Buffer Air Shutoff Valve Fail Open

TASK 75-26-00-810-819-A
Buffer Air Shutoff Valve Fail Open

1. Possible Causes

BUFFER AIR VALVE SOLENOID [4056KS]
VALVE-BUFFER AIR [4101JM]
BUFFER AIR VALVE PRESSURE SENSOR [4057KS]
P2.5, T2.5 PROBE [4083KS]
[4000KS]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 71-00-00-810-834-A	General Troubleshooting Guidelines for Additional Troubleshooting Information
TSM TASK 71-00-00-810-835-A	Component and Harness Intermittent Troubleshooting Procedure for Guidance Troubleshooting Intermittent Faults
AMM 71-00-00-720-816	Test No. 17 - Above Idle Test
AMM 73-21-01-000-801	Removal of the Electronic Engine Control (EEC)
AMM 73-21-01-400-801	Installation of the Electronic Engine Control (EEC)
AMM 73-21-22-000-801	Removal of the P2.5/T2.5 Probe
AMM 73-21-22-400-801	Installation of the P2.5/T2.5 Probe
AMM 75-00-00-210-802	Visual Examination of the Engine Air Systems
AMM 75-26-02-000-801	Removal of the LPC Buffer Air Valve
AMM 75-26-02-400-801	Installation of the LPC Buffer Air Valve
AMM 75-26-04-000-801	Removal of the Buffer Air Valve Solenoid
AMM 75-26-04-400-801	Installation of the Buffer Air Valve Solenoid
AMM 75-26-22-000-801	Removal of the Buffer Air Valve Pressure Sensor
AMM 75-26-22-400-801	Installation of the Buffer Air Valve Pressure Sensor
AMM 78-36-00-410-802	Closing of the Thrust Reverser Cowl-Doors
EEC Wiring Harnesses
Buffer Air Valve Solenoid
Buffer Air Valve

3. Fault Confirmation
Subtask 75-26-00-710-085-B ** ON A/C NOT FOR ALL

A. Test (for EEC software FCS 4.0b and subsequent (Post PW SB C-73-00-0017A))
(1) Do an engine run to 80 percent N1 and look at the post flight report to confirm this fault. Refer to AMM 71-00-00-720-816.

NOTE: The Electronic Engine Control (EEC) has reported that the buffer air valve pressure sensor circuit for channel A and B has detected that the buffer air valve has failed in the closed position. The buffer air valve is on the high pressure compressor, located at the 2 o'clock position.

Refer to the general troubleshooting guidelines for additional troubleshooting information (Ref. TSM TASK 71-00-00-810-834).
Refer to the component and harness intermittent troubleshooting procedure for guidance troubleshooting intermittent faults (Ref. TSM TASK 71-00-00-810-835).

Subtask 75-26-00-710-085-A ** ON A/C NOT FOR ALL

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4. Fault Isolation

WARNING: BE CAREFUL WHEN YOU DO WORK ON THE ENGINE AFTER SHUTDOWN. THE ENGINE CAN STAY HOT FOR A LONG TIME. IF YOU DO NOT OBEY THIS WARNING, INJURY CAN OCCUR.

WARNING: REFER TO THE MSDS FOR ALL MATERIAL USED AND THE MANUFACTURER'S SAFETY INSTRUCTIONS FOR ALL EQUIPMENT USED. IF YOU DO NOT OBEY THIS WARNING, INJURY CAN OCCUR.

CAUTION: MAKE SURE YOU REMOVE ELECTRICAL POWER FROM THE EEC BEFORE YOU REMOVE THE ELECTRICAL CONNECTORS. IF YOU DO NOT OBEY THIS INSTRUCTION, DAMAGE TO THE EEC CAN OCCUR.

