cdsjklee

Hello. I have 04 SL55 failed smog it says MIL/Check Engine Light but I do not have any check engine lights on the car. few days bdfore the smog test it briefly showed battery warning light visit workshop right after i started car but it went away when i drive the car. I have changed consumer battery few month ago and never had the warning lights. I did the OBDII chcek and it does not have any code present. eha t might be wrong any ideas.

Thanks

_AMG_

Do you have any mods done to the exhaust? (2ndary cat delete, primary cat delete, High flow cats?)

cdsjklee

Just Brabus exhaust and resonator delete and Eurocharged tune which was done few years ago

driveability

In some stated the tech will plug in the diag connector under the dash. That will look at emission tests flags. If your battery dipped low or some other quirky thing happened to the computers voltage supply the flags would reset to something like a testing mode. Some cars need to be driven a lot to get all flags to pass internal tests. HST, if you have a issue that sets the light and just cleared it before the smog test it will fail for the above reason as well, or just disconnecting the battery will cause the car to fail ALL THOSE REASONE STATED ABOVE WITHOUT THE CHECK ENGINE LIGHT BEING ON IN THE DASH..