On your 1994 E320, the upshift delay valve delays the 2 to 3 shift when cold.

It keeps the car in 2nd gear longer so that they catalytic converter warms up faster to reduce smog emissions.

There is an electrically actuated switch over valve that is mounted on the firewall behind the brake master cylinder, but I believe that 95% of the time, a code 26 is caused by the upshift delay valve malfunctioning because it no longer holds vacum.

The test is to pull the green vacum tube from the s/o valve, and apply a vacum. If the pressure immediately drops, then the valve itself is bad. It is located on the side of the transmission, and costs about $250.

If it holds vacum, then the problem is the s/o valve and it is a less than $50 part.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".