Check Engine Light but not Codes per Tech
 

Help needed ASAP Please.

1994 E320

Symptom: Check engine light on, and trans is not delaying the shift when cold (it should)

I previously pulled the code 26 (shift delay fault). The shift delay valve near the master cylinder holds 15 in of mercury. The shift delay unit on the trans hold only 5 in. mercury. I would have replaced this if I could, but not sure if this is the issue, So I took it to a shop yesterday.

Shop used a Bosch code puller (or what every you call it) to communicate with the vehicle.

NO CODES WERE PRESENT. But the check engine light is on.

Shop is talking about replacing the ECM (Engine control module). They stated it may be an issue with it, they are not sure of course. It cost about $1 and they can not ensure that it's the problem.

What could be the issue. I do not think the ECM is bad. Any advise????


HELLLLLLLP...............

John

<<Shop is talking about replacing the ECM (Engine control module). They stated it may be an issue with it, they are not sure of course. It cost about $1 and they can not ensure that it's the problem.>>

For that kinda deal, have them change it and get me a couple of extras >>>
Kidding on your typo, but that would be nice, wouldn't it ??


If you have a CE , you have a code
You can go get that code yourself from under the hood with the push button led/sw..
ch search and the procedure will be there
You may have others besides the 26..

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.

For primary diagnosis, it is quite easy for the DIYer to isolate the vac/mechanical side of the system from the electrical without gauges and pumps, etc...
Simply unplug the green plastic line at the SOV from its rubber hose . Now unplug the rubber vac line on top of the SOV.
You can now insert the plastic green line into the bubber SOV feed line you just disconnected..
This eliminates both the SOV and the electrical system circuit.

Next morning, cold car, go down the road and see if you have delay...
If you do , you problem is electrical [ signal feed to SOV]
If you don't , you have a vac/element/actuator problem...
As soon as this test is done , simply pull over and plug the lines back in the original nipples/hose....

This save much time/thought as it gets you immediately to the fault side of the system for further testing..
After this test , I would then verify the SOV operation as the next step w/manual voltage source.....

Haha ya, only $ 1. I forgot the k, it's 1k for a ECM.

I told the tech, it's not the ECM, it may be the shift delay valve on the trans. I checked previouly the shift delay and the unit on the trans. I told the tech this, now he agrees, it's not the ECM.

The tech recommends that I just plug the vac line going to the shift delay switch on the trans and forget about it. Will this stop the check engine light from coming on?

Code 26 is the only code present. From this excellent site, I pulled the code and determined it may be the S/o valve.

It looks like the trans has to be dropped to change the unit on the trans. Correct?

<<The tech recommends that I just plug the vac line going to the shift delay switch on the trans and forget about it. Will this stop the check engine light from coming on?>>

Unfortunately, No.. the CE is computer tripped when the diagnostic mapping test looks at rpm signal..
Many put a BB in the line . [ me included] and once in a while check the code situation.. easy to clear on that DM..
It is one of the feature that tech/owners hate .. I personally use 3rd gear position til my cars are up to temp... so this helps the cat along with keeping my driving preference..

<<Code 26 is the only code present. From this excellent site, I pulled the code and determined it may be the S/o valve.>>

The cod 26 list the SOV valve , but in reality , the code can be
triggered by any part/fault of the system.. the later OBD2 systems can check codes for sov voltages and open coils , but
not on this [OBD1] system.. A code 26 should just read 'Fault in Delay System'...
Many see the code and change the SOV only to find the the fault
reoccur...
Testing of the sov is to get power to it and , while at idle, feel for vac at the outlet port [ hose connection at green trans feed line ] with tranny line disconnected.. this will verify the valve is opening and allowing vac flow....if you put a momentary sw in the power test line , you can rapidly turn the valve on/off and verify if it sticks open/closed... it should shut down solid every time and completely stop vac flow when de-energized...

I'll say it again, it still could be any part in the system.

While I'll admit that my problem was rare, the part that prevented my upshift delay system from working was the transmission safety switch.