22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 115 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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.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 not  | msg. no.  | Possible Causes:  |
 | engaged  | 22-21015  | 1. Yaw Damper Engage Switch not engaged during YDC  |
 |  |  | BITE Self Test  |
 |  |  | 2. Yaw Damper Coupler  |
 |  |  | 3. Autopilot Accessory Unit  |
 |  |  | 4. Integrated Flight System Accessory Unit  |
 |  |  |  |
 |  |  | Corrective Action:  |
 |  |  | 1. Perform Yaw Damper Coupler - Adjustment/Test.  |
 |  |  | 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. Do a wiring check between D295 pin 14, and the Yaw |
 |  |  | Damper Engage Switch, and autopilot accessory  |
 |  |  | unit, or integrated flight system accessory unit.  |
 |  |  | 4. Inspect electrical connectors for bent or broken  |
 |  |  | pins, contamination, or damage.  |
 |  |  | 5. If the problem is not corrected, replace the  |
 |  |  | Yaw Damper Engage Switch.  |
 |  |  | 6. If the problem is not corrected, replace the  |
 |  |  | Yaw Damper Coupler (AMM 22-12-31/401).  |
 |  |  | 7. If the problem is not corrected, replace the  |
 |  |  | autopilot accessory unit (AMM 22-11-36/401 or  |
 |  |  | integrated flight system accessory unit  |
 |  |  | (AMM 22-11-37/401).  |

 ................................................................................. | B hyd | msg. no. | Possible Causes: | | not on | 22-21016 | 1. B System Hydraulics not pressurized during YDC | | | | BITE Servo Test | | | | 2. Flight Control System B Pressure Switch | | | | 3. Yaw Damper Coupler | | | | | | | | Corrective Action: | | | | 1. Do a wiring check between D295 pin 7 and D816 | | | | pin 3 at the Flight Control System B Pressure | | | | Switch. | | | | 2. Do a wiring check to ground at D816 pin 2 at the | | | | Flight Control System B Pressure Switch. | | | | 3. Inspect electrical connectors for bent or broken | | | | pins, contamination, or damage. | | | | 4. If the problem is not corrected, replace Flight | | | | Control System B Pressure Switch (AMM 29-34-21/401)| | | | 5. If the problem is not corrected, replace the | | | | Yaw Damper Coupler (AMM 22-12-31/401). |
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 22-12-01
 YAW DAMPER COUPLER  ú ú 02 Page 116 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 actr  | msg. no.  | Possible Causes:  |
 | limit  | 22-21017  | 1. Excessive Yaw Damper Actuator Travel  |
 |  |  | 2. Rudder Power Control Unit  |
 |  |  | 3. Yaw Damper Coupler  |
 |  |  |  |
 |  |  | Corrective Action:  |
 |  |  | 1. Make sure that the resistance between D295 pin 46  |
 |  |  | and D295 pin 47 is 80 ohms.  |
 |  |  | 2. Make sure that the resistance between D295 pin 9  |
 |  |  | and D295 pin 1 is 100 ohms.  |
　
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