Is it possible for a management warning light to come on and no faults be detected on a diagnostic machine? I have had a recent nightmare with my Citroen C3. The flashing MIL light came on and four unknown error messages were shown when a diagnostic test was done at local garage. They advised me to go to a Citroen dealer, as the codes were very Citroen-specific. I took a big short cut. A mate at an alternative garage reset the electrics and got the car running again. The MIL light came on again about three days later, but with no flashing light which puts the car into an almost lifeless state.

Anyway, I was put in touch with another garage to test my catalytic converter (no problems found - no charge). They did my MOT for a reduced fee - it passed. I asked them to do a diagnostic test - no faults found - no fee charged. They haven't ripped me off from the beginning so I have gone with their wisdom. Is it possible for a Citroen dealer to find error codes that other garages weren't able to find? I am driving around with the MIL light on and the car drives well, but it does feel as if I am driving along an uneven road all the time.