W126 kickdown switch woes...

[Hit Man X]

Hello all..

I've tried three kickdown switches in my SDL to no avail, I still do not receive 4-3 kickdown. Is the wiring fused somewhere I do not know about? Do I need to have a working tach for it to operate? I feel like I'm missing something silly here.

Thanks.

[bhatt]

The tach working or not shouldn't make a difference.

Have you checked to make SURE the drivers floormat isn't covering the kickdown switch? It slides over and covers the switch, resulting in no kickdown.

Mine stopped working a few years ago and it turned out to be a relay related to the HVAC system. Apparently the kickdown circuit is powered from the AC unit somehow, since the compressor shuts off while in kickdown (to ensure max engine power). It turned out to be the KLIMA relay and it is located between the two firewalls. If you know where the OVP relay is on your car, it's right next to it.

Neal

[Hit Man X]

Oh yes, that was the first thing I checked. Then swapped out many different switches, reversed the wiring, etc.

Interesting regarding the Klima relay, I'll have to snatch one a few this week and try that. It'd be nice to have that working.

[bhatt]

That narrows it down considerably, now that you've tested the switch and ensured the mat isn't blocking it.

I am going from memory here, but I think the kickdown switch is a simple two-wire switch that is bridged when you floor the accelerator. One side of that circuit is powered by the Klima relay and I would guess the other side is ground. So if the klima relay goes bad, you won't have any kickdown.

I didn't have ANY symptoms of a bad relay other than the fact that the kickdown didn't work. Car ran like a dog, but that was about it. Climate control continued to function properly as far as I remember. It was the middle of winter, so I'm not sure if there was any affect on the A/C compressor (I would guess the A/C wouldn't work with a bad Klima!)

If you can get your hands on another one, try it out. It would take some work, but I can probably dig up a wiring diagram. I think if you bridge two pins where the Klima relay plugs in, you can get kickdown and this will tell you if it's the relay or not. It's MUCH easier to just swap a relay if you have that opportunity!

Let me know if you need the wiring diagram.. I'm hoping a new Klima fixes everything for you.

Neal

[bhatt]

I just did a quick search and found the info that helped me fix mine.. sounds VERY similar to the problem you're having and the steps you've already followed.

By the way, I believe Dr. Booth is a member of this forum also. He tends to know his stuff REALLY well!

QUESTION:
Date: Tue, 24 Jul 2001 08:44:53 -0500
From: "John Winn"
Subject: [DIESEL] 1987 300SDL trans kickdown problem..

Hello group,
I have had this intermittent problem since I bought this car and yesterday
replaced the kickdown switch on the floor, thought it fixed it but this
morning back to not working..The transmission kickdown would only work
intermittently. When it would decide to work it worked great..I figured the
first thing I would try was a new switch. Went from not working to working
just by popping in the switch, figured that was it..Is the only component
other than the switch the solenoid or is there some "computer box" that
controls this? I think I read somewhere that it is supposed to control the
AC compressor too. Is the solenoid on the trans something I can change
myself? I hope someone might have an idea, the car really doesn't have a
lot of low end "git up and go" without this working...Thanks in advance!!!!
John
I can't believe the transmission is not even mentioned in the repair manual
CDs...

ANSWER:
Date: Tue, 24 Jul 2001 10:40:06 -0400
From: Marshall Booth
Subject: Re: [DIESEL] 1987 300SDL trans kickdown problem..

