Upshift delay switch over valve
 

The check engine light has come on in my 1994 E320 and the cause is a faulty Upshift Delay Switch Over Valve. I have three
questions.
1. The car runs fine with no other problems. I understand that this has something to do with heating the catalytic converter in cold weather. Is this something that needs to be fixed or can I
just ignore it?
2. If it is a must fix, about how much will it cost to fix it?
3. If it is not a must fix, is there some way to turn off the check engine light?
Thank You, Bill Scott

Should be OK
 

From what I've read - there's no problem running your car without the upshift delay.

As for the CE light - I think that it will stay illuminated as long as the fault condition exists. Learning to live with it is probably the easiest answer (although it could mask true problems that the CE light should reveal).

Troy
1995 E420 81k

The fault code for a faulty upshift delay valve is #26, but it doesn't mean that the problem is the switch over valve.

It simply means that the upshift delay function is not working.

The s/o valve is cheap - less than $50, but the problem is 95% of the time a vacum leak in the switch over valve itself, which is located on the side of the transmission. This part is about $250.

You can drive your car like this with no problem, but it will not pass the smog test.

You can shut off the CE light by reviewing the codes in the DM module, then hold down the button for several seconds. However, since the upshift delay is not working, the CE will come back on in a few days.

The process for doing this has been posted many times before. Try a search.

Same problem with my '96 C280 turned out to be the vacuum lines under the plastic cover on top of the engine had cracked. Very cheap and easy to fix. Check the vacuum lines and rubber fittings first.

Dan

The most common cause is a vacuum leak, hoses on the vacuum supply check valve going to the switchover valve.

The switchover valve is mounted on the firewall behind the brake master cylinder.

It has a black wire going to it (electrical) and a green hose (vacum).

You can apply vacum to the green line to see if the upshift delay valve holds vacum. If it doesn't, it's either the line or the valve itself.

Delay shift basics........

The delay system is simply an ACTUATOR on the side of the trans that , when vac is supplied to its ELEMENT, mechanically changes the position of the shift cable . [ comparable to the driver moving the gear selector to a lower gear selection]
This part of the system is not a Switch Over Valve or any other type of valve. It is a vac activated cable servo.
The activation of this cable actuator is controlled by the ECU sending an electrical sig to the SWITCH-OVER VALVE as determined by the ECU mapping. This allows engine vac flow to reach the tranny cable actuator through the SOV. [ this is the part behind the booster and is just an open/closed electrically energized valve]
As soon as the ECU is satisfied , it stops the signal to the SOV ,which then closes and vac flow ceases to the actuator, allowing the cable to return to normal shift position.

So, a code 26 can be anything from no electric sig to the SOV to a bad actuator...and anything in between. [vac hose leaks,etc]
An easy test is to take the 2 vac lines at the SOV off and connected them together with a small piece of tubing. This eliminates any ECU engine management of the delay system. Take the car for a ride and see if the actuator is responding to engine vac.
[the tranny should stay in delay mode] Check for engine vac at the disconnected line before putting them together to assure of vac at sov in-line from engine]
This simple test gets vac right to the cable actuator and you can work back from there..if you now have delay , then look at SOV flow and ECU signal to SOV, etc. If not , you have bad element in actuator, bad actuator, or [ and don't overlook this ] a broken vac line at actuator.......
Many guys just put a BB in the line at the SOV and use a lower shift range when the car is warming up [ serving the same system purpose]. But, then the CE comes on and has to be erased. [ surpisingly, sometimes this can take a month]
The reason for the BB line plug is to prevent a vac leak while the SOV is open.....

Please help
 

//
Would you please continue on this topic. I have these simptoms on my 95 e320 s/w, code 26.
I applied vacuum on the green tube leaving the s/o/ valve but it doesn't hold vacum.
The problem is that I just can't access the actuator to do any more testing. It is so tight, I think the transmission has to be removed to gain access to the unit. Can you give som instructions, please?
Many thanks,
Frank

BillScott, I recently had mine fixed. You can drive it but the vacuum leak, if that is what it is, will cause the transmission to shift differently than what you are used to over a period of time. Mine wouldn't kick down to 3rd on the highway as fast as it used to. Now it shifts like a race car.

Arthur Daltons' explanation is right on the money. In regard to how long it takes for the CE light to come back on, a few things must be considered. First, DM is looking for a certain RPM/vehicle speed to be reached. This is how it knows the upshift has actually been delayed. Next, the upshift delay isn't needed unless the engine is stone cold. If you were to start the car and let it warm up for a few minutes, DM wouldn't even run the test. Next, the engine load must be below approx. 50%. If you drive with a heavy foot immediately after start-up the test isn't run. Finally, the self-test must fail on two consecutive "trips" or "drive cycles". A code will be stored after the first failure but the CE light won't come on unless it fails twice in a row. I hope this helps.

I am experiencing minor flare between 2nd and 3rd gear upshifts. Tech looked at car, and I believe he checked/tested vacuum at the SOV. Diagnosis was:

"Shift Point Cable" leak in vacuum element on the transmission.
Cost of repair: $1,200 parts and labor

I declined the repair because it is a non-critical issue. The Tech capped off the vacuum line to the tranny, to stop the vacuum leak, and installed a new shifter bushing (at my request). Net cost: $51.00

Presently, shifting is near-normal, with a minor 2-3 flare. To confirm the vacuum leak diagnosis, I checked the DM for a code 26, but got only my ever-present Code 5 (because I have an EGR tube to clean). I did, however, see a code 26 back in November, which never returned after I cleared it. Questions:

1. Is the above diagnosis by the tech reliable? Can the leaky vacuum element, alone, be replaced, versus the entire "Shift Point Cable?"

2. Before even considering replacing the vacuum element, would it not be wise to first test the vacuum line from between the SOV and the trans element, since that is what could be actually leaking?

3. With no vacuum to the transmission element, will my 2-3 upshift delay/flare persist?

4. Can tweaking the throttle cable, Bowden cable, and Vacuum modulator compensate for, or eliminate, the upshift delay?

So far, I have experimented with the Throttle cable, mistakenly thinking it was the Bowden cable. Tightening it did speed up the timing of the shifts, helping to mask the flare. But it also made me go faster than I should with normal accelerator peddle pressure, so I restored it (almost) back to its original position.

Other than that, I have located what I believe to be the Bowden cable (see photo); and identified the vacuum modulator on the trans. (I have the newer-style white plastic cap.)

Thanks for any advice.

If it's the vacuum modulator that needs to be replaced, it's no big deal. $70.00 CDN list price. I installed mine after asking much the same questions here about accessibility. You have to remove the rear transmission mount, and then push a block(s) of wood between the transmission and the tunnel on the driver’s side. This moves the tranny over enough to unbolt the modulator and replace. This would be tricky on your back but it was easy on the hoist.

John

John, thanks for your reply.

The Vacuum Modulator -- on the driver's side -- is OK. It is the vaccum control valve on the passenger side of the transmission that is allegedly leaking. Is that the one you replaced?

Check Engine Light
 

I had the same problemwith my 94 SL500. I took my car to the local MB dealership in Columbus and the ran a test and it was again the Upshift Delay Valve (about $275.00 in parts and 4 1/2 hrs labor at $110.00/hr). My mechanic said that it reads the catylic converter heating up. Again, he told me like all othres that it is just fine to run the car without replacing this valve. He cleared the codes and so far the Check Engine light has not came back on. Only has been a few days though.

Roger Gray
128,700 miles