Code reader dire warnings about erasing codes.
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Posting Guru
Joined: Jun 2005
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From: Location, Location.
Code reader dire warnings about erasing codes.
Gentlemen,
So I finally broke down and bought me an OBDII code reader. An Autel Maxiscan. Gonna use it on my 2000 Expy to figure out why it keeps stalling when I shift into reverse (after already replacing the transmission filter).
My understanding is that when diagnosing a problem, it's useful to "clear the codes" in order to see what new codes are registered when the event you're trying to fix occurs.
However, under "Erasing Codes", the reader's manual says in big black bold letters:
"CAUTION: Erasing the Diagnostic Trouble Codes may allow the scan tool to delete not only the codes from the vehicle's on-board computer, but also "Freeze Frame" data and manufacturer specific enhanced data. Further, the I/M Readiness Monitor Status for all vehicle monitors is reset to Not Ready or Not Complete status. Do not erase codes before the system has been checked completely by a technician."
Very ominous.
So :
- what the heck is "Freeze Frame" data and should I be worried about erasing it?
- what is "manufacturer specific enhanced data" and should I be worried about erasing it?
- what is " I/M Readiness Monitor Status" and should I be worried about setting it to Not Ready or Not Complete status?
Thanks.
So I finally broke down and bought me an OBDII code reader. An Autel Maxiscan. Gonna use it on my 2000 Expy to figure out why it keeps stalling when I shift into reverse (after already replacing the transmission filter).
My understanding is that when diagnosing a problem, it's useful to "clear the codes" in order to see what new codes are registered when the event you're trying to fix occurs.
However, under "Erasing Codes", the reader's manual says in big black bold letters:
"CAUTION: Erasing the Diagnostic Trouble Codes may allow the scan tool to delete not only the codes from the vehicle's on-board computer, but also "Freeze Frame" data and manufacturer specific enhanced data. Further, the I/M Readiness Monitor Status for all vehicle monitors is reset to Not Ready or Not Complete status. Do not erase codes before the system has been checked completely by a technician."
Very ominous.
So :
- what the heck is "Freeze Frame" data and should I be worried about erasing it?
- what is "manufacturer specific enhanced data" and should I be worried about erasing it?
- what is " I/M Readiness Monitor Status" and should I be worried about setting it to Not Ready or Not Complete status?
Thanks.
Thread Starter
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Posting Guru
Joined: Jun 2005
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From: Location, Location.
OK, found one item - excellent explanation of here:
CanOBD2 - Tech+Info%2cOBD+Knowledge - I/M READINESS
"I/M Readiness shows whether the various emissions-related systems on the vehicle are operating properly and are ready for Inspection and Maintenance testing.....I/M Readiness Monitor Status shows which of the vehicle's Monitors have run and completed their diagnosis and testing, and which ones have not yet run and completed testing and diagnosis of their designated sections of the vehicle's emissions system....When a vehicle first comes from the factory, all Monitors indicate a “HAVE RUN” status..
Before an Emissions Test (Smog Check) can be performed...some areas also require that all the Monitors that a particular vehicle supports indicate a "Has Run" status condition before an Emissions Check may be performed....Other areas may only require that some (but not all) Monitors indicate a "Has Run" status before an Emissions Test (Smog Check) may be performed."
But it also says:
"all emissions-related components and systems are continuously or periodically monitored, tested and diagnosed whenever the vehicle is in operation."
So.. in theory the vehicle should re-run these tests automatically and re-set the status codes to "Have Run" long before my next emissions test.... or will it?
CanOBD2 - Tech+Info%2cOBD+Knowledge - I/M READINESS
"I/M Readiness shows whether the various emissions-related systems on the vehicle are operating properly and are ready for Inspection and Maintenance testing.....I/M Readiness Monitor Status shows which of the vehicle's Monitors have run and completed their diagnosis and testing, and which ones have not yet run and completed testing and diagnosis of their designated sections of the vehicle's emissions system....When a vehicle first comes from the factory, all Monitors indicate a “HAVE RUN” status..
Before an Emissions Test (Smog Check) can be performed...some areas also require that all the Monitors that a particular vehicle supports indicate a "Has Run" status condition before an Emissions Check may be performed....Other areas may only require that some (but not all) Monitors indicate a "Has Run" status before an Emissions Test (Smog Check) may be performed."
But it also says:
"all emissions-related components and systems are continuously or periodically monitored, tested and diagnosed whenever the vehicle is in operation."
So.. in theory the vehicle should re-run these tests automatically and re-set the status codes to "Have Run" long before my next emissions test.... or will it?
Postmaster
Joined: Dec 2001
Posts: 3,742
Likes: 2
From: UT
Here's what I know:
"Freeze frame data is data about the various sensors/actuators that occurs at the moment the trouble code is set. Can be useful in diagnosis to review that data and see which sensors may have been out of range at the time a DTC is set. Best thing to do before clearing would be to access the freeze frame data (if you have/can get access to a suitable scanner to read it. Of course, if the code comes back, the PCM will store another set of freeze frame data for that instance of the code.
I'm guessing this is additional "manufacturer specific freeze frame data" that is stored with each DTC, but I'm not sure. In any case, you would need a suitable scanner to read this data.
You are basically correct about the I/M readiness monitors. The only thing I will add is that it can take several "drive cycles"/miles to fully complete the testing and set all the monitors to ready (Technician who tested mine once suggested 200 miles). As long as your next emissions test isn't real soon, they should be completed and ready.
HTH
"CAUTION: Erasing the Diagnostic Trouble Codes may allow the scan tool to delete not only the codes from the vehicle's on-board computer, but also "Freeze Frame" data and manufacturer specific enhanced data. Further, the I/M Readiness Monitor Status for all vehicle monitors is reset to Not Ready or Not Complete status. Do not erase codes before the system has been checked completely by a technician."
Very ominous.
So :
- what the heck is "Freeze Frame" data and should I be worried about erasing it?
Very ominous.
So :
- what the heck is "Freeze Frame" data and should I be worried about erasing it?
- what is "manufacturer specific enhanced data" and should I be worried about erasing it?
- what is " I/M Readiness Monitor Status" and should I be worried about setting it to Not Ready or Not Complete status?
HTH
Posting Guru
Joined: Feb 2004
Posts: 1,388
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From: Saratoga, NY
Unless you have an emissions inspection coming due in the next couple weeks that requires your vehicle to be connected to an inspection machine like we do here in NY just go ahead and erase them.
200 miles to run the I/M monitors is a bit excessive, I can usually get them to run in less than 20, you just need to know what to do to make it happen.
finally, do you have any codes to clear? If so what are they?
200 miles to run the I/M monitors is a bit excessive, I can usually get them to run in less than 20, you just need to know what to do to make it happen.
finally, do you have any codes to clear? If so what are they?
Postmaster
Joined: Dec 2001
Posts: 3,742
Likes: 2
From: UT
Most likely true. At the time, I didn't have a scanner to check, and he was probably erring way on the side of caution to make sure he didn't get a "have to drive it some more and come back" scenario.
