1996 Mercedes S420 will not reset emission monitors

1996 mercedes S420 will not reset monitors. EVAP repair was done recently due to a check engine light and the code were cleared.

There is no check engine light on at this time. I went to have a smog test and they said I failed due to monitors not being reset (readiness flags) and I need to drive the car. I had already put over 400 miles on since the codes were cleared. Over the last 7 days I drove another 300 miles and it has still not reset the 7 main monitors including EVAP, AIR, CATS, CAT HEATER AND O2S. There are no pending codes and the car drives great.

Answer:

An important Drive-Cycle parameter required to initiate the entire OBD II Drive-Cycle Test must not have yet been met.

The federally required OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F) and battery voltage above 11.5 v. Should either system sensor be defective the Drive Cycle will not run.

These are just two parameters required of all OBD II vehicles. Your 1996 Mercedes S420 may have several more specific to the manufacture. Our recommendation would be to have a local MBZ dealer or certified repair shop diagnose your vehicle's failure.

If you feel your Mercedes does not have any operational faults and would like to follow a MBZ specific drive cycle read the attached PDF below.

Mercedes Benz Drive Cycle Readiness Monitors

posted by SmogTips Support