03/15/21
Message Overview:
Message Description:
Both left and right GP-5 busses from the Input/Output concentrator (IOC) non communicating to the PSEU. Verify PSEU, IOC and aircraft wiring.
Possible Causes:
- Proximity-Sensor Electronic Unit (PSEU) (A9)
- Input/Output Concentrator (IOC) (A4-IOC)
- Junction Box 2 (JB2)
- Junction Box 4 (JB4)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin: None
Forum Articles/Infoservice/Newsletter: None
Quick Links:
| Removal of the Junction Box JB1 | AMM 24-63-01-000-802 |
| Installation of the Junction Box JB1 | AMM 24-63-01-400-802 |
| Removal of the Input/Output Concentrator Unit (IOC) | AMM 31-45-05-000-801 |
| Installation of the Input/Output Concentrator Unit (IOC) | AMM 31-45-05-400-801 |
| Removal of the Proximity-Sensor Electronic Unit (PSEU) | AMM 32-61-09-000-801 |
| Installation of the Proximity-Sensor Electronic Unit (PSEU) | AMM 32-61-09-400-801 |
| Functional Test of the Proximity-Sensor Electronic Unit (PSEU) | AMM 32-61-09-720-801 |
| Wiring - Maintenance Practices - ALL | SPM 20-12-00-02 |
| Wire Repair - Maintenance Practices - ALL | SPM 20-12-10-02 |
| Electrical Connectors - Maintenance Practice - ALL | SPM 20-20-00-02 |
Troubleshooting Recommendations:
- Pull and reset the PSEU gear system breakers (CB1-C13, CB1-C14, CB2-C13, CB2-C14), recheck the system for the fault.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Reset the circuit breakers R IAPS CB CB2-B6, L IAPS CB CB1-B6, then look for other failures related to the IOCs, swap the IOCs.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Check the ARINC 429 data bus from the PSEU A9AP1 PINS 10G, 9G through Junction Box 4 to IAPS A4P101 PINS 1, 2. Repair as required.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Check the ARINC 429 data bus from the PSEU A9AP1 PINS 10G, 9G through Junction Box 4 to DCU A14EP1 PINS 1A, 1B. Repair as required.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Check the ARINC 429 data bus from the PSEU A9CP1 PINS 1D, 2D through Junction Box 2 to IAPS A4P1 PINS 1, 2. Repair as required.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Check the ARINC 429 data bus from the PSEU A9CP1 PINS 1D, 2D through Junction Box 2 to DCU A14DP1 PINS 5A, 5B. Repair as required.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Replace JB4 and JB2.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Replace the PSEU.
- Functional Test of the Proximity Sensor Electronic Unit (PSEU).