Subtask 75-26-00-810-068-B ** ON A/C NOT FOR ALL

A. Do the steps that follow (for EEC software FCS 4.0b and subsequent (Post PW SB C-73-00-0017A)):
(1) If maintenance message ENG1D-0237-BUFFER AIR SHUTOFF VLV FAIL OPEN or ENG2D- 0237-BUFFER AIR SHUTOFF VLV FAIL OPEN iENG2D-0237-BUFFER AIR SHUTOFF VLV FAIL OPEN does not come back, return the engine to service.
(a) Monitor the engine for reoccurring fault message
(2) If maintenance message ENG1D-0237-BUFFER AIR SHUTOFF VLV FAIL OPEN or ENG2D- 0237-BUFFER AIR SHUTOFF VLV FAIL OPEN comes back (Hard Fault), do a check of the PFR and SMR to determine if the following maintenance message were set in the same flight leg.

ENGXA-0265-BASOV SOV ELEC FAIL
ENGXB-0266-BASOV SOV ELEC FAIL
ENGXA-0645-BUFFER AIR PRESS SNSR ELEC FAIL
ENGXB-0646-BUFFER AIR PRESS SNSR ELEC FAIL
ENGXD-0647-BUFFER AIR PRES SNSR SIG DISAGREE
ENGXA-0491-P25 SNSR FAIL

(a) If no problems are found or the fault continues, continue with the next step.
(3) If no faults are found or the fault continues, Visually examine the engine bearing cooling system AMM 75-00-00-210-802.
(a) Repair any problems found
1 Do the Repair Confirmation. Refer to the Para. 3
(4) Do an inspection of the Air Supply Tube (AA25) between the Buffer Air Valve Solenoid (4056KS) and the Buffer Air Valve (4101JM) for conditions which could block airflow.
(a) Look for dents and loose connections.
(b) Repair any problems found.
1 Do the Repair Confirmation. Refer to the Para. 3
(5) Do an inspection of the Buffer Air Pressure Sense Line (AS41) between the Buffer Air Valve (4101JM) and the Buffer Air Valve Pressure Sensor (4057KS) for conditions which could block airflow.
(a) Look for dents and loose connections.
(b) Repair any problems found.
1 Do the Repair Confirmation. Refer to the Para. 3
(c) If no problems are found or the fault continues, continue with the next step
(6) If the fault continues:
(a) Replace BUFFER AIR VALVE SOLENOID [4056KS] AMM 75-26-04-000-801 and AMM 75-26-04-400-801.
(b) Do the repair confirmation. Refer to the Para. 3
(7) If the fault continues:
(a) Replace VALVE-BUFFER AIR [4101JM] AMM 75-26-02-000-801 and AMM 75-26-02-400-801.
(b) Do the repair confirmation. Refer to the Para. 3.
(8) If the fault continues:
(a) Replace BUFFER AIR VALVE PRESSURE SENSOR [4057KS] AMM 75-26-22-000-801 and AMM 75-26-22-400-801.
(b) Do the repair confirmation. Refer to the Para. 3.
(9) If the fault continues:
(a) Replace P2.5, T2.5 PROBE [4083KS] AMM 73-21-22-000-801 and AMM 73-21-22-400-801.
(b) Do the repair confirmation. Refer to the Para. 3.
(10) If the fault continues:
(a) Replace [4000KS] AMM 73-21-01-000-801 and AMM 73-21-01-400-801.
(b) Do the repair confirmation. Refer to the Para. 3.

Subtask 75-26-00-810-068-A ** ON A/C NOT FOR ALL

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Subtask 75-26-00-710-086-A ** ON A/C NOT FOR ALL

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5. Close-up
Subtask 75-26-00-860-054-A ** ON A/C NOT FOR ALL

A. Put the aircraft back to its initial configuration.
(1) Make sure that the work area is clean and clear of tools and other items.
(a) Close the thrust reverser cowl-doors AMM 78-36-00-410-802.

[Rev.8 from Aug 2018] 2026.04.04 04:40:45 UTC