PHMU N2 Speed Sensor Failure on Channel A

TASK 77-31-00-810-804-A
PHMU N2 Speed Sensor Failure on Channel A

1. Possible Causes

HARNESS-FAN, WF02 [4218KS]
PROGNOSTICS AND HEALTH MANAGEMENT UNIT [4609KS]
[4000KS]

2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	MULTIMETER - STANDARD
No specific	1	PLIERS - JAWED, SOFT

B. 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 70-70-00-910-803	SPOP 6 - Cleaning of the Contact Points and Wiring Harnesses
AMM 73-21-00-710-807	Test No.6 - EEC Operation Test (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 73-21-62-000-802	Removal of the EEC Wiring Harness (WF02)
AMM 73-21-62-400-802	Installation of the EEC Wiring Harness (WF02)
AMM 77-31-01-000-801	Removal of the Prognostics and Health Management Unit (PHMU)
AMM 77-31-01-400-801	Installation of the Prognostics and Health Management Unit (PHMU)
AMM 78-36-00-010-802	Opening of the Thrust Reverser Cowl-Doors
AMM 78-36-00-410-802	Closing of the Thrust Reverser Cowl-Doors
EEC and PHMU Wiring Harnesses
PHMU Wiring Schematic

3. Fault Confirmation
Subtask 77-31-00-710-053-A ** ON A/C NOT FOR ALL

A. Do an engine run to idle and shutdown AMM 73-21-00-710-807. Look at the ground scanning report to confirm this fault.

NOTE: The Prognostics and Health Management Unit (PHMU) has reported that the N2 (high rotor speed) analog input circuit from the Electronic Engine Control (EEC) has failed in channel A. The PHMU is located at the 2 o'clock position on the fan case adjacent to the EEC.

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).

(1) If the maintenance message does not come back, examine the harness and electrical connectors as described in the component and harness intermittent fault isolation procedure (Ref. TSM TASK 71-00-00-810-835).
(a) If no problems are found, return the engine to service. Monitor the engine for reoccurring maintenance message.
(2) If the maintenance message comes back (hard fault), go to the Para. Fault Isolation.

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 77-31-00-810-053-A ** ON A/C NOT FOR ALL

A. If there is confirmation of the fault:
(1) Open the thrust reverser cowl-doors AMM 78-36-00-010-802.
(2) Examine the WF02 (4218KS) harness, connector P1 (4000KS-P1) - EEC (4000KS) and connector P9 (4609KS-P9) - PHMU (4609KS), for problems which are possible between the EEC (4000KS) and the PHMU (4609KS).
(a) Inspect for harness damage.
(b) Inspect for loose or damaged connectors.

NOTE: Loose connectors must be disconnected and examined for further wear or damage.

(c) If a problem is found with the harness or connectors:
1 Replace HARNESS-FAN, WF02 [4218KS] AMM 73-21-62-000-802 and AMM 73-21-62-400-802.
2 Do the test given in Para. 3.
(3) If no problems are found with the harness or the fault continue, use a PLIERS - JAWED, SOFT to disconnect the electrical connector P1 (4000KS-P1) from the EEC (4000KS) and connector P9 (4609KS-P9) from the PHMU (4609KS).
(a) Examine the pins and sockets (contacts) for alignment and damage. Look for contacts pushed rearward into the connector face. Replace parts as necessary.
(b) Clean the contacts with contact cleaner and clean cloth per SPOP 6. Blow dry with air (at less than 30 psi) across the connector face AMM 70-70-00-910-803.
(c) Reconnect the electrical connector P1 (4000KS-P1) to the EEC (4000KS), and connector P9 (4609KS-P9) to the PHMU (4609KS).
(d) Do the test given in Para. 3.
(4) If the fault continues:
(a) Disconnect the electrical connector P1 (4000KS-P1) from the EEC (4000KS) and connector P9 (4609KS-P9) from the PHMU (4609KS). Use a MULTIMETER - STANDARD to test the PHMU (4609KS) N1 analog input circuit in the harness. Refer to Table 1. Look for:
1 Wire-to-wire shorts
2 Shorts to ground
3 Continuity (less than 5 ohms resistance).

NOTE: A short to ground is found when the resistance is less than 100 000 (100K) ohms.

Table 1: EEC to PHMU N2 Analog Input Channel A Connector Contacts

WF02 (4218KS) Harness P1(4000KS-P1) EEC (4000KS) Connector Contacts	WF02 (4218KS) Harness P9(4609KS-P9) PHMU (4609KS) Connector Contacts
FF	T
NN	S

(b) If a problem is found with the harness or connectors:
1 Replace HARNESS-FAN, WF02 [4218KS] AMM 73-21-62-000-802 and AMM 73-21-62-400-802.
2 Do the test given in Para. 3.
(5) If no problems are found with the harness or the fault continues:
(a) Replace PROGNOSTICS AND HEALTH MANAGEMENT UNIT [4609KS] AMM 77-31-01-000-801 and AMM 77-31-01-400-801.
(b) Do the test given in Para. 3.
(6) If the fault continues:
(a) Replace [4000KS] AMM 73-21-01-000-801 and AMM 73-21-01-400-801.
(b) Do the test given in Para. 3.

5. Close-up
Subtask 77-31-00-860-053-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 04:37:57 UTC