OBD II Problem, Tech Help. - PeachParts Mercedes-Benz Forum

meren · #1 03-09-2008, 01:56 PM

I have read previous posts but cant fined this problem.
When I purchased my coupe it had a week battery, ok for all components but not actually to start a car. I installed a new one and drove for about 40 miles, than tried to get it inspected and my mechanic tells me you have to many not done in your OBD II too pass inspection. Drive another 40 Miles and come back. I drove total of 140 miles on a new battery and still OBD II read only 2 done all others not done

I heard there is a very specific drive cycle that is described in ALLDATA which is designed to allow a computer to complete all the readiness monitor tests in short order. Ore drive thousands of miles in hope it will work on it's own.
Can some one post this procedure ore give me an advice from personal experience?

I drove highway, local roads etc....

TMAllison · #2 03-09-2008, 03:33 PM

Not all codes will erase themselves after the underlying problem has been fixed, nor are all codes able to be read or erased using a simple OBDii scanner.

Disconnecting the batt for 30 minutes will reset most codes that OBDii is capable of reading.

To the best of my knowledge, ~50 miles of driving will reset most adaptations for MAF, trans, etc.

stevebfl · #3 03-09-2008, 04:58 PM

He is not asking about codes. He is needing his readiness monitors to run to pass emissions testing. The test stations got used to folks clearing codes to take the test and with OBDII testing all the monitors except maybe one or two need to have been performed successfully in order to pass the emissions test. Every time you clear codes you also clear the monitor test results, so if you have an emissions test coming up the car will have to be driven till they reset pass the monitor tests.

Being in a no emissions state I have very little experience with this issue, but I know from working on the systems that many of them will not even do the test unless certaing conditions exist. The evap monitor won't run if the tank is too full or too empty EVER. It also won't run if you are above a certain altitude. The cat monitor may take hundreds of miles to run if ever on a early OBDII car. There are recommended drive cycles to get the monitor tests to run but they are critically sensitive and the criteria is more than just the drive, with altitude, road condition, fuel level, etc, etc, aslo being part of the testing criteria.

I have heard of numerous pre 2000 cars that had to get exemptions because the monitors just would not run.

ILUVMILS · #4 03-09-2008, 05:25 PM

I think were talking about "Readiness Codes" here. I'm not sure about the rest of the U.S., but in New Jersey, RC's must have been checked by the engine management system in order to pass inspection. O2 sensors, cylinder misfire, EGR, EVAP, etc. must have been checked, and found to be in working order. If fault codes are cleared, or the battery is disconnected, the process starts over. If a Motor Vehicle agency finds that the RC's have not been checked, the car fails inspection. This is done so that somebody can't simply clear fault codes without fixing the problem (check engine light) in order to pass inspection.

Now back to meren's question. Like your mechanic say's, the car needs to be driven under a variety of conditions. For example, mis-fire detection and O2 sensors are monitored continuously, so they're typically the first ones to "Pass".

EVAP operation is checked once per key cycle, when the vehicle is stopped, and the fuel tank is between about 1/4 and 3/4. The EVAP self-test takes place after the engine has been running for about 15-20 minutes. If the vehicle is moving after this time has elapsed, the self-test begins when the car stops. It only takes a few seconds to run this test, but if the vehicle starts moving before it's completed, the test is aborted. The key must be cycled for the test to start again. EVAP faults (loose gas cap) are among the most mis-understood, even by some professionals.

The EGR system is checked when the vehicle is moving, above a certain speed and RPM, while decelerating. On gasoline powered vehicles, this is one of the tougher RC's to pass, IMHO. MB diesels monitor EGR continuously, so they usually pass the readiness test quickly, compared to gasser's.

Keep driving the car. It may take a few hundred miles, but eventually all the systems will perform their respective tests. Whatever you do, don't disconnect the battery !!!

pmizell · #5 07-24-2008, 08:39 PM

Living in an emissions county, I've been reading up on the testing procedure prior to driving my car to the testing shop. I have 2 systems incomplete and 7 ready which would pass me here in TX but I also have a pending code that won't go away (P0450 - fuel pressure sensor).

I found a helpful chart on the TX DOT website of what constitutes a "drive cycle" -- if you can follow a space shuttle checklist you can probably follow this. Just make sure you have plenty of road and it's 3am with no cars on the road.