Center Tank Low Level Sensor 21QJ

TASK 28-46-00-810-806-A
Center Tank Low Level Sensor 21QJ

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.

1. Possible Causes

FLSCU-1 [7QJ]
aircraft wiring
HARNESS-CHAN A, CTR TK [17QT]
SENSOR-LOW LVL, L CTR TK CHANNEL A [21QJ]
fused adaptor at 7509VC

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

REFERENCE	QTY	DESIGNATION
No specific	AR	MULTIMETER - STANDARD

B. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 28-46-00-810-818-A	FLSCU1(2) 7QJ(9QJ)
ESPM 2053210
AMM 28-10-00-910-001	Safety Procedures When You Do Work in a Fuel Tank
AMM 28-10-00-910-002	Access to the Fuel Tanks and the Work Areas
AWM 282107
AWM 282603
AMM 28-42-44-000-001	Removal of the Center Tank Harness
AMM 28-42-44-400-001	Installation of the Center Tank Harness
AMM 28-46-00-740-001	Functional (BITE) Test
ASM 284603
AWM 284606
AWM 284609
AMM 28-46-15-000-004	Removal of the Center-Tank Fuel-Level Sensors
AMM 28-46-15-400-012	Installation of the Center-Tank Fuel-Level Sensors
AMM 28-46-34-000-001	Removal of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 28-46-34-400-001	Installation of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 32-12-00-010-001	Open the Main Gear Doors for Access

3. Fault Confirmation
Subtask 28-46-00-865-071-A

A. Table of the circuit breakers referred to in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	FUEL/CTR TK/PUMPS1 AND 2/CTL AND IND	31QA	R25
** ON A/C NOT FOR ALL
121VU	FUEL/CTR TK/L&R XFR/CTL & IND	1QL	R25

Subtask 28-46-00-740-055-B ** ON A/C NOT FOR ALL

B. Test
(1) Do the BITE test of the FLSS AMM 28-46-00-740-001.

NOTE: The 28VDC power supply for the FLSCU-1 (7QJ) low level channel 21QJ/(LS6) is from the C/B-31QA.

(2) Examine the FLSS STATUS page on the MCDU.
(3) If a fault message(s) for one or more of the other FLSS sensors and/or the FLSCU-1 (7QJ) is shown:

do (Ref. TSM TASK 28-46-00-810-818).

(4) If the message 284615 C LO LEVEL SENSOR 21QJ:

is shown, do Para. 4.A.
is not shown, no work steps are necessary.

NOTE: You can get more data from the:

Aircraft Maintenance Manual (AMM) Chap. 28-46-00, the Fuel Level Sensing System, Description and Operation (D and O)
Trouble Shooting Manual (TSM) - Task Supporting Data (Ref. P. Block 301)
Aircraft Schematic Manual (ASM) ASM 284603.

You can get more Trouble-shooting data from the CFDS(FUEL):

Input Parameters Page 3 (Ref. P. Block 301), used with the Fuel Level Sensors Operating (Changeover) Values (Ref. P. Block 301)
FLSCU Trouble-shooting Data (Ref. P. Block 301).

NOTE: OPTIONAL TESTING:
Where a PSD A320-2 Fuel Level Sensing Test Set is available measurements can be taken before a decision is made to go into or close up a fuel tank. The Test Set enables the tank mounted components and tank wiring to be tested from the tank wall connectors.

Subtask 28-46-00-740-055-C ** ON A/C NOT FOR ALL

B. Test
(1) Do the BITE test of the FLSS AMM 28-46-00-740-001.

NOTE: The 28VDC power supply for the FLSCU-1 (7QJ) low level channel 21QJ/(LS6) is from the C/B-1QL.

(2) Examine the FLSS STATUS page on the MCDU:
(3) If a fault message(s) for one or more of the other FLSS sensors and/or the FLSCU-1 (7QJ) is shown:

do (Ref. TSM TASK 28-46-00-810-818).

(4) If the message 284615 C LO LEVEL SENSOR 21QJ:

is shown, do Para. 4.A.
is not shown: no work steps are necessary.

NOTE: You can get more data from the:

Aircraft Maintenance Manual (AMM) Chap. 28-46-00, the Fuel Level Sensing System, Description and Operation (D and O)
Trouble Shooting Manual (TSM) - Task Supporting Data (Ref. P. Block 301)
Aircraft Schematic Manual (ASM) ASM 284603.

You can get more Trouble-shooting data from the CFDS(FUEL):

Input Parameters Page 3 (Ref. P. Block 301), used with the Fuel Level Sensors Operating (Changeover) Values (Ref. P. Block 301)
Trouble-shooting Data (Ref. P. Block 301).

NOTE: OPTIONAL TESTING:
Where a PSDA321-1 Test Set is available, a check can be made before a decision is made to go into or close up a fuel tank. The Test Set enables a GO/NOGO check to be made of the tank mounted components and wiring from the tank wall connectors.

4. Fault Isolation
Subtask 28-46-00-810-055-C ** ON A/C NOT FOR ALL

A. Procedure
(1) Do the steps applicable to the test equipment available.
(2) Test Equipment

(a) If there is:

approved test equipment available, go to Step (3)
no approved test equipment available, go to Step (6).

