger side - it's the thing that "ticks" while the engine is running - check those lines too.

 

Ok, probably overkill, but everything has been replaced. New lines, solenoid, gas cap, evap canister, connectors. The only thing I could find during the whole process was 1 tired old connector.

Took it out for 100 mile ride to make sure everything worked. Still have that darned DTC stating that evap system monitor is incomplete.

I checked the gas filler neck, tank, etc. It runs great. Just got the one dtc.

Now what?

 

buy diagnosing factory manual and follow step by step procedure.
There are many smart people here, but they are not substitute for service manual.
Recently some guy got response, that his TPS sensor is possibly bad. Instead of diagnosing it (takes about 1 min), he just replaced it w/o any good results.