hillpc

Car given to me because of tranny problems ("couldn't get it into first gear", whatever that means). Finally got the engine started and running after sitting for 4 years. Drove it around the block, a little over 3 miles. From what I've read so far, I gather it's in limp home mode/3rd gear, since the engine rpm's rev high until I get rolling and then it seems to pull somewhat normally. All the PRND432 lit up. I gather that at the very least the multifunction switch that tells the computer what gear the selector is in has a problem. The strange thing is that the gear selector was bound up and very difficult to move back to Park after the drive around the block. It seemed to be free to move when first started. I did this twice with similar results. Does the selector cable manually work something in the valve body, which could be binding when warmed up? I haven't looked at the multifunction switch yet; seems implausible that it could bind up the selector handle, but only after a drive. I also haven't pulled off the selector trim to look down in there yet. (Acorns, from another post!) The car did sit for years. Also haven't listened for clicking of the brake switch-operated solenoid that locks it in park yet, but this also seems implausible as a cause since it should only keep me from getting out of park, as I understand.

Codes that I think could possibly be involved (I don't know how many of these are old; I did clear codes but don't know if the logs from VCDS keep old codes as well; I need to learn about this) -

Address 03: ABS Brakes Labels: 4D0-907-379-ABS.lbl
Part No: 4D0 907 379 L
Component: ABS/EDS BOSCH 5 4171
Shop #: BB 34171
VCID: 377325A615F1A286AC-515A

1 Fault Found:
00526 - Brake Light Switch (F)
27-10 - Implausible Signal - Intermittent

Address 02: Auto Trans Labels: 01L-927-156.lbl
Part No: 4D0 927 156 K
Component: AG5 01L 4.2l4V RDW D26
Coding: 00011
Shop #: WSC 93009
VCID: 31671BBEFB957CB6E2-5178

4 Faults Found:
18258 - Powertrain Data Bus
P1850 - 35-10 - Missing Message from ECU - Intermittent
18157 - Transmission Control Unit Incorrectly Coded
P1749 - 35-10 - - Intermittent
17114 - Gear Ratio Monitoring
P0730 - 35-00 - Incorrect Gear Ratio
17087 - Brake Switch (F)
P0703 - 35-00 - Electrical Malfunction

nyrobbie77

I can't help you with the codes but it definitely sounds like trans is in limp mode. There is the F125 switch on the driver side of the transmission which could be giving you issues. I've put a link below to the replacement procedure. Might be a good place to start before looking into transmission overhaul. If you weren't aware, transmission failures on these cars are fairly common.

audipages A8 F125 Transmission Switch Replacement

also, when in limp mode, the PRND432 lights will all light up at once. doubtful it is a separate fault.

hillpc

Now I conclude that the gear selector cable must have some kind of problem. Car won't even crank now. Had my daughter move the selector through all the ranges while I looked at the F125 switch underneath. No movement whatsoever. Thought it was moving very easily the last time I checked. I also can't feel a detent for reverse. I'll be pulling off the console to investigate.

albundy3670

It's a good idea to pull the console off.
Cable broke at the shifter on my car after I let it sit for a year.
Most likely could have avoided replacing the shifter by using a penny's worth of lube.
Limp mode is not usually a good sign.
Wish you the best with the car

hillpc

The very end of the gear selector cable, where it hooks to the gear selector, is a round plastic ring that is pushed and pulled by the gear selector. Plastic broke, so the selector was pushing on nothing. I can push and pull the broken ring (and thus the cable all the way down to the trans) by hand, though. I can feel the right number of clicks for PRND432 when I work the cable by hand, so there must be detents in the valve body or in the F125 switch. I'm going to try to start it and see if it drives normal by selecting the gear ranges in this manner. When I last tried to start the car, it wouldn't crank and the display read "4".

Taking off the console was a pain; I eventually resorted to partially removing the parking brake handle so I could get the console up and over it. Even though the Bentley manual didn't say to do this, I couldn't see any other way to get the console from being obstructed by the parking brake handle, even after I had all the bolts out of the console.

nossisnave

[QUOTE=hillpc;24736413] Does the selector cable manually work something in the valve body, which could be binding when warmed up?

Hey hillpc
Just to answer your question yes there is a selector that is moved for the different gear options. Here is what it looks like inside my 02's transmission. When we reinstalled mine, I couldn't get it to go into Park, the first pic shows where I had mislocated the pin.

hillpc

picture's worth a thousand words; thanks.

hillpc

I checked continuity of the various 8 terminals on the F125 switch as instructed by the Bentley manual and found a whole bunch of failures. I've seen F125's available on Rock Auto at $194 (Standard Motor Products) and $317 (Airtex/Wells). Both have a 3-year warranty. There's a guy on ebay in the UK selling a used one for $168 or best offer.

I'm thinking about drilling out the rivets and taking it apart. Anybody know what goes wrong with these? If it's something I can simply clean up I could nut and bolt (or rivet) it back together.

nossisnave

I would imagine issues would be due to the insulation breaking down and having one or more shorts going on between the wires, but what do l know? IIRC on the inside the wires are submerged in trans fluid.

Whatever it is, if you do decide to perform surgery on the F125, please, please, please take lots of photos and post 'em. That seems like it would be an invaluable resource to have access to.

hillpc

The switch is dry inside; it's bolted to the outside of the trans.

Attached are some pictures. I drilled the heads off the rivets, punched them out, and it came right apart. You can see the plastic "wheel" in the middle that is driven by the shaft coming out of the trans. It has 3 levels of bumps or ramps that push in on at least 2 separate switches with 3 levels of metal followers that climb up and down the ramps as the wheel turns with gear position. The wheel can be put upside down, it seems, presumably scrambling the logic of which combination of which switch contacts means which gear, so pay attention which way it's installed if you take it apart. (I didn't). I imagine the plastic ramps could get worn down and not push the switches deep enough anymore.

I didn't see anything obvious wrong, and couldn't figure out a way to dig deeper so I bought a new switch from Autozone for $200. It read all the continuities correctly from the Bentley instructions "Multi-Function Transmission Range (TR) Switch -F125- with 8-pin connector, testing" if I numbered the 8 pins COUNTERCLOCKWISE, not clockwise as in the Bentley manual. The manual has the same drawing for checking the switch and the voltage supply to the switch, which are on different halves of the connector, which seems to be an error (or at least misleading) to me. It does say "Contacts on -F125-1)", but I don't know which half of the connector this is. Obviously one needs to check on the switch side.