GearBox.

[Henrym3]

Today while driving with everything working perfect I come off a roundabout at around second gear speed when suddenly the X slips into 5th gear with subsequent massive slippage of gear. No lights/warnings. Pretty level ground so decide I can get home. About 1 mile later trans failsafe warning comes on. I get home and find reverse is good/normal engages fine no slip, select drive and straight to 5th. Battery is good no recent flat battery problems getting between 13.8 to 14v on gauge. Check codes.


This is the result. Can anyone pick fault with those solenoid readings or advise on where to start looking for the interrupted signal.
Readings were taken after clearing codes and moving backwards 10 feet and then forward.
Much appreciate anyone reading and look forward to your comments.


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[RRPhil]

Originally Posted by Henrym3

Can anyone pick fault with those solenoid readings.....

156mA is the minimum solenoid current (i.e. solenoid is off) and 780mA is the maximum solenoid current (i.e. solenoid is fully on). The exception to this is Pressure Actuator (i.e. solenoid) 1 which sets the mains pressure and this works the opposite way around. It defaults to maximum pressure when no current is applied. This is so the transmission can limp home in failsafe mode if the transmission loses all electrical power.

Your table shows Pressure Actuator 1 at 156mA, which you would never normally see unless the transmission were on wide-open throttle transmitting maximum torque. Usually, you would expect to see a much higher current than this as the controller modulates the mains pressure in proportion to engine torque to ensure smooth engagement of the clutches. This implies that the transmission is in failsafe mode (i.e. defaults to maximum mains pressure).

Pressure Actuator 4 controls the torque converter lock-up clutch, so 156mA on this solenoid just means the LUC is not activated (low gear/low speed). On the other hand, it could also mean the transmission is in failsafe mode as the LUC is deliberately not engaged in failsafe.

That leaves solenoids 2, 3 & 5. According to your table, solenoids 2 & 3 are fully on and solenoid 5 is fully off. This combination would normally arise only in 3rd gear but, even then, you would never expect to see 2 & 3 at maximum current unless the car was accelerating on WOT. Clearly, therefore, these values are not normal.



Phil

[Henrym3]

Originally Posted by RRPhil

156mA is the minimum solenoid current (i.e. solenoid is off) and 780mA is the maximum solenoid current (i.e. solenoid is fully on). The exception to this is Pressure Actuator (i.e. solenoid) 1 which sets the mains pressure and this works the opposite way around. It defaults to maximum pressure when no current is applied. This is so the transmission can limp home in failsafe mode if the transmission loses all electrical power.



Your table shows Pressure Actuator 1 at 156mA, which you would never normally see unless the transmission were on wide-open throttle transmitting maximum torque. Usually, you would expect to see a much higher current than this as the controller modulates the mains pressure in proportion to engine torque to ensure smooth engagement of the clutches. This implies that the transmission is in failsafe mode (i.e. defaults to maximum mains pressure).



Pressure Actuator 4 controls the torque converter lock-up clutch, so 156mA on this solenoid just means the LUC is not activated (low gear/low speed). On the other hand, it could also mean the transmission is in failsafe mode as the LUC is deliberately not engaged in failsafe.



That leaves solenoids 2, 3 & 5. According to your table, solenoids 2 & 3 are fully on and solenoid 5 is fully off. This combination would normally arise only in 3rd gear but, even then, you would never expect to see 2 & 3 at maximum current unless the car was accelerating on WOT. Clearly, therefore, these values are not normal.







Phil

I much appreciate your input as the forum guru and forgive my ignorance but does this look like an electrical issue ie bad connection or a solenoid issue. Again much appreciate your input


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[RRPhil]

There’s no indication that you have a solenoid issue. It’s more likely that the readings have come about as a result of the transmission going into failsafe mode. The question is, why?

How certain are you that your transmission is selecting 5th gear, rather than 4th? I ask because 4th gear is the default on the 5HP24 and this could be significant. If it definitely is 5th gear, then that would indicate a fault with your A-clutch.

Phil

[Henrym3]

Originally Posted by RRPhil

There’s no indication that you have a solenoid issue. It’s more likely that the readings have come about as a result of the transmission going into failsafe mode. The question is, why?

How certain are you that your transmission is selecting 5th gear, rather than 4th? I ask because 4th gear is the default on the 5HP24 and this could be significant. If it definitely is 5th gear, then that would indicate a fault with your A-clutch.

Phil

I have no evidence that it is 5th gear, just feels awful and obviously slips. More than likely it is 4th. I did a quick check of wheel speeds and the sensors all work and read same speeds if that helps.


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[Henrym3]

Originally Posted by Henrym3

I have no evidence that it is 5th gear, just feels awful and obviously slips. More than likely it is 4th. I did a quick check of wheel speeds and the sensors all work and read same speeds if that helps.


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I should add the oil and filter was changed at 100k/150k and due again at200k currently on 176k. All parts are BMW.


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[80stech]

We are very lucky to have RRPhil!

[Henrym3]

Originally Posted by 80stech

We are very lucky to have RRPhil!

Aren’t we just.


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[RRPhil]

If you start the transmission from cold, will it shift normally for a few minutes before the fluid gets warm and locks into 4th/5th or does it go straight into 4th/5th as soon as you select Drive?

Phil

[Henrym3]

Originally Posted by RRPhil

If you start the transmission from cold, will it shift normally for a few minutes before the fluid gets warm and locks into 4th/5th or does it go straight into 4th/5th as soon as you select Drive?

Phil

Straight to 4/5 as soon as D is selected. Just as a comment I have had paddle shift fitted for 5/6 years and 2 days before this happened they stopped working I just put it down to something that needs looked at. Just mentioned in case it points you to something. Cheers


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