Buffer Air Check Valve Fail closed

TASK 75-26-00-810-817-A
Buffer Air Check Valve Fail closed

1. Possible Causes

CHECK VALVE-LP BUFFER AIR [4051EM]
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 75-26-03-000-801	Removal of the Buffer Air Check Valve
AMM 75-26-03-400-801	Installation of the Buffer Air Check Valve
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
Buffer Air Valve Pressure Sensor Wiring Harness

3. Fault Confirmation
Subtask 75-26-00-710-081-A ** ON A/C NOT FOR ALL

A. Test (for EEC software FCS 4.0 and subsequent (Post PW SB C-73-00-0015A))
(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).

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 75-26-00-810-066-A ** ON A/C NOT FOR ALL

A. Do the steps that follow (for EEC software FCS 4.0 and subsequent(Post PW SB C-73-00-0015A and subsequent)):
(1) If maintenance message ENG1D-0241-BUFFER AIR CHECK VLV FAIL CLSD or ENG2D-0241-BUFFER AIR CHECK VLV FAIL CLSD does not come back, return the engine to service.
(a) Monitor the engine for reoccurring fault message.
(2) If maintenance message ENG1D-0241-BUFFER AIR CHECK VLV FAIL CLSD or ENG2D-0241-BUFFER AIR CHECK VLV FAIL CLSD 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-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 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.
(5) If no problems are found or the fault continues:
(a) Replace CHECK VALVE-LP BUFFER AIR [4051EM] AMM 75-26-03-000-801 and AMM 75-26-03-400-801.
(b) Do the Repair Confirmation. Refer to the Para. 3.
(6) 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.
(7) 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.
(8) 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 75-26-00-710-082-A ** ON A/C NOT FOR ALL

DELETED

5. Close-up
Subtask 75-26-00-860-052-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 04:37:19 UTC