I was recently given the privilege, unwilling, to start shopping for a replacement used car for commuting to work. I have always had my trusty scan tool with me when looking at used cars. A family member loaned me their much nicer scan tool to use this go around. Not only does it read codes and all the normal stuff. You can also dig a bit deeper with it and perform a module scan of the car.
The last four cars I have gone and looked at looked promising. Relatively low mileage Honda's with 1 owner. No check engine lights or other trouble lights on dash (I did verify they turned on before starting car). Additionally no codes when throwing the scanner on it.
A rereHowever, when I performed a "module scan" of the vehicle they show a number of stored "permanent dtcs" . From my understanding permanent dtcs are emissions related so you can't cheat on emissions regulations. However, these stored codes were for things ranging from the ABS system, electronic power steering, and the SRS system. Nothing about emissions. Some of them were rather serious sounding like airbag deployment.
My question is, what are these codes? I can't seem to find much on a Google search for what these codes indicate. If I hadn't done the module scan, I would have never known about the "issues" and possibly purchased the car. Are these truly codes I need to be concerned about or ignore them? If they are indications of a real problem with the car, why would the car not have actual codes and dash lights turned on?
nope. Stored DTCs can be anything
Permanent Diagnostic Trouble Code (DTC) is stored when a DTC is confirmed and the Malfunction
Indicator Lamp (MIL) has been illuminated. A Permanent DTC can only then be cleared by the module
strategy and cannot be erased by clearing DTCs with a scan tool, a Keep-Alive Memory (KAM) reset, or
battery disconnect. Permanent DTCs will be displayed on Integrated Diagnostic System (IDS) beginning
with release R104.
The intended use of the Permanent DTC is to prevent vehicles from passing an in-use inspection simply
by disconnecting the battery or clearing DTCs with a scan tool prior to the inspection.
A Permanent DTC will be erased one of two ways:
After three consecutive confirmed fault-free monitoring cycles. The MIL is extinguished and the
Permanent DTC is cleared at the start of the fourth fault-free monitoring cycle.
After one confirmed fault-free monitoring cycle following a scan tool “clear DTC” request.
A driving cycle must include the following:
The OBD monitor must run and determine that that fault is no longer present.
Cumulative time since engine start (or propulsion system active for hybrid vehicles) is greater than 10
minutes.
Cumulative vehicle operation above 40 km/h (25 MPH) occurs for greater than 5 minutes.
Continuous operation at idle (i.e., accelerator pedal released by driver and vehicle speed less than 1
km/h or 1 MPH) for greater than 30 seconds.
First off, thanks for the detailed reply, that was very helpful and informative. So based on your response, if I am showing permanent DTCs on a car but no MILs are illuminated, I don't know for certain if their is a problem. I would need to perform the steps you outlined above in order to see if the codes go away before determining if the codes are still present or not?
I think of them more as a log file. Example if the air bag was replaced then the light will be off, but you have a record of it’s deployment, so you know the car at some point had a collision serious enough to deploy the airbags.
I will add, even on the airbag ones, they will eventually clear.
So to give a real world example, I looked at a civic last night that had a bunch of SRS and ABS codes that pulled up when I did the full module scan. No codes when doing the normal scan. No MILs illuminated either.
Here are the ABS codes for reference.
ABS 61-1 Modulator-control Unit Initial IG Low Voltage
ABS 81-32 Central processing unit internal circuit malfunction
ABS 54-21 Fail-safe relay 1 stuck off (main)
ABS 61-21 Modulator-control unit power source lower voltage
SRS codes:
SRS F1-11 left front airbag and/or left front seat belt tensioner deployed
SRS E1-11 left front airbag and left front seat belt tensioner stopped deployment
My big question is, if the computer is recognizing these as potential issues and stored them as DTCs, why wouldn't the MIL illuminate to show an issue that needs to be resolved.
The issue may have been resolved. New Air bag installed. Think of Perm DTC’s more as a log file