Strange SMG issue

[s54juulien]

Hi All,

I have a 2002 M3 with 141K that has the SMG gearbox. I've recently been having some weird issues that I'm hoping someone here might have encountered.

One day I got to work and left my car in neutral, and when I went back to move it; it wouldn't go into gear. I tried to restart the car and it wouldn't even start up. A week and a new EWS module later and the car fired right up, but I was left with a new different problem. When I first start the car up everything works fine but if I wait too long before selecting 1st or reverse it won't go into gear. If I restart the engine and select a gear it works just fine, I just have to do it within 10 seconds. The other issue is that at stoplights or in traffic as soon as I come to a stop it pops into neutral and requires an engine restart to go back into gear. As you can imagine this is not ideal and the car has been parked again for the past week.

I have changed the salmon relay which didn't do anything and checked all fuses. I have looked at live data with my Schwaben scan tool and my hydraulic pressure has not gone below 48. Temperature sensors all look good. The only thing that stood out to me from the live data is that it said "Shift lock: enabled" Does anyone know what the shift lock is on the SMG and if it can ever go bad? What is also interesting is that if I try to force the transmission to go into gear (when it won't cooperate with the shifter) It doesn't work.

The error codes I can read are 3B - SMG: Actuation, clutch, dynamic & 57 - SMG: Fault, test function. They are able to be cleared.

I have tried to bleed the system and add hydraulic oil as my level was low. This did not change my problem. I am also not sure where the hydraulic fluid could have gone as the hydraulic pressure is good and I do not see any leaks other than a little seepage from the reservoir to the pump.

I am pretty sure my problem is either air in the hydraulic system, my accumulator, or an electrical gremlin. Any similar experiences or tips to try next would be very much appreciated. Thank you in advance!

[Arehman]

Your pump is weak from the sounds of it. PM me I have good used/ tested ones if you need.

[oceansize]

The 3B is almost, keyword almost, always clutch slave. The PLCD sensor referenced by this error is inside the clutch slave and cannot be purchased by itself.

[eacmen]

When you bled the system did you also do adaptations?


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[s54juulien]

The 3B is almost, keyword almost, always clutch slave. The PLCD sensor referenced by this error is inside the clutch slave and cannot be purchased by itself.

So after trying to bleed the SMG system it started pissing hydraulic oil all over the place. I got under the car and was able to see that my leak was coming from the slave. I replaced the slave cylinder and performed both bleed procedures on the slave and the actuator successfully. When I attempt to teach in characteristic clutch values, the operation fails. I am unable to teach-in clutch slip point as the car will not start. If I unplug the slave cylinder the car will fire right up but will not go into gear (obviously). I think the issue must be a hardware issue with the release bearing or fork.

I would really appreciate any other insight you all can give me. Starting to think I might be better off starting the 6SPD swap

[oceansize]

So after trying to bleed the SMG system it started pissing hydraulic oil all over the place. I got under the car and was able to see that my leak was coming from the slave. I replaced the slave cylinder and performed both bleed procedures on the slave and the actuator successfully. When I attempt to teach in characteristic clutch values, the operation fails. I am unable to teach-in clutch slip point as the car will not start. If I unplug the slave cylinder the car will fire right up but will not go into gear (obviously). I think the issue must be a hardware issue with the release bearing or fork.

I would really appreciate any other insight you all can give me. Starting to think I might be better off starting the 6SPD swap

Before we go any further, brand new slave or used/reman slave?

[sapote]

If I unplug the slave cylinder the car will fire right up but will not go into gear (obviously). I think the issue must be a hardware issue with the release bearing or fork.

Unplug the electrical connector or the whole thing?
I think it didn’t crank due to low pressure-leaking , but why disconnect the connector stopped leaking?

[s54juulien]

Before we go any further, brand new slave or used/reman slave?

Brand new from BMW

[s54juulien]

Unplug the electrical connector or the whole thing?
I think it didn’t crank due to low pressure-leaking , but why disconnect the connector stopped leaking?

I unplugged the electrical connector on the slave cylinder. Could it be possible the connection on the wiring harness side of things is bad?

[sapote]

So after trying to bleed the SMG system it started pissing hydraulic oil all over the place. I got under the car and was able to see that my leak was coming from the slave. I replaced the slave cylinder and performed both bleed procedures on the slave and the actuator successfully. When I attempt to teach in characteristic clutch values, the operation fails. I am unable to teach-in clutch slip point as the car will not start. If I unplug the slave cylinder the car will fire right up but will not go into gear (obviously). I think the issue must be a hardware issue with the release bearing or fork.

It sounds like the slave position sensor signal is bad: During starting, by default computer disengaged the clutch, then after 10 sec it will release the clutch if in neutral - this explains why you could not shift after 10sec.
If replaced with new slave from dealer, then I would double check the connector and wiring to the slave.

[s54juulien]

It sounds like the slave position sensor signal is bad: During starting, by default computer disengaged the clutch, then after 10 sec it will release the clutch if in neutral - this explains why you could not shift after 10sec.
If replaced with new slave from dealer, then I would double check the connector and wiring to the slave.

Thank you, Sapote. Any tips for how to check the wiring? Thinking I'll just spray it with brake cleaner and try to remove all grease. Do you think if this sensor was bad it would still allow me to shift into 1st and reverse?

[eacmen]

Thank you, Sapote. Any tips for how to check the wiring? Thinking I'll just spray it with brake cleaner and try to remove all grease. Do you think if this sensor was bad it would still allow me to shift into 1st and reverse?

I would physically inspect the pins on the clutch slave connectors as well as inspect the pins on the SMG ECU. Look for corrosion or dirt.

Also strange things happen with bad grounds. You mentioned EWS needing to be replaced. Seems coincidental but could indicate a more systemic issue with the electrical system.


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[s54juulien]

I would physically inspect the pins on the clutch slave connectors as well as inspect the pins on the SMG ECU. Look for corrosion or dirt.

Also strange things happen with bad grounds. You mentioned EWS needing to be replaced. Seems coincidental but could indicate a more systemic issue with the electrical system.


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I will do my best to inspect all the pins and clean them. Gonna go pick up some electrical contact cleaner this weekend. Hopefully, this works. Ill report back next week.

[sapote]

I have not used contact cleaner; good contact is when metal rubbing metal when they mate.

[s54juulien]

Just wanted to update the thread. Ended up going with a manual swap. The Clutch and all hardware looked good, so it was certainly an electrical gremlin. Thank you for all your help! Looking forward to having 3 pedals.