Check engine light turned itself off?

[NYsNumba1man]

Reset my CEL in my 03 3.0 6 speed quattro 2 night ago. Today while driving (45 miles after reset) it turned on..... I was surprised because the last time i reset it, it didn't come back for 800 miles. I didn't have my obd2 scanner on me so i couldn't pull what codes it was for, usually its for bank 1 cat and evap. Fast forward til about an hour or 2 ago i drive 40-50 miles on the highway to meet up with some friends at a car meet. Parked my car and when i came back and started up the CEL was gone.


How does it turn itself off? why does it turn itself off? Could it just be a dirty sensor or something? I did a decent amount of spirited driving on the way home and it didn't turn back on

Thanks!

[Master]

it could be the sensor, or if both evap and cat codes come on together then I would look for an exhaust leak specially at the flex or right before the cat. usually a leak in exhaust makes a back pressure and causes the evap solenoid to get confused so the light comes on. Also it could cause a low rate of smoke go through the car which again turns on the CEL for a low rate exhaust flow.

[SlickFix]

I can assure you that this is normal behavior. My Avant has been throwing codes for both cats(P0421 & P0431) for two years now, and the CEL comes and goes. One of these years I'm going to actually try to attend to those codes.

[kewe24]

Its an Audi..it has a mind of its own

[NYsNumba1man]

it could be the sensor, or if both evap and cat codes come on together then I would look for an exhaust leak specially at the flex or right before the cat. usually a leak in exhaust makes a back pressure and causes the evap solenoid to get confused so the light comes on. Also it could cause a low rate of smoke go through the car which again turns on the CEL for a low rate exhaust flow.

This would make perfect sense...... I've noticed the right exhaust has less smoke/steam coming out of it when my car warms up and i just assumed that my cat was clogged to the point it was stopping it. Ii'll check for exhaust leaks next time my cars up in the air. I hope its something as simple as that since my inspection is due in about 2 months lol

[old guy]

How does it turn itself off? why does it turn itself off? Could it just be a dirty sensor or something? I did a decent amount of spirited driving on the way home and it didn't turn back on

Thanks!

The ECM doesn't monitor the various functions on a continuous basis. Instead it performs numerous different "test" on the functions. For example, if you are on a long downhill off throttle condition the ECM will check for the fuel cut-off. Or if you are cruising at a steady state the ECM will slightly vary the A/F ratio for a short period of time and look for the corresponding reactions from the O2 sensors. Usually if the test fails for two cycles the CEL comes on. The ECM continues to perform the same tests and monitors the outcome. If the "test" passes the next three test cycles the CEL will go back to off. There are different test cycles for the different functions but the protocol remains pretty much the same.

[NYsNumba1man]

The ECM doesn't monitor the various functions on a continuous basis. Instead it performs numerous different "test" on the functions. For example, if you are on a long downhill off throttle condition the ECM will check for the fuel cut-off. Or if you are cruising at a steady state the ECM will slightly vary the A/F ratio for a short period of time and look for the corresponding reactions from the O2 sensors. Usually if the test fails for two cycles the CEL comes on. The ECM continues to perform the same tests and monitors the outcome. If the "test" passes the next three test cycles the CEL will go back to off. There are different test cycles for the different functions but the protocol remains pretty much the same.

Thanks OG!

[diagnosticator]

Reset my CEL in my 03 3.0 6 speed quattro 2 night ago. Today while driving (45 miles after reset) it turned on..... I was surprised because the last time i reset it, it didn't come back for 800 miles. I didn't have my obd2 scanner on me so i couldn't pull what codes it was for, usually its for bank 1 cat and evap. Fast forward til about an hour or 2 ago i drive 40-50 miles on the highway to meet up with some friends at a car meet. Parked my car and when i came back and started up the CEL was gone.


How does it turn itself off? why does it turn itself off? Could it just be a dirty sensor or something? I did a decent amount of spirited driving on the way home and it didn't turn back on

Thanks!

If the condition that turned the CEL ON, is no longer present, after a few driving cycles, the ECU will cancel the CEL, however, the fault code is still stored in the ECU fault memory as a not current DTC.

[NYsNumba1man]

So would i be able to pass my inspection with that stored code yet no CEL?

[old guy]

So would i be able to pass my inspection with that stored code yet no CEL?

If the CEL has been off for a few days you should be able to pass inspection. Most states now check emissions through the OBDII port Readiness codes. As long as your readiness codes are set to "0" you will pass. This is separate from any stored codes that had previously caused a CEL. The stored codes are there to tell you what caused the CEL event and will remain there until actively cleared. Once the ECM registers several sequential "pass" tests the readiness will go back to "0".

[widgget]

Parked my car and when i came back and started up the CEL was gone.

[NYsNumba1man]

Exactly what i said hahahah

If the CEL has been off for a few days you should be able to pass inspection. Most states now check emissions through the OBDII port Readiness codes. As long as your readiness codes are set to "0" you will pass. This is separate from any stored codes that had previously caused a CEL. The stored codes are there to tell you what caused the CEL event and will remain there until actively cleared. Once the ECM registers several sequential "pass" tests the readiness will go back to "0".

i had my guy scan my ecu last night just to see what would pop up and apparently the only pending sensor is for evap but he said i had enough sensors ready pass inspection. Nyc only does a safety/visual inspection and makes sure your cars CEL isn't on. Hopefully i'll be good, put on 300 miles and no CEL.

My next question is what would cause the P0441 code?> incorrect purge flow