(3) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
(4) Disconnect the free connector 7509VC-A from the receptacle 7509VC.
(5) Do a resistance check of the sensor 21QJ at the tank wall connector 7509VC between pins L and Y AWM 284609.
Make sure the resistance is between 330 and 480 ohms.
If there is:

continuity as specified, go to Step (6)
no continuity as specified (resistance check out of range), go to Step (9).

NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.

(6) Replace the FLSCU-1 [7QJ] AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
(7) If the fault continues:
(a) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
(b) Disconnect the free connector 7509VC-A from the receptacle 7509VC.
(c) Do a check AWM 284609 of the aircraft wiring (sensor input wire - H) between the FLSCU-1 rack connector AB, pin 12A and the tank wall free connector 7509VC-A, pin L.
(d) Do a check AWM 284609 of the aircraft wiring (sensor input wire - L) between the FLSCU-1 rack connector AB, pin 12B and the tank wall free connector 7509VC-A, pin Y.
(e) Do a check AWM 284606 of the aircraft wiring (FLSCU-1 BITE 2 test command wire) between the FLSCU-1 rack connector AA, pin 15A and the FQIC rack connector AB, pin 14E.
(f) Do a check AWM 284609 of the aircraft wiring (FLSCU-1 LS6 output wire) between the FLSCU-1 rack connector AB, pin 2B and the FQIC rack connector AC, pin 3A.
(g) Repair all the unserviceable wiring and connectors ESPM 2053210.
(h) Connect the free connector 7509VC-A to the tank wall receptacle 7509VC.
(i) Do the test given in Para. 3.B.
(8) If the fault continues, do a test AWM 282603 with a MULTIMETER - STANDARD to see if 28VDC is available at the FLSCU-1 (7QJ) rack connector AA, pin 1D.
(a) If the 28VDC is available:

go to step (9).

(b) If the 28VDC is not available:
1 Do a check of the aircraft wiring AWM 282603 between:

the FLSCU-1 (7QJ) rack connector AA, pin 1D and the C/B-1QL.

2 Repair all the unserviceable wiring and connectors ESPM 2053210.
3 Do the test given in Para. 3.B.
(9) If the fault continues or if there is no continuity in Step (5):
(a) Drain, open and vent the tank AMM 28-10-00-910-001 AMM 28-10-00-910-002.
(b) Do a wiring check of the HARNESS-CHAN A, CTR TK [17QT] AWM 284609 and replace, if necessary AMM 28-42-44-000-001 and AMM 28-42-44-400-001.
(c) If the harness is serviceable, replace the SENSOR-LOW LVL, L CTR TK CHANNEL A [21QJ] AMM 28-46-15-000-004 and AMM 28-46-15-400-012.

Subtask 28-46-00-810-055-D ** ON A/C NOT FOR ALL

A. Procedure
(1) Do the steps applicable to the test equipment available.
(2) Test Equipment

(a) If there is:

approved test equipment available, go to Step (3)
no approved test equipment available, go to Step (6).

(3) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
(4) Disconnect the fused adaptor 7509VC-B from the receptacle 7509VC.
(5) Do a resistance check of the sensor 21QJ at the tank wall connector 7509VC between pins L and Y AWM 284609.
Make sure the resistance is between 330 and 480 ohms.
If there is:

continuity as specified, go to Step (6)
no continuity as specified (resistance check out of range), go to Step (9).

NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.

NOTE: The connections for the FLSS sensors are through connections and are not fused.

(f) Do a check AWM 284606 of the aircraft wiring (FLSCU-1 BITE 2 test command wire) between the FLSCU-1 rack connector AA, pin 15A and the FQIC rack connector AB, pin 7J.
(g) Do a check AWM 284609 of the aircraft wiring (FLSCU-1 LS6 output wire) between the FLSCU-1 rack connector AB, pin 2B and the FQIC rack connector AB, pin 3H.
(h) Repair all the unserviceable wiring and connectors ESPM 2053210.
(i) Install the fused adaptor between the tank wall receptacle 7509VC and the free connector 7509VC-A.
(j) Do the test given in Para. 3.B.
(8) If the fault continues, do a test AWM 282107 with a MULTIMETER - STANDARD to see if 28VDC is available at the FLSCU-1 (7QJ) rack connector AA, pin 1D.
(a) If the 28VDC is available:

go to step (9).

(b) If the 28VDC is not available:
1 Do a check of the aircraft wiring AWM 282107 between:

the FLSCU-1 (7QJ) rack connector AA, pin 1D and the C/B-31QA.

2 Repair all the unserviceable wiring and connectors ESPM 2053210.
3 Do the test given in Para. 3.B.
(9) If the fault continues or if there is no continuity in Step (5):
(a) Drain, open and vent the tank AMM 28-10-00-910-001 and AMM 28-10-00-910-002.
(b) Do a wiring check of the HARNESS-CHAN A, CTR TK [17QT] AWM 284609 and replace, if necessary AMM 28-42-44-000-001 and AMM 28-42-44-400-001.
(c) If the harness is serviceable, replace the SENSOR-LOW LVL, L CTR TK CHANNEL A [21QJ] AMM 28-46-15-000-004 and AMM 28-46-15-400-012.

[Rev.8 from Aug 2018] 2026.04.04 04:39:50 UTC