Failure of the TBV valve on Engine 1

TASK 75-26-00-810-810-A
Failure of the TBV valve on Engine 1

1. Possible Causes

ECU [4000KS]
Transient Bleed Valve (TBV)
HMU
harness HJ8

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 73-21-10-000-002	Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-002	Installation of the Hydromechanical Unit (HMU)
AMM 73-21-50-000-041	Removal of the HJ8 Harness for SAC Engines
AMM 73-21-50-210-002	Visual Inspection of the Wiring Harnesses
AMM 73-21-50-400-041	Installation of the HJ8 Harness for SAC Engines
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)
AMM 73-29-00-710-040	Operational Test of the FADEC on the ground (with Engine Motoring)
AMM 75-26-10-000-001	Removal of the Transient Bleed Valve
AMM 75-26-10-400-001	Installation of the Transient Bleed Valve

3. Fault Confirmation
Subtask 75-26-00-710-068-A ** ON A/C NOT FOR ALL

A. Do the operational test of the FADEC 1B on the ground (with engine motoring) AMM 73-29-00-710-040.

4. Fault Isolation
Subtask 75-26-00-810-059-A ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message TBV VLV, HMU:

Disconnect the HJ8 harness fron the J8 receptacle on the ECU (4000KS). Make sure that the electrical contacts of the J8 receptacle are not bent or have not moved AMM 73-21-50-210-002.

(1) If you find damage:

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

(2) Do a resistance check of the TBV valve circuits (channel B) through the HJ8 harness, between:
. pins 20 and 40 (1 to 150 Ohms).
(a) If the resistance values are in the specified limits:

replace the Transient Bleed Valve (TBV) AMM 75-26-10-000-001 and AMM 75-26-10-400-001.

1 If the fault continues:

replace the HMU AMM 73-21-10-000-002 and AMM 73-21-10-400-002.

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

disconnect the harness HJ8 from the HMU and do a check of the resistance of the HMU between:
. pins 20 and 40 (1 to 150 Ohms).

1 If the resistance values are in the specified limits:

replace the defective harness HJ8 AMM 73-21-50-000-041 and AMM 73-21-50-400-041.

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

replace the HMU AMM 73-21-10-000-002 and AMM 73-21-10-400-002.

(3) If the fault continues:

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

Subtask 75-26-00-710-069-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.A.

[Rev.8 from Aug 2018] 2026.04.04 04:37:06 UTC