autojava

Hi, guys:
I needs some help here for my friends 2004 C280.
This car is daily driven, without disconnecting battery or jump-start lately.
Its SMOG inspection fails because of MIL/ODB II not ready.
When I use a scanner, I find that there have two monitors not ready or
incomplete:
1): O2 sensor 2): EVAP.

Also,
1): There has no error code, (completed or pending).
2): MIL (Check Engine Light) is NOT on.
3): Five monitors (misfire, fuel, etc ) are completed.

Driving looks noraml in any condition.
Any comments? Thanks.

Glyn M Ruck

Has an O2 sensor been disturbed lately? If so you need to put on more mileage.

autojava

Hi, Glyn:
O2 Sensor is not touched manually laterly. As I remember, at last oil
change (about 8 months), I have checked the O2 wire and its
connections with flash light, without unpluged any wire.
During 06/13 - 07/04 (three weeks), the owner has travaled and thus only
drive two times. after 07/05, the car is driven daily.
Even if O2 sesor was disturbed, how EVAP monitor will be NOT ready?
Thanks.

Glyn M Ruck

Even though the EECS circuit & purge system have nothing to do with O2 sensors directly. Poor O2 sensors cycling too slowly with cold engine in open loop can cause the EVAP sensor/s to refuse to reset.

If there are no vacuum leaks & no EECS leaks/purge valve trouble, bad fuel cap then changing upstream O2 sensors will frequently get rid of EVAP not ready warnings. Sometimes a bad thermostat not allowing full operating temp can lead to no EVAP reset as can a faulty temp sensor. You should get a P0128 though.

Remember that every time you cancel codes you need to go through multiple drive cycles to reset all monitors. Some say that driving must be done with half a tank of gas. Too full or empty will not give you a reset.

We don't have mandatory SMOG testing in SA yet but this is part of getting a roadworthy for sale. What makes me mad is that no one at Benz can explain to me logically parameters under which these no reset conditions occur & this trial & error approach to achieving monitor resets.

Moviela

The engineering and software departments walk along very different paths to the production line. The softwre writers are a secretive bunch, and I am not sure they always have complete comprehension of the mechanical and electronic sensors they must interface.

Rather than write a software analoge to a closed loop servo for a wide ranging device like a HEGO sensor, they use trial and error. They sugar coat it by calling it "successive approximation." I for one can't understand why injection timing is still done from "maps" created from look-up tables. Surely there is enough computing power available today to time when injection should occur and for how long on a cylinder by cylinder basis. We have come a long way since D-Jetronic, but some of the systems are still the same like manifold pressure, and mass air flow.

Glyn M Ruck

Indeed Movie! ~ Thanks for the input. I get mad when I can't understand things & I know I'm not completely stupid.

autojava

Hi, Glyn:
The owner told me that she never use the scann tool
to erase any code (in fact, she don't know there has such tool).
She owns the car from new. Two years ago, it passed the smog test.

Do you think that the weak battery (since there have only two driving
in three weeks) will reset the monitors' status? Then from July forth, since
the weather is pretty hot every day, maybe the cold starting has not
been met. Other than above, I don't know how to explain.