Tiptronic code P0735

[ron.in.irvine]

OK, so maybe I got a bit ambitious when washing my '97 Boxster when I was changing the engine air filter.

After driving 20 or so miles on a very dusty dirt road a few weeks ago, this morning I decided to check (and probably change) the engine air filter. When I pulled the engine cover there was a thick layer of very fine dust on everything. Seeing no harm in doing so, I hosed off the engine until everything looked clean and went ahead and changed the air filter. I hosed off the underside of the car to wash away whatever dust was hiding there, put everything back together, raised the top and washed the car.

When I went to take it for a drive the automatic transmission didn't want to engage, finally did, and then started flashing the "4th gear" and "D" lights. Looks like limp home mode. Checking the OBD code, I see a P0735 which says that the transmission has selected the wrong gear.

Not believing in coincidence, I'm thinking that I've done something wrong and can't quite figure out what because I hate to believe that a transmission can starting tossing out fault codes just from getting damp. Other than splashing around a bit of low pressure water, the only other thing I did was to move a fat rubber-coated armored cable that runs fore-and-aft over the top of the engine to one side and then back as I was cleaning things and checking the tightness of clamps on the intake system.

So that armored cable was the gear selector cable? Is there some adjustment I could have screwed up but can go back and fix? Is the water a contributing factor? Anybody else have this experience and recover from it easily?

[Loren]

OK, so maybe I got a bit ambitious when washing my '97 Boxster when I was changing the engine air filter.

After driving 20 or so miles on a very dusty dirt road a few weeks ago, this morning I decided to check (and probably change) the engine air filter. When I pulled the engine cover there was a thick layer of very fine dust on everything. Seeing no harm in doing so, I hosed off the engine until everything looked clean and went ahead and changed the air filter. I hosed off the underside of the car to wash away whatever dust was hiding there, put everything back together, raised the top and washed the car.

When I went to take it for a drive the automatic transmission didn't want to engage, finally did, and then started flashing the "4th gear" and "D" lights. Looks like limp home mode. Checking the OBD code, I see a P0735 which says that the transmission has selected the wrong gear.

Not believing in coincidence, I'm thinking that I've done something wrong and can't quite figure out what because I hate to believe that a transmission can starting tossing out fault codes just from getting damp. Other than splashing around a bit of low pressure water, the only other thing I did was to move a fat rubber-coated armored cable that runs fore-and-aft over the top of the engine to one side and then back as I was cleaning things and checking the tightness of clamps on the intake system.

So that armored cable was the gear selector cable? Is there some adjustment I could have screwed up but can go back and fix? Is the water a contributing factor? Anybody else have this experience and recover from it easily?

P0735 Gear monitoring, 5th gear - signal implausible

ATF level not OK

Mechanical/hydraulic fault in transmission. (e.g. solenoid valve does not operate despite correct electrical triggering)

- Solenoid valves

- Valve chamber

- Transmission

So, if the ATF level is good then you likely need to put a PST2 or PIWIS on the car and run the Tiptronic diagnostics.

[xflyboyx]

This might help!!! (see attached file)

P0735_tiptronic.pdf

[pk2]

In genreal, spraying a motor down without covering tightly every electrical connection and breather is trouble. My guess is your trans. is fine but electrics are compromised. You could go over every place you sprayed and look for any and all electrical connections , pull them off, make sure all is dry maybe spray them with contact cleaner and put them back together. If you didn't burn short anything out might just get up and go

PK

[ron.in.irvine]

Just as a note to those who are trying to help me, there were no problems and apparently nothing wrong before hosing the engine bay and underside of the car. I really do not believe in a coincidence strong enough to allow a transmission problem to show at the very instant the car was restarted after I washed things and jiggled an armored cable. And I'd like to think that water in no greater volume than might be splashed up into the engine bay by driving through a puddle at speed isn't to blame. Otherwise I can never trust driving this thing on a rainy day ;)

Anybody know if the armored cable (rubber coated and roughly 5/8" in diameter) which runs from the passenger compartment, over the top of the engine (and I mean over the top of the intake plumbing and throttle body), and then down toward the transmission is actually the shift cable?

My Bentley Service Manual does show (section 37-11) some sort of clip/retainer on the selector cable at the transmission end - could I have dislodged the clip by moving the cable back and forth? Bentley also indicates (section 37-16) that the transmission range switch (aka gear position switch aka multi-function switch) - which gives gear selection info to the Tiptronic control module is attached to the selector cable or at least to a Bowden cable which the selector cable clearly is.

Here's what I'm thinking: I either diddled the adjustment/positioning/attachment of the cable by moving it around in the engine bay and/or wetting the switch has caused it to short and give wrong data to the control module.

Anybody have any other thoughts?

[wvicary]

Water could have traveled down the shifter cable and gotten into something. I would clean the connections at the transmission and see if that solves the fault.

[timbo]

That is the shift cable. It's possible some water got onto a contact or electrical component which has interfered with the signal it was sending. As others have said, dry everything spray with a water repellant like WD40. Perhaps if you then reset the computer by disconnecting the battery for a few minutes all will be well?

[ron.in.irvine]

No, the wiring isn't as waterproof as I thought it would be and, yes, it all turned out OK.

Unplugging the connector of the wiring harness (running from the control unit in the rear trunk down to the transmission) allowed a slug of water to gush out. Turns out that a good portion of the harness inside the sheathing was filled with water - apparently the waterproofing was keeping water in rather than out.

Where it entered the harness I have no idea but draining it, drying everything, and cleaning the connectors restored the transmission to smooth operation.

Just as a note to those who are trying to help me, there were no problems and apparently nothing wrong before hosing the engine bay and underside of the car. I really do not believe in a coincidence strong enough to allow a transmission problem to show at the very instant the car was restarted after I washed things and jiggled an armored cable. And I'd like to think that water in no greater volume than might be splashed up into the engine bay by driving through a puddle at speed isn't to blame. Otherwise I can never trust driving this thing on a rainy day ;)

Anybody know if the armored cable (rubber coated and roughly 5/8" in diameter) which runs from the passenger compartment, over the top of the engine (and I mean over the top of the intake plumbing and throttle body), and then down toward the transmission is actually the shift cable?

My Bentley Service Manual does show (section 37-11) some sort of clip/retainer on the selector cable at the transmission end - could I have dislodged the clip by moving the cable back and forth? Bentley also indicates (section 37-16) that the transmission range switch (aka gear position switch aka multi-function switch) - which gives gear selection info to the Tiptronic control module is attached to the selector cable or at least to a Bowden cable which the selector cable clearly is.

Here's what I'm thinking: I either diddled the adjustment/positioning/attachment of the cable by moving it around in the engine bay and/or wetting the switch has caused it to short and give wrong data to the control module.

Anybody have any other thoughts?

[JWH7]

A very interesting problem as I had a similar experience with my 06 Cayenne S. Hit a small puddle with the right front wheel and lost third gear during a 2nd to 3rd automatic upshift. I had manual control for a couple of miles and then transmission went into default mode. Made it to dealer in 2nd gear. Fault code was P0735. Dealer cleared faults and reset adaptations. Problem hasn't occurred in a month, but I am concerned because they never found a cause. Maybe I need to check some connections too.