Mercedes A Klasse System Readiness Issue

My 2008 Mercedes A Klasse, gasoline engine, with 213743 km on the clock, is showing a persistent 'System readiness check incomplete' error. The check engine light is on, and the speedometer displays a corresponding error message. The error is stored in the error memory. I recently used an OBD2 scanner for some car diagnostics, and I suspect that might be related. I've cleared the codes, but the error returns after a short drive. I'm familiar with onboard diagnostics, but this one has me stumped. Any ideas before I start chasing ghosts in the exhaust system and potentially failing my next emissions test?

4 comment(s)

Incomplete system readiness after an OBD2 read is a classic. I’ve seen it countless times, usually with cheaper scanners. The scanner probably reset the readiness monitors. These monitors need to run and complete their self-tests before the system reports as 'ready' for an emissions test. The drive cycle for Mercedes can be quite specific. What kind of driving have you been doing since you cleared the codes? Has it been mostly short trips or longer highway runs?

Mostly short trips, stop-and-go traffic, unfortunately. What exactly is involved in a 'drive cycle', and do you know the specifics for my A Klasse? I've dealt with exhaust system issues before and prefer to diagnose this myself if possible.

The Mercedes drive cycle is a pain, to be honest. It involves a series of accelerations, decelerations, and steady-state driving at specific speeds, all while maintaining certain engine temperatures. You'll find the exact procedure online or in a repair manual, but honestly, for the sake of time and sanity, a workshop with proper diagnostics equipment is usually the best bet. They can force the readiness monitors to run. It sounds like you’ve got a good grasp of car diagnostics but this is one of those situations where specialized equipment can save a lot of headache. This sounds exactly like what happened to my brother with his car, it needed a specific procedure to reset properly.

Thanks for confirming my suspicion and for the advice. I followed your suggestion and visited a workshop. They were able to force the readiness monitors to run using their diagnostic tools. The system now reports as 'ready', and the check engine light is off. No parts needed replacing, so the total cost was 0€. Appreciate your help!

Join the discussion now: