I think WD40 breaks down rubber. I'd try Marvel Mystery oil, possibly.
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Upshift Delay Switchover Valve, Open/Short Circuit (DM Code 26)
- Thread starter emerydc8
- Start date
I think WD40 breaks down rubber. I'd try Marvel Mystery oil, possibly.
Just the other day I was looking at the vac hoses behind the brake booster and the yellow check valves and I found one of the valves was shot and a almost completely severed elbow. I replaced both and the code 26 is gone. During a cold morning I get a very distinct upshift delay that I did not get before. I tested the vac lines to the valve behind the brake booster that Dave and Gerry were talking about and it checked out. Also it turned out the PO replaced the vac actuator at the side of the trans which held vacuum too.
When I connected everything the system - no more codes. I used to get them every week after I cleared them - for obvious reasons.
Now I am moving off to my frustrating drivability issues.
When I connected everything the system - no more codes. I used to get them every week after I cleared them - for obvious reasons.
Now I am moving off to my frustrating drivability issues.
I have the component behind the brake booster capped as well as plugging the hose going to the transmission and I'm still getting a DTC 26 (upshift delay) on the Diagnostic Module. Do I also need to unplug the wiring to the solenoid too? Should I jumper it to keep the code from appearing? 
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Hey Jon,
The capped hose, isn't that the one that comes directly from the intake? I'd vacuum text it. Also if the capped valve is bad I don't remember it being expensive to replace. The important component in my case was the line to the trans actuator. It was not getting vacuum due to broken elbow. But I tested the hose going Into it and it held vacuum. So in your case just test that hose going into the trans actuator and if that's the problem capping will not solve ur problem it seems because the vav leak may be at the trans.
The capped hose, isn't that the one that comes directly from the intake? I'd vacuum text it. Also if the capped valve is bad I don't remember it being expensive to replace. The important component in my case was the line to the trans actuator. It was not getting vacuum due to broken elbow. But I tested the hose going Into it and it held vacuum. So in your case just test that hose going into the trans actuator and if that's the problem capping will not solve ur problem it seems because the vav leak may be at the trans.
It appears that the engine management systems "watch" for the upshift delay to actually occur, based on engine RPM & temperature, etc. So if the system is disabled by disconnecting/plugging the vacuum lines, eventually a code 26 will appear. The factory docs do not state this, they make it sound like code 26 only checks for the presence of the solenoid coil resistance, but apparently it does more.I have the component behind the brake booster capped as well as plugging the hose going to the transmission and I'm still getting a DTC 26 (upshift delay) on the Diagnostic Module. Do I also need to unplug the wiring to the solenoid too? Should I jumper it to keep the code from appearing?
On my old black E420 that I sold to a friend, I had plugged the vac line shortly before selling it, and after he bought it DM code 26 would appear consistently after a week or three. So, about a month ago we re-connected the vacuum lines and enabled the upshift delay system again. After a few months we'll see if the code has not returned, if so, that will validate that GVZ was correct. Stay tooned.
UPDATE: Months later, still no code. Seems Herr Honcho was indeed correct, and the factory docs are misleading at best.
YOINK!!!
Since I replaced the cracked vacuum elbow at the end of January, I have not had any sort of check engine code return on my wife's E320 wagon, despite some cold weather (which was usually the trigger for these code 26s to appear). I am pretty close to believing that this issue was fixed with the replacement of the rubber vac elbow.
Ivan, the capped black line goes to the transmission. The other line, off the intake manifold, is white. I am pretty sure my leak is coming from the transmission side because I'm not able to pull any vacuum on that line. Next time I'm under there, I'll check to see if the line or connection to the transmission side is bad.
Dave, I guess I will just live with the DTC 26. It's not likely to happen here again until this winter. Let us know if it pops up on your friend's E420. I knew I should have bought that from you when I had the chance.
Dave, I guess I will just live with the DTC 26. It's not likely to happen here again until this winter. Let us know if it pops up on your friend's E420. I knew I should have bought that from you when I had the chance.
Nice work, guys! Please report back in a few months and let us know if the dreaded CEL Code 26 has been exorcised via BB or hose replacement.
Note that the E320 wagon has a completely different (HFM) engine management system and CEL code 26 mayr, or may not, have identical root causes compared to the .034/.036 LH system.
I have not, since replacing the rubber vac elbow attaching to my Upshift delay solenoid, experienced another code relating to this system ... particularly the DM (Dave Mushroom) Code 26 Upshift Delay code. Or any CEL whatsoever.
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It seems like there should be a way to defeat the cold shift. I've noticed since the weather cooled it takes longer for the shifting to return to what I consider normal. During summer I could let the car warm up for a few minutes and the car would shift normally, now it takes a several miles of driving to reach nirvana.
Re: cold shift defeat
The golf tee is used to plug off the vacuum line controlling the upshift delay function. Further discussion here.
The golf tee is used to plug off the vacuum line controlling the upshift delay function. Further discussion here.
Gerry - Did the code 26 ever came back?
No, it never did, but I sold the car in 2015. I have gotten this code recently on my E500, and I cleared it and am seeing if it is going to come back on that car. Which reminds me, I should go and check to see whether it has come back.
I get the same two codes. Will be interested to see what you find.
Cleared the code today and also did a visual inspection around the green tube by the firewall but did not see any cuts. Will see Code 26 comes back.
Regarding Code 4, it pops up every 3-4 months but haven't looked into the air pump yet.
Looks like Trae had similar issue with M104 on his Cabrio but haven't seen an update on this thread:
https://500eboard.co/forums/index.php?threads/im-over-my-head.2413/page-2#post-32451
Thank you Gerry and GSXR. I went to Canadian Tire and picked up some BB's ($4.00) and then came back to test the vacuum. Sure enough, line held vacuum but the rubber elbow was shot. Thank you guys, saved me a lot of headache...Now what to do with these BB's?This thread prompted me to go outside and test my E500 and my E320 wagon using the Mityvac test, as it has been some time since I've done this.
The E500 has never given me an upshift delay code. The E320 has given them to me for at least the past 3-4 winters.
The E500 tested just fine. You can see the solenoid (switchover valve) behind the booster here, and then the attachment of the Mityvac, and steady reading of the Mityvac.
View attachment 12945View attachment 12946View attachment 12947View attachment 12948
Next up was the E320. You can see that the E320 has a green vacuum line, as opposed to the black-with-green-stripe line of the E500.
View attachment 12938View attachment 12939
Then, I disconnected the rubber elbow from the switchover valve, and attached the Mityvac. No vacuum. None.
View attachment 12940View attachment 12941
Pulling the Mityvac off of the rubber elbow, I found the following:
View attachment 12942View attachment 12943
Replacing the rubber elbow with one from my stash (remembering the extra 124 elbows I had from replacing them at the ACC vacuum distribution point behind the passenger side airbag) it was a 30-second operation to replace the elbow and re-attach the Mityvac.
Voila! We have steady vacuum.
View attachment 12949View attachment 12944
So, it seems that my wife's E320 code 26 may well be caused by a faulty rubber elbow at the connection of the vacuum line between the switchover valve and the transmission's upshift delay valve. We'll see if a code 26 returns.....
In the meantime I'll order the correct vac elbow on my pending MB parts order.
Thanks, GSXR, for prompting me to go out and check my cars !!
Cheers,
Gerry
