I have a very basic question(I think) regarding computer error codes and "I/M Monitors" or Inspection maintenance monitors. My question is simple, Why? Why does your automobile select a random number of emission system functions to monitor. I am a noob in regards to computers and error codes so I may be overlooking something very basic.

I recently bought a cheapo code reader from Auto Zone(ACTRON CP9125) and I am using it on my 2000 Dodge Ram Club cab 2x4 w\318.No errors are being read from my vehicle but near the end of the test the device displays a set of 6 "Internal Maintenance Monitor" codes. The manual for the device shows a possible 11 of these monitors (MISFIRE,COMP,FUEL,CATLYST,HTD CAT,EVAP,SEC AIR,A/C,O2 SNSR,O2 HTR AND EGR). When data is collected from my automobile only 6 of these are displayed. 3 are in the "ready" state(MISFIRE,COMP,FUEL) and 3 are in the "Incomplete" state(O2 SNSR, O2 HTR and CATALYST). Are these six monitors the only ones available on my vehicle or is there something else going on here. I would suspect that all 11 would be "ready" or "Incomplete". Why DONT the remaining 5 items(SEC AIR, HTD CAT, EVAP, EGR and A\C) show up on my code reader and why DO the 6 show up?

Again, I am sure my understanding about WTH i am doing is at fault here so go easy on me. I did unplug my battery for 2 hours and used the erase function on my code reader trying to understand my above problem. I believe the incomplete items are due to me loosing the historical data related to each.

The model number of my code reader is the ACTRON CP9125.
Thank you!
PA

 

There are some functions that the PCM monitors for a predetermined number of cycles. And example is the 3-4 shift. It sets a count register when it first slips, and when the count = 7, it sets the CEL. Don't know the reason for the logic being written as it is, but it is done in programming.

Also, some of the cheaper code readers may not show stored codes and some do.

Incompleete state may be that the PCM has not seen the data it is looking for yet, such as O2 sensor. Dreractual has done several posts on O2 sensors and how the PCM handles them from start up and the delay to reading I believe. Too technical for me to really want to read up more - unless I start having problems in those areas.

 

Do the 6 I/M Monitors being displayed by the code reader mean that I have or have had in the past a problem in that monitor? (Ex. O2 SNSR, O2 HTR, COMP, FUEL, MISFIRE and CATLYST).

Also I forgot to mention that my MIL is "Off" and the CEL only comes on when I start the car and turns off promptly.

 

Everytime the battery is disconnected, the PCM forgets everything it ever knew about how your engine runs, and has to relearn it all. (it simply operates from it's base tables.) The monitors want to see a specific number of drive cycles under set conditions before it determines that yes, things are as they should be, or, no, things are NOT as they should be. Each time the battery is disconnected... or goes dead, all those counters are reset, and you start over again.

Some of the circumstances the PCM looks for are pretty esoteric...... so, if you don't do any highway driving, for instance, some of your counters may rarely, if ever, be incremented, and display an "incomplete" status.

 

Thank you, I dont know why I am having trouble with understanding this but it has to be some bit of information im missing. Maybe if I re-phrase my question we will think of it differently. If the code reader tells me that 6 monitors are "ready" it is my understanding that my computer or PCM has enough information to give the code reader pass or fail codes related to that monitor. For example if the reader says "O2 SNSR" is "ready", my oxygen sensor is probably ok. Now, in the manual for my code reader there are 11 possible "I/M monitors" available. If my trucks computer is telling the code reader that only 6 monitors are "ready" what state are the other 5 monitors in(SEC AIR, HTD CAT, EVAP, EGR and A\C)? Please see my prior post for the other monitors.

I drove the truck since my first post and all 6 are now READY with none showing INC(Incomplete). Originally I had 3 incomplete and 3 ready.

 

If they aren't in the "ready" category, they should be incomplete. If they show "ready", and you aren't getting any codes pertaining to that particular system, then as far as the PCM thinks, those systems are working properly.

It is entirely possible, to have a failed sensor, that the PCM does NOT pick up on, as it is giving data that is in the 'correct' range, but, the data itself may NOT be correct. (O2 sensors are famous for this)

Some of the monitors will NEVER show ready, as your truck is not equipped with those systems. EGR being right at the top of the list. No Air injection on your truck either, so SEC AIR will never be ready either.

You DO have EVAP though, and why that one doesn't wanna be 'ready' is probably related to my above post. (not enough drive cycles where conditions are met for the PCM to judge.)

 

Thanks HeyYou, Im a little slow responding. I had back surgery yesterday and im feeling a little broken. Thanks for helping me understand this. I'll try to update this post a few more miles down the road.

 

This explains alot, ive always wondered what those meant on my code reader. I have numerous lines for my evap system that were broken and then "rigged" and probably still leaking. I get a P0441 code every so often (incorrect purge flow)

/sorry for thread jacking

 

This part is perfectly normal. It is checking the system while the CEL in on, and then clears once it verifies that everything is OK.