Saturday, January 9, 2016

Mercedes E350 DTC's

I have a 2010 Mercedes E350 4-matic.  At about 38,000 miles the "check engine" light came on intermittently.  I scanned it with a generic OBD scan tool and the Torque app.  It returned P0496 and P1077.  It started out setting these DTC's only once in a while, about 1,000 miles apart or more but it eventually happened more often.  I subscribed to the factory documentation and searched for the Mercedes DTC definitions but the documentation did  not show these 2 DTC's at all.  The generic definition is canister purge flow high.  I inspected the related hoses and found nothing wrong.  I searched forums and found some comments that people had fixed this with a new purge solenoid.  I removed and inspected my purge solenoid and found nothing wrong.  I checked to make sure it moved freely and sealed properly.  I noticed an adjustment on the top of the solenoid that was covered with silicone sealer.  I was able to poke the correct size allen wrench into the adjustment and adjust it.  The adjustment changed how far the valve opened when energized.  I ran the screw in a turn or 2.  I made sure the purge valve would still open but at a lower flow rate.  After driving the car for a while to let the monitors run the check engine light returned but this time 2 different codes were set: P0455 and P1085.  Neither of these were covered in the Mercedes documentation either so I checked the generic definition.  Now it said gross evaporative leak.  Interesting.  The DTC's changed so I know I was on the right track.  I turned the adjustment about 1/4 turn out (CCW) and drove the car again.  The MIL went out (so far).

Missing DTC's in the service information is a big industry problem.  I had this same issue on my Jaguar XJ8L.  What often happens is the controls are flashed with newer software which changes the DTC's but the documentation does not get updated.

It is also lame that Mercedes has 2 DTC's trip at the same time for a single detected issue.

I finally fixed the issue with a new gas cap.
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