John, HAVE you changed ALL the fuses?!!! There is NOTHING
you can do more cheaply and you have a better then 50:50
chance of correcting the problem. Fuse 7 on a W124 is the
fuse that controls it (I'll have to check on the CD for a
W126 - it's fuse 5) and there is interaction between the
KLIMA relay and the kickdown switch! The kick down switch is
powered from pin 6 on the KLIMA relay and is diagramed in
the W124 climate control compressor clutch control drawing
in the Electrical Troubleshooting Manual (I don't have a
W126 electrical manual but it can be located on Fig. 83/25a
in the W126 climate control manual on page A6). There is a
note that refers to the KLIMA/kickdown circuitry ONLY
existing in the '86 model year (these notes have not been
entirely reliable in the past, but I wouldn't entirely
discount them either). Back to the W126 CD to see if there
is a reference to the kickdown switch in the MAIN electrical
index. File ETM/126from86.pdf shows this KLIMA to kickdown
switch/solinoid circuitry for W126.125/134/135 from MY '86
through '91 but it is NOT clear what particular signal to
the KLIMA relay interrups the kickdown signal. Based on the
experience I've had with multiple W201s and a W124 (with
much of the same wiring and relay layout and essentially the
same circuitry with MINOR modifications) I would pull the
KLIMA and overvoltage protection relays and clean the pin
contacts and be sure that the female "sockets" have not lost
position within the socket attached to the chassis and that
they are FIRMLY grasping the male pins that plug into them
(if replacing fuses doesn't cure the problem). I have had
this problem intermittantly on my '87 190D 2.5 NON-turbo but
I solved it - I swapped the automatic transmission for a 5
speed manual and now don't have ANY use for a kickdown
switch ;-)

Marshall
- --
August M. Booth, Jr. Ph.D.

[C32AMG]

Part throttle kick down is control by the Bowden cable, no 4t to 3rd try making the cable
Tighter.


Full throttle kick down is control by the KD solenoid.
Fuse #5 powers the kick down solenoid thru the AC compressor control unit.
Key on check for battery voltage at the switch, black / white stripe wire, no power
Check for codes at X11

Power at wire, jump black/ white stripe wire to black wire at the switch/ pedal,
Disconnect black wire at the KD solenoid, passenger side rear of the transmission
If you have no voltage at that wire, check for a break in the wire. Voltage at wire,
KD solenoid defective or Valve body.

[Hit Man X]

Interesting, my A/C comp doesn't kick on anymore either.

[Hit Man X]

Okay, new Klima is in. A/C comp works again too.

Still no kickdown.

Would my SDL show codes at the X11 terminal? Does this solenoid go bad often?

[bhatt]

Hmm.. seems odd that the A/C would now work but not the kickdown.

Did both go dead at the same time?

Perhaps in trying to fix things, you somehow disconnected the kickdown switch? Now that you have a good Klima relay, run all the same troubleshooting tests again on the switch.

Maybe someone here can jump in and clarify, but I thought the kickdown was a simple two-prong switch. Without it working, your car will never shift down a gear. If you jumper across it and drive the car, shouldn't it stay in 1-2-3 gear only (never go into 4th?) It should act like you have it in "3" rather than "D".

Give that a shot.. see if jumpering the switch tells the car that the it is in kickdown all the time.. if so, you have a bad switch.

If not, I have no idea

Neal

[C32AMG]

Do you have voltage at the black / white stripe wire at the KD switch under the pedal? Yes the switch does go bad, but
I would verify source voltage first.

You can test with the ignition on.

Power at wire, jump black/ white stripe wire to black wire at the switch/ pedal,
Disconnect black wire at the KD solenoid, passenger side rear of the transmission
If you have no voltage at that wire, check for a break in the wire. Voltage at wire,
KD switch defective, KD solenoid defective or Valve body.


Some thing I found odd, while looking at the wiring schematic, the AC compressor module showed
the kick down relay as an integral (inside) part of the module.

[Hit Man X]

Both haven't worked since I picked up the SDL last July. I figured the A/C would as the clutch spun free, had a reman compressor, etc. So it works now, just seems low on R12.

I tried a few different kickdown switches in the past to no avail. But that was prior to the proper Klima relay installed.

Once I get the cruise control stuff put back in, I'll put it out of the garage and check under the trans to see if a wire is disconnected.

[Hit Man X]

Well it was still plugged in behind the trans, I'll have to check for voltage at the unit. Hopefully it's there...

If the solenoid is bad, where can I pick up a new one from? Valve body work doesn't scare me, it just takes a while.

[brabus3.6]

Don't mean to hijack the thread but I've just found fault with my kick wire (black one) thanks to this discussion. 12V not getting through to the solenoid connector but 12V was in the wire so I clipped the wire and coldered on a new connector

[Hit Man X]

Mine was the cluster issue, the one I had in there was broken. New cluster = working kickdown.