MIL Check Engine Lamp

[B52]

On my 1998 MBZ 320 ML, the wife left the gas cap off, drove the car, and now I have the MIL light on showing the dash. How can I reset the computer without a 60 mile trip to the dealer?

[DR.DIESEL]

Tighten the gas cap and drive. If thats all it was, the MIL will
turn off most likely after a day of driving or so.
The fuel inj system needs to conduct a test to check for a leak
in the tank. The car needs to be run for a min of 30 min to
get this done.
Happy driving.
DR.D

[ke6dcj]

Do a "google" seach for "OBDII drive sequence". If the gas cap is properly sealed, and you do the drive sequence, it should reset itself.

:-) neil

[B52]

It worked. Light is out. THANKS!

[slsmag]

Originally posted by ke6dcj
Do a "google" seach for "OBDII drive sequence".

>>Your search - "OBDII drive sequence" - did not match any documents. <<

Neil - can you elaborate... or point to source on the web?

- michael

[ke6dcj]

Sometimes you have to be a little more diligent in your searches:

RUNNING AN OBDII DRIVE CYCLE

Suppose you’ve "fixed" an emissions problem on an OBDII-equipped vehicle. How can you check your work? By performing what’s called an "OBDII drive cycle."

The purpose of the OBDII drive cycle is to run all of the onboard diagnostics. The drive cycle shold be performed after you’ve erased any trouble codes from the PCM’s memory, or after
the battery has been disconnected. Running through the drive cycle sets all the system status "flags" so that subsequent faults can be detected.

The OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another).

NOTE: The ignition key must not be on prior to the cold start otherwise the heated oxygen sensor diagnostic may not run.

1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear defrost on. OBDII checks oxygen sensor heater circuits, air pump
and EVAP purge.

2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. OBDII checks for ignition misfire, fuel trim and canister purge.

3. Hold at a steady state speed of 55 mph for three minutes.

OBDII monitors EGR, air pump, O2 sensors and canister purge.

4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. OBDII checks EGR and purge functions.

5. Accelerate back to 55 to 60 mph at ¾ throttle. OBDII checks misfire, fuel trim and purge again.

6. Hold at a steady speed of 55 to 60 mph for five minutes.

OBDII monitors catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors and purge functions.

7. Decelerate (coast down) to a stop without braking. OBDII makes a final check of EGR and canister purge.

[B52]

So now I need a smog check. Will the OBD computer have this gas cap failure saved in the memory? If so, will the car now fail the smog test because of a failure saved in memory?
Should I disconnect the battery to erase the memory?

[slsmag]

Thanks Neil, for the detailed info - it's very helpful.

- michael

[B52]

Well - it passed the smog check. FYI - under smog check II in California, they do not check the computer for failures saved in computer memory - they only check to see that the lamp is functioning and that it is not on while the engine is running.
Thanks for the Help

[wjm]

Man. I need to find a back road somewhere where I can drive 55 then 20 then 55. Thanks for the info, but the engineer who came up with this method must have been on something! :-)