TM 1–1520–238–T–3
18–3
18–5 SIGNAL NAME:
APU FUEL SHUTOFF
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
12
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU fuel shutoff valve.
REMARKS: From fuel shutoff solenoid through APU speed electronic control unit and DASEC to
FCC.
PASS:
If third digit on HOD is 2, 3, 6, or 7, go to paragraph 18–6.
FAIL: Location of fault: fuel shutoff solenoid, wiring from fuel shutoff solenoid to APU speed electronic
control unit, wiring from APU speed electronic control unit to DASEC. Troubleshoot wiring to
isolate fault (TM 1–1520–238–T–8).
18–6 SIGNAL NAME:
APU START RELAY ENERGIZED
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
11
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU start relay.
REMARKS: From APU speed electronic control unit to APU start solenoid and through DASEC to
FCC.
PASS:
If third digit on the HOD is 4, 5, 6, or 7, go to paragraph 18–7.
FAIL: Location of fault: APU speed electronic unit, wiring from APU speed electronic unit to APU start
solenoid, wiring from APU speed electronic unit to DASEC to FCC (TM 1–1520–238–T–8).
18–7 SIGNAL NAME:
APU OVERCURRENT IND
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
10
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU fuel shutoff solenoid current, power takeoff (PTO) clutch
solenoid, APU start solenoid, and ignition.
REMARKS: From APU speed electronic control unit through DASEC to FCC.
PASS:
If fourth digit on the HOD is 1, 3, 5, or 7, go to paragraph 18–8.
FAIL: Location of fault: APU speed electronic control unit, wiring from APU speed electronic control
unit to DASEC. Troubleshoot wiring to isolate fault (TM 1–1520–238–T–8).
18–8 SIGNAL NAME:
APU PTO CLUTCH ENGAGED
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
9
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU PTO clutch engagement.
REMARKS: From APU PTO clutch solenoid through APU speed electronic control unit and DASEC to
FCC.
PASS:
If fourth digit on the HOD is 2, 3, 6, or 7, go to paragraph 18–9.
FAIL: Location of fault: APU PTO clutch solenoid, wiring from APU PTO clutch solenoid to APU
speed electronic control unit, wiring from APU speed electronic control unit to DASEC.
Troubleshoot wiring to isolate fault (TM 1–1520–238–T–8).
