Message Name:

FUEL SYSTEM HMU 1A

Message Code:

B3-303010

Associated CAS:

L ENGINE MINOR FAULT
(Advisory)

Left engine fuel system HMU fault 1A.

[MCID 0110]
Fuel system HMU 1A.
An open-type fault in the HMU sensors/effectors circuit was sensed. This circuit includes the HMU sensors/effectors, the electronic control unit (ECU) A and the wires between them. The ECU A cannot support full-system operation.

• Hydromechanical Unit (HMU) (Channel A connection)
• Wiring Harness (W4)
• Full Authority Digital Engine Control Unit (FADEC) Electronic Control Unit A (ECU) (A41)

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

• If the L or R ENG MINOR FAULT CAS message is shown with this fault, this is a Short Term dispatch (STD) fault and is subject to correction outlined in the Honeywell LEMM SUB TASK 5-10-00-200-003.
• If a L or R FADEC FAIL CAS message is shown, this is a No Dispatch (ND) fault and is subject to correction outlined in the Honeywell LEMM SUB TASK 5-10-00-200-003.
• Check for the following MDC messages displayed with the fault: X-channel bus 1A (MCID 0905), X-channel bus 1B (MCID 0906), X-channel discrete 1A (MCID 0933), X-channel discrete 1B (MCID 0934). If any of the above MCID codes are posted, correct the cross channel faults first.

Issues with the N1 shut-off (Broken Shaft Connector), or bleed surge valves, contact Honeywell FSR and find out about status of Dash 12 W5 harness. Ref Honeywell S/B AS907-76-9011. Most likely tied to connector pin friction or loose connector.

1. MCID 0110 fault only is present, troubleshoot using the following steps for aircraft and engine fault isolation with reference to the Light Engine Maintenance Manual TASK 72-00-00-810-009.
2. Reset and reboot the ECU to recheck the MDC MCID for the posted fault.
3. Remove the connector on the ECU 1A W4P13, inspect for burned or pushed back pins/sockets, then check the following segments per the table, repair wiring if required per the wiring manual standard practices.
   

   From	To	Value
   W4P13 Pin 43	W4P13 Pin 44	9 to 50 Ω
   W4P13 Pin 51	W4P13 Pin 52	18 to 100 Ω
   W4P13 Pin 36	W4P13 Pin 37	200 to 900 Ω
   W4P13 Pin 23	W4P13 Pin 30	50 to 250 Ω
   W4P13 Pin 24	W4P13 Pin 30	50 to 250 Ω
   W4P13 Pin 42	W4P13 Pin 34	4 to 30 Ω
   W4P13 Pin 21	W4P13 Pin 35	120 to 500 Ω

4. If the resistance values check good, proceed to step 7, if the resistance values were bad at the ECU, perform a resistance check on the HMU as shown in the table below:

   From	To	Value
   W4J14 Pin 12	W4J14 Pin 11	9 to 50 Ω
   W4J14 Pin 6	W4J14 Pin 7	18 to 100 Ω
   W4J14 Pin 2	W4J14 Pin 1	200 to 900 Ω
   W4J14 Pin 8	W4J14 Pin 9	50 to 250 Ω
   W4J14 Pin 10	W4J14 Pin 9	50 to 250 Ω
   W4J14 Pin 4	W4J14 Pin 5	4 to 30 Ω
   W4J14 Pin 21	W4J14 Pin 35	120 to 500 Ω

5. If the resistance values fail, replace the HMU, if the resistance values check good, suspect the W4 wiring harness and replace per the Honeywell LEMM TASK 76-10-01-050-801.
6. Do a short to ground check as shown in the table below:
   

   From	To	Value
   W4P13 Pin 43	Ground	> 5,000 Ω
   W4P13 Pin 37	Ground	> 5,000 Ω
   W4P13 Pin 51	Ground	> 5,000 Ω

7. If the resistance values check good, proceed to step 10, if the resistance values were bad at the ECU, perform a resistance check on the HMU as shown in the table below:
   

   From	To	Value
   W4J14 Pin 12	Ground	> 5,000 Ω
   W4J14 Pin 2	Ground	> 5,000 Ω
   W4J14 Pin 6	Ground	> 5,000 Ω

8. If the resistance values check good, proceed to step 10, if the resistance values are bad, replace the HMU IAW AMM TASK 73-20-01-000-801, TASK 73-20-01-400-801.
9. Consider swapping or replacing the A channel ECUs for the left engine, remove and replace IAW AMM TASK 76-10-05-000-801, TASK 76-10-05-400-801 then recheck the system for the fault.