Data Details:
I've been trying for months to collect the right data to show why my transmission is going into limp mode, but it has proven most challenging. No one tool seems to give accurate and thorough results, thus a video was the only good way to capture all this data from different sources using screen record. Example, the wheel sensor speeds read fine on multiple ODBII scanners until the car hits 30 MPH. After that, I believe the ODB bus is too slow to keep up and it loses synch..
I tapped into the CAN bus for more data. It reliably gives me the wheel sensor info, braking, RPM, what gear is selected by the Tip, and limp mode. It has a value which indicates whether the gear shifting is stable or still in progress and that seems to track. Another gives some indication on the torque converter status, but I'm not sure I have the interpretation correct for that one. I have the raw CAN data captured in addition to the video, but it is tedious to look through.
I also tapped into most of the raw Tip signals with an oscilloscope: Transmission input speed sensor, MV1-3 solenoids valves, and EDS 1-4 regulator/valves. The MV1-3 solenoids are either on or off. On the video, if they're off, they're 12 V and on if they're zero to a few volts. The pressure regulators are pulse width-modulated. When not actuated, but not in limp mode, they seem to give a low-duty-cycle (low energy) pulse to each regulator. When the regulator is active, that jumps up closer to 50% duty cycle. It's easy to see that on the scope signals OR on the measurements below. When in limp mod
I couldn't get the transmission input speed from the CAN bus, so I captured that, the RPM, and the output speed on another scanner. The transmission input sensor raw signal seems to track with what I see on the scanner.
Observations:
The valve signals seem to track the "Valve Body Signals.png" file I attached. EDS4 is supposed to be used to engage the TC clutch, but I don't see it getting turned on strongly. According to the chart, it shouldn't engage at all until 3rd or higher. Even in park or neutral, it's getting a small duty cycle but that seems normal.
This video shows 3 failures:
1) In second gear starting from a stop - Note the input signal starts slowing until it stops while the engine is revving.
2) In second gear, but you can see 3rd slipping right before - Same thing on the input signal falling off
3) It seems to go into limp mode in terms of shutting off all the valves, but the CAN data doesn't show full limp mode - it does show some value which seems related so maybe it knows it will be going there soon..
I didn't trap 5th gear slipping and going into limp mode this time, but have seen it in the past. It acts the same. It's stable and in 5th, then the engine starts revving higher (slipping), then it goes into limp.
Watch these in HD:
YouTube Limp Issues Full video
YouTube Limp Issues Slo Mo 1
YouTube Limp Issues Slo Mo 2
YouTube Limp Issues Slo Mo 3
Hey
@ronegarnett
, wow, that is some seriously impressive data collection you've done to chase down this Tiptronic limp mode, especially tapping into the CAN bus and using an oscilloscope. With all this great electronic data pointing towards slippage, what's the history of the transmission fluid and filter? Sharing a bit about its condition or the last time it was serviced might help the folks here connect the dots with the sensor readings you've captured.
