EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH 10-62253 ú
 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 112 ú Jul 12/01 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A 
737-300/400/500MAINTENANCE MANUAL
 ~............................................................................... | FAULT MESSAGE/CORRECTIVE ACTION (TABLE 101) | ................................................................................. | YDC Fault | YDC Fault | Corrective Action | | Message | Detail 1 | | .................................................................................
 | YD sol | msg. no. | Possible Causes:  | 
 | low volt | 22-21011 | 1. Low 28 VDC voltage applied to the Yaw Damper  | 
 |  |  | Coupler  | 
 |  |  | 2. Yaw Damper Engage Switch  | 
 |  |  | 3. Yaw Damper Coupler  | 
 |  |  | 4. Yaw Damper Engage Solenoid  | 
 |  |  |  | 
 |  |  | Corrective Action:  | 
 |  |  | 1. Make sure that the voltage to D295 pin 4 is  | 
 |  |  | between 22.0 and 29.5 volts DC with the Yaw Damper | 
 |  |  | DC circuit breaker closed.  | 
 |  |  | 2. Make sure that the resistance from D295 pin 14 to  | 
 |  |  | ground is less than 2.0 ohms with Yaw Damper  | 
 |  |  | Engage Switch in the OFF position.  | 
 |  |  | 3. Make sure that the resistance from D295 pin 20  | 
 |  |  | to ground is between 50 to 80 ohms.  | 
 |  |  | 4. Do a wiring check between D295 pin 20 and D291  | 
 |  |  | pin 1 at the Yaw Damper Engage Solenoid  | 
 |  |  | (AMM 22-12-21/401).  | 
 |  |  | 5. Do a wiring check to ground from D291 pin 2 at the | 
 |  |  | Yaw Damper Engage Solenoid.  | 
 |  |  | 6. Inspect electrical connectors for bent or broken  | 
 |  |  | pins, contamination, or damage.  | 
 |  |  | 7. If the problem is not corrected, replace the  | 
 |  |  | Yaw Damper Coupler (AMM 22-12-31/401).  | 
 |  |  | 8. If the problem is not corrected, replace the Yaw  | 
 |  |  | Damper Engage Solenoid (AMM 22-12-21/401).  |
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH 10-62253 ú
 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 113 ú Jul 12/01 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A 
737-300/400/500MAINTENANCE MANUAL
 ~............................................................................... | FAULT MESSAGE/CORRECTIVE ACTION (TABLE 101) | ................................................................................. | YDC Fault | YDC Fault | Corrective Action | | Message | Detail 1 | | .................................................................................
 | PR sol  | msg. no.  | Possible Causes:  | 
 | low volt  | 22-21012  | 1. Low 28 VDC voltage applied to the Yaw Damper  | 
 |  |  | Coupler  | 
 |  |  | 2. Pressure Reducer Bypass Valve  | 
 |  |  | 3. Yaw Damper Coupler  | 
 |  |  |  | 
 |  |  | Corrective Action:  | 
 |  |  | 1. Make sure that the voltage to D295 pin 4 is  | 
 |  |  | between 22.0 and 29.5 volts DC with the Yaw Damper | 
 
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