On my '94 E320 wagon, I periodically get a check engine light with codes 5 and 26 at hot start-up. The check engine light only comes on and stays on when I start the car hot, never when cold. And if it doesn't come on at start-up it won't come on later while the engine is running. Also, it only comes on if I turn the key very rapidly from off to on. It doesn't illuminate if I turn the key slowly (except for the bulb check sequence).
I have replaced the key switch and the overvoltage protection relay at the advice of my mechanic, but no improvement.
Suggestions?