Loss of the HMU Control Through Channel B on Engine 1

TASK 73-29-00-810-846-A
Loss of the HMU Control Through Channel B on Engine 1

1. Possible Causes

ECU [4000KS]
harness J8
HMU-1 [4000KC1]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 73-21-10-000-001	Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-001	Installation of the Hydromechanical Unit (HMU)
AMM 73-21-50-000-007	Removal of J8 Harness
AMM 73-21-50-400-007	Installation of the J8 Harness
AMM 73-21-60-000-001	Removal of the Electronic Control Unit (ECU)
AMM 73-21-60-400-001	Installation of the Electronic Control Unit (ECU)
ASM 732518
AMM 73-29-00-710-040	Operational Test of the FADEC on the ground (with Engine Motoring)

3. Fault Confirmation
Subtask 73-29-00-710-108-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the operational test of the FADEC 1B on the ground (with engine motoring) AMM 73-29-00-710-040.
(2) Read the TROUBLE SHOOTING DATA of the FADEC MENU on the MCDU (Ref. 70-00-00, P. Block 301).

4. Fault Isolation
Subtask 73-29-00-810-124-A ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information FMV FEEDBACK SIGNAL:

do a check for open or short to ground at pins J8/16, 17, 18, 34, 35, 36, 37 of the harness J8 from the ECU (4000KS) to the fuel-meter valve-resolver in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 16 and 34 (34 to 46 or 85 to 150 Ohms)
. pins 35 and 36 (21 to 29 or 44 to 76 Ohms)
. pins 18 and 37 (21 to 29 or 44 to 76 Ohms)
. pins 16 and 17 (> 10 Megohms)
. pins 35 and 17 (> 10 Megohms)
. pins 18 and 17 (> 10 Megohms)
. pin 16 and the ground (> 10 Megohms)
. pin 35 and the ground (> 10 Megohms)
. pin 18 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 16 and 34 (34 to 46 or 85 to 150 Ohms)
. pins 35 and 36 (21 to 29 or 44 to 76 Ohms)
. pins 18 and 37 (21 to 29 or 44 to 76 Ohms)
. pins 16 and 17 (> 10 Megohms)
. pins 35 and 17 (> 10 Megohms)
. pins 18 and 17 (> 10 Megohms)
. pin 16 and the ground (> 10 Megohms)
. pin 35 and the ground (> 10 Megohms)
. pin 18 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

NOTE: If the resistance found is in one of the given ranges, you must check the other channel. The difference between the two channels must not be more than 5 Ohms.

Subtask 73-29-00-810-125-A ** ON A/C NOT FOR ALL

B. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information FMV TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/12, 27, 28 of the harness J8 from the ECU (4000KS) to the fuel-meter torque-motor in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 27 and 28 (17 to 23 Ohms)
. pins 27 and 12 (> 10 Megohms)
. pin 27 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 27 and 28 (17 to 23 Ohms)
. pins 27 and 12 (> 10 Megohms)
. pin 27 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-126-A ** ON A/C NOT FOR ALL

C. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information LPT TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/19, 38, 39 of the harness J8 from the ECU (4000KS) to the LPT torque-motor current in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 19 and 38 (17 to 23 Ohms)
. pins 19 and 39 (> 10 Megohms)
. pin 19 and the ground (> 10 Megohms)

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 19 and 38 (17 to 23 Ohms)
. pins 19 and 39 (> 10 Megohms)
. pin 19 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-127-A ** ON A/C NOT FOR ALL

D. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information HPT TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/10, 23, 24 of the harness J8 from the ECU (4000KS) to the HPT torque-motor current in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 23 and 24 (17 to 23 Ohms)
. pins 23 and 10 (> 10 Megohms)
. pin 23 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 23 and 24 (17 to 23 Ohms)
. pins 23 and 10 (> 10 Megohms)
. pin 23 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-128-A ** ON A/C NOT FOR ALL

E. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information BSV SOLENOID CURRENT:

do a check for open or short to ground at pins J8/6, 7, 39 of the harness J8 from the ECU (4000KS) to the BSV solenoid in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 6 and 7 (26 to 36 Ohms)
. pins 6 and 39 (> 10 Megohms)
. pin 6 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 6 and 7 (26 to 36 Ohms)
. pins 6 and 39 (> 10 Megohms)
. pin 6 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-129-A ** ON A/C NOT FOR ALL

F. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information RAC TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/20, 39, 40 of the harness J8 from the ECU (4000KS) to the RACC torque motor in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 20 and 40 (17 to 23 Ohms)
. pins 20 and 39 (> 10 Megohms)
. pin 20 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 20 and 40 (17 to 23 Ohms)
. pins 20 and 39 (> 10 Megohms)
. pin 20 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-130-A ** ON A/C NOT FOR ALL

G. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information VSV TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/10, 25, 26 of the harness J8 from the ECU (4000KS) to thge VSV torque motor in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 25 and 26 (17 to 23 Ohms)
. pins 25 and 10 (> 10 Megohms)
. pin 25 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 25 and 26 (17 to 23 Ohms)
. pins 25 and 10 (> 10 Megohms)
. pin 25 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-810-131-A ** ON A/C NOT FOR ALL

H. If the test gives the maintenance message J8, HMU, ECU and the TROUBLE SHOOTING DATA gives the complementary information VBV TORQUE MOTOR CURRENT:

do a check for open or short to ground at pins J8/13, 29, 30 of the harness J8 from the ECU (4000KS) to the VBV torque motor in the HMU ASM 732518.

(1) If the wiring is not correct:

repair the above wiring.

(2) If the wiring is correct:

disconnect the harness J8 from the ECU and do a check of the ECU cable resistance between:
. pins 29 and 30 (17 to 23 Ohms)
. pins 29 and 13 (> 10 Megohms)
. pin 29 and the ground (> 10 Megohms).

(a) If the resistance values are in the specified limits:

replace the ECU [4000KS] , AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the resistance values are out of the specified limits:

disconnect the harness J8 from the HMU and do a resistance check of the HMU between:
. pins 29 and 30 (17 to 23 Ohms)
. pins 29 and 13 (> 10 Megohms)
. pin 29 and the ground (> 10 Megohms).

1 If the resistance values are in the specified limits:

replace the harness J8 , AMM 73-21-50-000-007 and AMM 73-21-50-400-007.

2 If the resistance values are out of the specified limits:

replace the HMU-1 [4000KC1] AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-29-00-710-109-A ** ON A/C NOT FOR ALL

I. Do the test given in Para. 3.A.(1).

[Rev.8 from Aug 2018] 2026.04.04 04:35:56 UTC