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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHLimp Mode videos, 2001 996 C4
Leading reported evidence
Check level
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
The fluid is correct for that vehicle and I've checked the level when it was running and I'm the temperature zone multiple times.
Leading evidence: 'Check level' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'pump pressure is low' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check level' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
The ATF is essentially brand new now and I've checked the level multiple times.
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Discussions that suspect a cause
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Suspected cause
If it's randomly slipping in all gears it's likely the pump pressure is low.
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Suggestion
I know nothing about the ZF box; if there is a way to put a gauge on it to check pump pressure I would start with that.
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Suggestion
I would change the ATF to the proper spec first thing.
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Suggestion · Original poster
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.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
9 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T222516Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
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
Your Mercedes Tip goes into limp mode AFTER it starts slipping?
If so the slipping is causing the limp mode, not the other way round.
My Mercedes Tip would occasionally slip in 2nd and each time it immediately went into limp mode. In that case limp mode is totally expected because the two speeds sensors don't match.
I wish it were the 2002 Tiptronic common with Mercedes! That's are a lot more transmission mechanics for that one.
You are 100% correct that the slipping is leading to limp mode, or so it appears. I'm just trying to determine why it's slipping. It's supposed to be totally rebuilt, it is it something in the valve body, the torque converter, the pump, etc.?
I would change the ATF to the proper spec first thing.
If it's randomly slipping in all gears it's likely the pump pressure is low. I know nothing about the ZF box; if there is a way to put a gauge on it to check pump pressure I would start with that.
There is no way to measure the pressure and no sensor. I wish! The ATF is essentially brand new now and I've checked the level multiple times. I think you're right that the pressure must be low, either because of the valve body, the pump, or maybe the torque converter.
I'll probably end up dropping it again, but wanted to make sure the data supports the conclusion.
You appear to have the ATSG book for the ZF box. Do they show a pump pressure regulator adjustment? If so I'd turn it up all the way.
My comment about ATF is to ensure the correct fluid is installed. Some ATF is "slipperier" than others.
I'm surprised there is no pressure test port. I have an Asin TR-60 transmission in my Cayenne and it's got pressure test ports on the outside of the box for most internal pressures. It's also got an adjustable pressure regulator in the valve body.
I have several little manuals/documents for the same general model, ZF 5HP19. None specifically mention Porsche, but the signals seem to match. There are no pressure test ports nor adjustments. I wish!
The fluid is correct for that vehicle and I've checked the level when it was running and I'm the temperature zone multiple times.
It will be running along fine, then all of a sudden, the input to the transmission falls off until limp mode kicks in and it pops back up.
Limp mode shuts off all solenoids and valves. It runs fine in limp mode, other than being slow to get going from a stop. The torque converter clutch is obviously not engaged, but the torque converter is not slipping in that mode. That leads me to believe the problem is in the valve body, but not 100% sure.
I occasionally get a torque converter valve error, but not every time. The errors I get basically say it's slipping, which I already knew.
Thanks for your ideas! 🙂
Limp mode usually gives you one gear in forward, typically 3rd so slow acceleration is expected.
Have you considered buying another ZF box from a junkyard? Must be plenty out there.
The limp mode gear is 4th, but otherwise true - slow off the line. I am currently looking for a new valve body but a completely different one might be an option too.
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