Right ..which is why some can take weeks ..depending on the drivers style.

Here is a drive cycle criteria for self test verifications.

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 æ 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.


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A Dalton

Bumping this post. I've been failing smog for years due to "monitors not ready". In California (before 2011) I had to take the car to the state referee and they would override and give me the smog cert. And that was with 3 monitors not ready (EGR, secondary air sys, and catalyst).

Now the max is 2 monitors not ready. I'm going to try the above cycle and hope I get one of them going. I have an OBDII scan tool to check. Hopefully I get one of them running before my $165 diagnostic appt at the dealership on Thursday.

Finally what part of the cycle gets the secondary air sys monitor to run?

Thanks!

You'll see I have the same situation with the same readiness monitors. You'll see my threads regarding the problem but it's still unsolved after over a year. What I've noticed for sure is that my secondary air runs fine at cold startup and there is no blockage. However, the check for the secondary air, which occurs by running the secondary air momentarily at the first idle after the car has entered closed loop, does not run. I have not gotten any input from anyone as to why that won't run. I'm not focusing on the catalyst monitor as I believe that will only run after the secondary and egr monitors run. What I don't know is if the egr monitor needs to run before the 2ndary air monitor. My guess is that it should not. As I have access to another c280 (1994), it runs the 2ndary test at the very first idle after warmup every time. Please let me know if you have any success. My dealer and independent were not able to determine the problem.

I also believe the specificity of the drive cycle is not applicable in our situation. My monitors set in the past easily and without all of the drama of these specific drive cycles. I just tried to drive in varying situations, and it worked. There would have to be a reason as to why it would have gotten more difficult if not impossible to get readiness on these. 2ndary air monitor test is simply, car enters closed loop (warmed up) and then runs the pump to see that the 02 reads lean. I'm thinking wiring/CAN or ECU. Starting in 96, you can't simply swap ECUs as they're VIN Coded. Supposedly for theft protection. Sure, someone's going to just steal the ECU and not the whole car. I've switched out the Diagnostic Module as that is not coded and that appears not to be the problem as in another car, my diagnostic module works fine.

Well I attempted the drive cycle shortly after my last post. I had the front O2 sensor replaced the day before. After driving 55mph for 5 minutes and decelerating to 0 without braking, the MIL lamp comes on! This time its the rear O2 sensor. Just had that replaced yesterday. 60miles so far, no luck on the monitors.

Update: Finally took my 96 c280 to the dealership. They determined a new DM was required, costing 1780.00 (parts/labor) and ordered from Germany. The next day, they called me saying they found a used one that installed brought the priced to around 600.00. They installed the used DM and have driven the car for 2 weeks (200miles) and the same 3 monitors are not running. Now they want to order the new DM but I'm reluctant because I'll be out 1780.00 if this doesn't work. They are going to make some calls to see if its some other underlying problem before ordering the new DM.

I see you're on the Benzworld forum, as well. I responded there to your last e-mail there. I'll just cut and paste: If anything, find out how much the ECU costs as that is the one thing I can't test.

That's misinformation. The diagnostic module is not married to the car. The ECU's starting in 1996 were. I know this because I have access to a 1994 C280. I switched out the diagnostic module as the dealer said they thought it was the diag module. Must be their default answer. Anyways, I switched out the diag modules between the 2 cars and the 94 ran all the monitors (with my diag module) while mine ran into the same 3 not completing with the 94 diag module. I also know from technical sources, that it was the ECU's that were coded starting in 1996. Sure enough the 94 ECU in my 96 would not allow the car to start. It may be the ECU but I'm not going to spend several thousand on a module that can't be returned or resold. After 5 starts, a new ECU gets married to the car (really the ECU to the starter module, so if you find the pair I suppose from the junkyard, you could test it.) All I know for sure is, that the secondary air is not running the second time. Does your secondary air run after the car has warmed up? I'm sure MB has a regional technician that knows the in and outs of the OBDII crap they designed. I'm pretty sure I know more than the dealer techs at this point. I know I don't have all the tools, as well. Please keep me updated.