Exhaust Flap Servomotor - 2014 R1200RT

[Michiganr80rt]

The check engine came on yesterday. Motoscan shows three exhaust flap servo motor errors; 21FA20, 21F502, and 21F500. I cleared the codes and they came back when I turned the key back on before I started the bike. From web search it looks like these are from an electrical fault in the motor. Max BMW shows the servo unit as a $326 part. There is also a $70 "Servo Buddy" or a $60 "Healtech Exhaust Servo Eliminator" that lets you disconnect the servo but the bike computer thinks it is still there.

 

Has anyone replaced the servo motor and how involved a job is it? Was it necessary to have the computer map the new servo motor or did everything work "plug and play"?

 

Has anyone used either of the servo eliminators? Did you do anything to lock the exhaust flap full open?

 

I will be pulling the exhaust soon to check what position the flap is in and if the flap is stuck. I can also check if the motor is dead or if the flap is moving.

 

Thanks in advance for any help.

 

[dirtrider]

24 minutes ago, Michiganr80rt said:

The check engine came on yesterday. Motoscan shows three exhaust flap servo motor errors; 21FA20, 21F502, and 21F500. I cleared the codes and they came back when I turned the key back on before I started the bike. From web search it looks like these are from an electrical fault in the motor. Max BMW shows the servo unit as a $326 part. There is also a $70 "Servo Buddy" or a $60 "Healtech Exhaust Servo Eliminator" that lets you disconnect the servo but the bike computer thinks it is still there.

 

Has anyone replaced the servo motor and how involved a job is it? Was it necessary to have the computer map the new servo motor or did everything work "plug and play"?

 

Has anyone used either of the servo eliminators? Did you do anything to lock the exhaust flap full open?

 

I will be pulling the exhaust soon to check what position the flap is in and if the flap is stuck. I can also check if the motor is dead or if the flap is moving.

 

Thanks in advance for any help.

 

Afternoon  Michiganr80rt

 

You might start by verifying the flapper valve is not stuck (that it can turn), if it is frozen up then you can possible address that with lubrication.  

 

If the valve is stuck it can force the motor to draw higher amps. 

[Michiganr80rt]

39 minutes ago, dirtrider said:

Afternoon  Michiganr80rt

 

You might start by verifying the flapper valve is not stuck (that it can turn), if it is frozen up then you can possible address that with lubrication.  

 

If the valve is stuck it can force the motor to draw higher amps. 

That is my plan when I get the bike on the lift.  Does the computer move the flap when the key is turned on before starting the engine?

 

[Stiggy]

I believe that when you first turn the key, the flap positions itself for starting. So yes...

[Randyjaco]

I just ground the butterfly off its axel. No negative effects to performance. My servo/axel still work, but when they stop, I'll go with the eliminator. The flapper is just useless crap.

[Stiggy]

Verrrry interesting 

 

The purpose of this system according to the motorcycle manufacturers’ marketing departments is to create back-pressure at lower RPM’s to increase torque. Unfortunately, this probably isn’t the real reason; the true purpose of the exup valves is to meet noise regulations. The exhaust valves are partially closed at idle and low rpm to reduce noise, and closed again at the upper RPMs to meet peak noise regulations. The proof of this has been shown on the dyno where removing the valves and retuning the engine creates a flatter better torque curve. Additionally, in the USA, most bikes close the valve again at the upper RPM range, but in Europe they do not (different regulations) and the European bikes typically create a few more HP on the top end as a result.

 

https://rimrockmc.com/exhaust-valves-and-servo-motors-explained/

[Michiganr80rt]

2 hours ago, Randyjaco said:

I just ground the butterfly off its axel. No negative effects to performance. My servo/axel still work, but when they stop, I'll go with the eliminator. The flapper is just useless crap.

That is my likely route whether it is a stuck valve or a bad motor. The easiest case is that the valve is stuck open and I just unplug the motor and plug in the eliminator. 

[Michiganr80rt]

4 hours ago, dirtrider said:

Afternoon  Michiganr80rt

 

You might start by verifying the flapper valve is not stuck (that it can turn), if it is frozen up then you can possible address that with lubrication.  

 

If the valve is stuck it can force the motor to draw higher amps. 

 

From the S100RR board, it looks like:

21F502,:,Exhaust,flap,servomotor,,open,circuit

21FA20,:,Exhaust,flap,servomotor,,implausible,signal,or,value

21F500,:,Exhaust,flap,servomotor,,short,circuit,to,ground

I suppose it could be an over current on the loaded motor but more likely a bad motor. I'll know more when I get the bike on the lift. 

This also shows me that the GS-911 provides a more descriptive summary of the fault than MotoScan does.

[Michiganr80rt]

I removed the exhaust. The flap is wide open. I can wiggle the flap so it appears it is not seized. Tomorrow I will disconnect the cables so I can confirm the flap motion. When I turn on  the key the cables do not move so either the servo motor is stuck or it is not getting a command to move. It is looking like a Servo Buddy may be the easiest solution.

 

[Stiggy]

I'm curious as to how this all works out for you (and the bike's performance. ) Better, worse or the same?

It would seem that $69.95 is a pretty reasonable fix.

[gary45]

I do not like the exhaust being noisier at idle but after freeing up the flap a couple of times switched to servo buddy, there is no difference in performance, after having the very quiet K1200LT and K1600GTL I prefer less noise

[Michiganr80rt]

13 hours ago, Stiggy said:

I'm curious as to how this all works out for you (and the bike's performance. ) Better, worse or the same?

It would seem that $69.95 is a pretty reasonable fix.

I removed the motor, the flap moves easily and the spring holds it at wide open. The local BMW dealer checked and the dealer ordering site says there is one motor in the USA which probably means no motor available. I ordered the Servo Buddy.  If I decide I do not like the noise at idle I can always order a motor later.

[Michiganr80rt]

As a follow-up, while I was troubleshooting last week the servo decided to work for a little while and I remembered the flap noise at startup as something that used to happen. Then the check engine light came back on again. It is possible that the servo has not been working for a while. 

 

I installed the Servo Buddy, verified that the flap was in the wide open position, and cleared the flap servo codes from the Engine Control System. The check engine light is now staying off. I do not notice any change in the exhaust volume or performance.