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Discussion Starter · #1 ·
Ahhh, the latest with the problem child.

Went to start car about a week ago and no joy. Found out that starter was not enabling due to SMG. No codes at the time.
After re-trying got it to start and moved the car to where I can work on it.

NOW (car has sat a bit), I get the following error codes (not all the time after clearing codes):
2B0F - DME: SMG shift sequence monitoring
4FA0 - SMG: Clutch (activation, position deviation)
5101 - SMG: Hydraulic pressure sensor --also at one point in INPA the pressure read ~108 bar, which I don't believe.

Kind of stumped, thought I had this thing running well with regards to the SMG. Other than the above it shifts/runs very very well.
Also, after clearing codes all is well until I step on brake then it throws a RCOD immediately. Start does not enable.

Any ideas?

PLCD sensor wiring perhaps? Maybe hydraulic pressure sensor kaput?

The other weird thing is that when sitting in the driveway after turning off the ventilation system, it kept coming back on! WTF?!
 

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Possible sensor or harness sure. At those pressures tho one can hear the pump pitch drop. Do you hear the pump running all the time / low pitch? If so maybe the pump relay got stuck. Or if the pump cycle is too quick (i.e. pump turns on and pressure instantly goes to 100+) then your accumulator is likely shot. Post a video of how the pump sounds when you unlock/open the door.
 

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So pump was off and not running until pressure read 108 bar? Leaning towards harness as plcd and pressure sensor harness is shared. For whatever it's worth I've never read about a pressure sensor failing.

What do you mean by 'kept coming back on'?
 

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wiring for the pump at the top of the unit is a real possibility since the casing for the wires deteriorates over time from heat and if you removed the transmission or engine recently it could have shaken them up.
 

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The second pictures showed the issue (4FA0 position deviation). The slave didn't move correctly, it moved almost 1/3 the required distance. The clutch valve or the slave is leaking IF the accumulator is still good enough and no air in the system.

When the pressure is low enough below 40 bar, run the pump manually the pressure build up should struggle initially, if this happen then the accumulator is good still functional.

Bleed the clutch and test by pressing the brake with ignition ON engine OFF, the PLCD should show 190-230 (depends on the adapted value) for full slave extension, start the engine, the slave should move to 190-230.

If there is a leak it would fail the clutch valve adaptation.
What is the accumulator test value?.
Also, after clearing codes all is well until I step on brake then it throws a RCOD immediately. Start does not enable.
This also sounds like accumulator issue or as mentioned above, clutch valve or slave. 108 bar sounds like sudden pressure surge back to lower block.
2B0F - DME: SMG shift sequence monitoring
Does this fault and the fault list above happen during driving and shifting?. If yes it also point toward accumulator or clutch valve or slave leak, but also could be a top solenoid leak during shifting, but if you step on the brake and pressure suddenly drops then we are back to accumulator, clutch valve and slave issue.
What is the history of this SMG?.
 

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Discussion Starter · #9 ·
Ok, let me kind of type this out...

The history of the SMG is as follows:
SMG came with car, did not run. During the process of reviving the car, the gear position sensor wiring was repaired, all solenoid o-rings were changed to viton Shore 75A o-rings, new fluid. Car ran say 8-9000mi like this.
Some time later I had choppy shifting and subsequently adaptation failures, changed the slave (MLR reman), cleaned out the hydraulic pump electric motor, put new pump seals (MLR) in the hydraulic pump, new pump relay, replaced clutch arm, pivot, and release bearing. My issue for failing adaptation was the slave cylinder modulating piston seal failure (presumably, as it was trashed). Car shifted awesome after this, really no complaints.....until this problem occurred. The accumulator tested about 1 bar below the min pressure spec.

Today, I have changed the following out from a spare SMG trans assembly I have:
-PLCD sensor/sub-harness
-Pressure sensor (I am skeptical that this was an issue, but changed it anyhow)
-Accumulator (this accumulator tested within spec, about 1 bar above minimum range at ~20C hydraulic temp)
I have bled the clutch/actuator block (1 cycle) due to the accumulator/pressure sensor change, and ran adaptation, but it is still failing adaptation (only one PLCD sensor screw right now if that matters). I will run the bleed cycle a few more times and see if it passes the adaptation...I am not sure how much more of the gong-bong-wallet sound I can take though.

I will probably not be able to resist watching manual transmission swap videos tonight...
 

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It is not the accumulator, PLCD, or pressure sensor, but seems air in the system. The pressure sensor fault triggered when the pressure sore above the normal operating range.

For further investigation, the real question here why air was introduced?. were there enough oil in the tank?. pump suction inlet O'ring replaced during the pump overhaul?. Another area is the top shift block piston seals started to wear but I would expect that to be combined with oil level decrease.
Possible the system started to wear and require bleeding every 10,000 mile.
 

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Don't rule out the relay that was mentioned. Also did you scrape the stampings off of the motor brushes?

The nice thing about using INPA is you can watch things and make things happen. I wouldn't say that I have never seen my pressure off the scale with the oil cold and the trans in S6. What is you bleed down time? Remember most of the trouble comes from trying to make the BMW engineers hiding in the SMG controller happy.
 

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Discussion Starter · #14 ·
This smg seems very tight, holds pressure well. From accumulator released to pump shutoff when charging is about 11s. Could be air I suppose but fluid level was correct, I struggle to see how it could be air, but understand a symptom or two lining up with that. I do not think high pressure lines up with air in system though..

When I put the tank on I do it twice in order to check no Orings are tweaked. Have to get gaskets and put exhaust on, then will post more.

I also thought accumulator lowish pressure was no factor, was also at low temp, so precharge pressure will come up with temperature.
 

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The bleed down time is from pump shut off to pump start, include pressures. It should be several minutes at least, on a tight system that is cold it could be 1/2 day. The reason I ask is because even though you have done the seals one may have been damaged? Also there was another thread that had new pump seals that had been worn away after 10k miles. If the pressure is bleeding down in less than say 5min cold you are going in deep again.
 

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Discussion Starter · #17 ·
Ok, have the car running. All seems well.
Basically I changed to another PLCD sensor/harness, swapped for a slightly better accumulator, swapped to a used spare pressure sensor, bled it multiple times, and adaptations.

Also have Redline D4 in it, shifts awesome.

Only gripe I have is it weeps gearbox oil at a transmission case flange. Anyone have a recommendation for a wicking sealant?
 
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