Thrust-Reverser HCU Pressure-Switch Feedback Disagree on Engine 1

TASK 78-31-00-810-821-A
Thrust-Reverser HCU Pressure-Switch Feedback Disagree on Engine 1

1. Possible Causes

PRESS SW-HCU [4102KS]
harness J5
harness J6
thrust reverser harness
junction box
ECU [4000KS]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 71-51-43-000-049	Removal of the ECU (Channel A) to Thrust Reverser Junction Box Harnesses
AMM 71-51-43-400-049	Installation of the ECU (Channel A) to Thrust Reverser Junction Box Harnesses
AMM 71-51-44-000-002	Removal of the Thrust Reverser Harness 238W0908
AMM 71-51-44-400-002	Installation of the Thrust Reverser Harness 238W0908
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 732516
AMM 78-31-00-710-040	Operational Test of the Thrust Reverser System
AMM 78-31-00-710-042	Operational Test of the Thrust Reverser System
AMM 78-31-16-000-040	Removal of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-000-041	Removal of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-400-040	Installation of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-400-041	Installation of the Hydraulic Control Unit Pressure Switch

3. Fault Confirmation
Subtask 78-31-00-710-090-A ** ON A/C NOT FOR ALL

A. Do an operational test of the thrust reverser system AMM 78-31-00-710-040.

Subtask 78-31-00-710-090-B ** ON A/C NOT FOR ALL

A. Do an operational test of the thrust reverser system AMM 78-31-00-710-042.

4. Fault Isolation
Subtask 78-31-00-810-070-B ** ON A/C NOT FOR ALL

A. This fault message is generated if there is a disagreement between channel A and channel B on the HCU pressure switch output signal.
(1) If the test gives the maintenance message TR PR SW, J5/J6, ECU:

Get access to the HCU,
Disconnect the connector A on the HCU pressure switch (4102KS),
Install jumper wires between pins 2 and 3 on harness connector A of the HCU pressure switch (4102KS) and between pins 4 and 5 on harness connector A of the HCU pressure switch (4102KS),
Disconnect the harnesses J5 and J6 from the ECU (4000KS) and do a resistance check at each harness connector to the ECU ASM 732516 between:
. Pins 12 and 13 (<5 ohms)
. Pins 12 and 11 (>10 megohms)
. Pin 12 and the ground (>10 megohms).

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

Replace the PRESS SW-HCU [4102KS] AMM 78-31-16-000-040 and AMM 78-31-16-400-040.

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

Do a continuity and insulation check of the harnesses between the ECU and the HCU pressure switch,
Repair or replace the defective harness J5 or harness J6 or thrust reverser harness or junction box AMM 71-51-44-000-002 and AMM 71-51-44-400-002.

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

(2) If the test does not give the maintenance message TR PR SW, J5/J6, ECU; this is indicative of an intermittent fault that may be caused by defective electrical contacts in the harnesses and junction box between the ECU and the HCU:

Do a check of the harnesses J5 and J6 and the thrust reverser harnesses and the junction box between the ECU and the HCU for correct condition,
Do a check of the connectors for looseness, bent pins, corrosion or contamination.

(a) If damage is found:

Clean, repair or replace as required AMM 71-51-44-000-002 and AMM 71-51-44-400-002.

(b) If no damage is found and fault continues while maintenance message is never confirmed during the test:

Replace the PRESS SW-HCU (4102KS) AMM 78-31-16-000-040 and AMM 78-31-16-400-040.

Repair or replace the defective harnesses J5 or J6 or thrust reverser harness AMM 71-51-44-000-002 and AMM 71-51-44-400-002.

(d) If the fault continues:

Replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

Subtask 78-31-00-810-070-C ** ON A/C NOT FOR ALL

Get access to the HCU,
Disconnect the connector A on the HCU pressure switch (4102KS),
Install jumper wires between pins 2 and 3 on harness connector A of the HCU pressure switch (4102KS) and between pins 4 and 5 on harness connector A of the HCU pressure switch (4102KS),
Disconnect the harnesses J5 and J6 from the ECU (4000KS) and do a resistance check at each harness connector to the ECU ASM 732516 between:
. Pins 12 and 13 (<5 ohms)
. Pins 12 and 11 (>10 megohms)
. Pin 12 and the ground (>10 megohms).

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

Replace the PRESS SW-HCU [4102KS] AMM 78-31-16-000-041 and AMM 78-31-16-400-041.

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

Do a continuity and insulation check of the harnesses between the ECU and the HCU pressure switch,
Repair or replace the defective harness J5 or harness J6 or thrust reverser harness or junction box AMM 71-51-43-000-049 and AMM 71-51-43-400-049.

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

Do a check of the harnesses J5 and J6 and the thrust reverser harnesses and the junction box between the ECU and the HCU for correct condition,
Do a check of the connectors for looseness, bent pins, corrosion or contamination.

(a) If damage is found:

Clean, repair or replace as required AMM 71-51-43-000-049 and AMM 71-51-43-400-049.

(b) If no damage is found and fault continues while maintenance message is never confirmed during the test:

replace the PRESS SW-HCU (4102KS) AMM 78-31-16-000-041 and AMM 78-31-16-400-041.

Repair or replace the defective harnesses J5 or J6 or thrust reverser harness AMM 71-51-43-000-049 and AMM 71-51-43-400-049.

(d) If the fault continues:

Replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

Subtask 78-31-00-710-091-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.A.
(1) No additional maintenance action is required if the fault is not confirmed.
(2) Repeat the fault isolation procedure if the fault continues.

[Rev.8 from Aug 2018] 2026.04.04 04:37:59 UTC