C280- 1996( in-line 6) CAN NOT PASS SMOG TEST. Fully serviced by independent Mercedes shop, in excellent condition, no engine light ON, battery was disconnected. Upon reconnecting battery some sensors do not report to smog test station during test. Tried driving recommended test profiles with hope sensors will "come back to life" but to no avail. Dealer wants to perform 3 hour diagnostic test for $280.00+. Any advise will help.

 

what is smog test... the exhaust gas?

 

It is basically a test done to make sure the test can be driven on public roads or not.
Besides the exhaust gas you mentioned, a vehicle can fail the test if the check engine light comes on.

 

that is a very strict regulation.

that means they attached some scanning computers to read the value of sensors too? but the lambda sensor takes sometime to go into close and open loop mode.

in here, you just bring a ream of cigarette for the testers and... you passed the test.

 

Seems odd that they'd rely on the car's sensors instead of using their own. After all, you can buy or make simulated sensors that output whatever you want them to output. That's especially true of the O2 sensors which they would be most interested in (I guess?). Whatever happens before the exhaust tip doesn't really matter, does it? If it stinks, it stinks. If it don't, it don't.

Also, each state chooses how they do these tests, from how often it's done to what is checked and what values are pass and fail. I realize you guys are probably talking about California exclusively.

 

it can easily be simulated.

i got one S320 customer once who complaints that he didn't pass the government inspection test. i found out that the control unit was not set to the right version and program it. (says non KAT, so i set it to KAT)

he went back there for the test after 20 minutes and the CO reading was 0.05, when just a few moments ago it was so high. the idiots take out another gas analyzer thinking that their equipment was broken. the same results, almost no CO reading! they take out the spare gas analyzer, and decided they got problem with their equipments!

what they didn't know was that i have set the CO to the leanest point.

 

They must check the relevant sensors on the car just to make sure they are working, but use their sensors for the actual stink test from the exhaust ... or something.