Loss of the feedback signal from the TBV valve through the channel B on Engine 2

TASK 75-26-00-810-804-A
Loss of the feedback signal from the TBV valve through the channel B on Engine 2

1. Possible Causes

ECU [4000KS]
harness HJ12
harness CJ12L
Transient Bleed Valve (TBV)

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 73-21-50-000-027	Removal of the CJ12L Harness
AMM 73-21-50-000-045	Removal of the HJ12 Harness for SAC Engines
AMM 73-21-50-400-027	Installation of the CJ12L Harness
AMM 73-21-50-400-045	Installation of the HJ12 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 75-26-00-710-056-A ** ON A/C NOT FOR ALL

A. Do the operational test of the FADEC 2B on the ground (with engine non motoring) AMM 73-29-00-710-040.

4. Fault Isolation
Subtask 75-26-00-810-053-A ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message TBV VLV, J12, ECU:

disconnect the HJ12 harness from the J12 receptacle on the ECU (4000KS). Make sure that the electrical contacts of the J12 receptacle are not bent or have not moved.

(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 HJ12 and CJ12L harnesses, between:
. pins 40 and 41 (1 to 150 Ohms)
. pins 20 and 39 (1 to 150 Ohms)
. pins 8 and 22 (1 to 150 Ohms)
. pins 40 and 21 (more than 10 Megohms)
. pins 20 and 21 (more than 10 Megohms)
. pins 8 and 21 (more than 10 Megohms)
. pin 40 and the ground (more than 10 Megohms)
. pin 20 and the ground (more than 10 Megohms)
. pin 8 and the ground (more than 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 cable HJ12 from the cable CJ12L at the 6 o'clock junction box and do a resistance check of the TBV valve circuits (channel B), through the CJ12L harness between:
. pins 2 and 3 (1 to 150 Ohms)
. pins 4 and 5 (1 to 150 Ohms)
. pins 12 and 13 (1 to 150 Ohms)
. pins 2 and 1 (more than 10 Megohms)
. pins 4 and 1 (more than 10 Megohms)
. pins 12 and 1 (more than 10 Megohms)
. pin 2 and ground (more than 10 Megohms)
. pin 4 and ground (more than 10 Megohms)
. pin 12 and ground (more than 10 Megohms)

1 If the resistance values are in the specified limits:

replace the harness HJ12 AMM 73-21-50-000-045 and AMM 73-21-50-400-045.

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

disconnect the CJ12L harness from the TBV valve and do a resistance check of the TBV valve circuits (channel B) between:
. pins 2 and 3 (1 to 150 Ohms)
. pins 4 and 5 (1 to 150 Ohms)
. pins 6 and 7 (1 to 150 Ohms)
. pin 2 and ground (more than 10 Megohms)
. pin 4 and ground (more than 10 Megohms)
. pin 6 and ground (more than 10 Megohms).

a If the resistance values are in the specified limits:

replace the harness CJ12L AMM 73-21-50-000-027 and AMM 73-21-50-400-027.

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

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

(3) Connect the disconnected harnesses.

Subtask 75-26-00-710-057-A ** ON A/C NOT FOR ALL

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

[Rev.8 from Aug 2018] 2026.04.04 04:37:05 UTC