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Old 07-16-2003, 05:07 PM
suginami suginami is offline
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
95% of the time the reason the upshift delay valve fails to work is it loses the ability to hold vacum.

Pull the vacum tube (green) at the switch over valve behind the brake master cylinder and apply vacum with a mighty vac. If it won't hold pressure, it will leak out immediately, right away, while you're watching.

If it holds pretty much constant pressure for 30 seconds or so, it is not the valve on the transmission.

You would then test to see of the switch over valve is working or not.

I suffered through this problem for 3 years, constant check engine light with a fault code of #26.

I finally gave up and left it with my mechanic for a week while he swapped out parts to see what part fixed the problem. What we did know was the switch over valve worked, and the upshift delay valve on the transmission was replaced by the dealer by the previous owner, and held pressure fine. The problem was that the sw/o valve wasn't getting the signal from the ECM to open up and send vacum to the transmission on a reliable basis.

His daughter has a 1994 E320 wagon, and the upshift delay valve works on this car, so he started swapping parts.

He hooked up a vacum gauge with a long tube so that we could see if the valve was opening up and allowing vacum to flow while driving the car when the enigne was cold.

He first swapped the ECM - no change.

He then swapped the engine air temp sensor - no change.

He then swapped the coolant temp sensor - no change.

He then swapped the transmission safety switch - and voila!, it worked.

I guess some sort of short in the transmission safety switch cause it not to work. That was about 3-4 months ago, and it has continued to work since.
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".

Last edited by suginami; 07-16-2003 at 05:15 PM.
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