My 2004.5 volvo s40 had check engine light on weeks ago. Then the dealer replaced the oiltrap but the light was still on. Two days later, the light was off itself with no reason. I sent it to the shop to check the buzzing brake vacuum pump. After the technician moved the pump away and put it back, the check engine light was on again and the information center showed engine service required. The codes were ECM 531d and 900e. Yet the amazing thing was that after the technician scanned the car and turned it on again, the light was off and did not come back until now. Should I send it to the dealer's shop to check the problem again? Or just discard it since the light does not show up any more? Thanks a lot!

 

Hmm... I would say if it comes back on, yes. Those codes seem to be internal faults in a module, which is not good.

Has this vehicle has A-pillar connectors installed? any window, lock, a/c problem intermittent?