Loss of the 28VDC Power Supply of the ECU on the Engine 1

TASK 73-25-00-810-946-A
Loss of the 28VDC Power Supply of the ECU on the Engine 1

1. Possible Causes

EIU-1 [1KS1]
ECU [4000KS]
aircraft wiring
C/B-ENGINE/ENG1/FADEC B/AND EIU 1 [4KS1]
harness J2

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 73-21-60-000-001	Removal of the Electronic Control Unit (ECU)
AMM 73-21-60-400-001	Installation of the Electronic Control Unit (ECU)
ASM 732505
ASM 732508
AMM 73-25-34-000-040	Removal of the Engine Interface Unit (EIU)
AMM 73-25-34-400-040	Installation of the Engine Interface Unit (EIU)
AMM 73-29-00-710-040	Operational Test of the FADEC on the ground (with Engine Motoring)

3. Fault Confirmation
Subtask 73-25-00-865-054-A ** ON A/C NOT FOR ALL

A. Make sure that this(these) circuit breaker(s) is(are) closed:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	ENGINE/ENG1/FADEC B/AND EIU 1	4KS1	R41

Subtask 73-25-00-710-339-A ** ON A/C NOT FOR ALL

B. Test
(1) If the circuit breaker (4KS1) is open, refer to Para. 4.A.(2).
(2) Do the operational test of the FADEC 1B on the ground (with engine motoring) AMM 73-29-00-710-040.

4. Fault Isolation
Subtask 73-25-00-810-198-A ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message EIU - 28V, ECU:

do a check of the status of the circuit breaker (4KS1).

(1) If the circuit breaker is closed:

disconnect the connector J2 from the ECU (4000KS) and do a check for 28VDC at pin J2/13 with the FADEC GND PWR pushbutton switch released (the ON legend is on) ASM 732505.

(a) If there is 28VDC:

replace the EIU-1 [1KS1] (the most possible failure is the EIU 28V relay) AMM 73-25-34-000-040 and AMM 73-25-34-400-040
replace the ECU [4000KS] (the most possible failure is an ECU diode) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If there is no 28VDC:

do a check for 28VDC at EIU 1 (1KS1) pin AC/9 ASM 732505.

1 If there is no 28VDC:

do a check for open or short to ground at the aircraft wiring from the circuit breaker (4KS1) to EIU 1 (1KS1) pins AC/9.

a If there is a short to ground:

repair the above wiring.

b If there is no short to ground:

replace the C/B-ENGINE/ENG1/FADEC B/AND EIU 1 [4KS1] .

2 If there is 28VDC:

do a check for open or short to ground at the harness J2 between the EIU 1 (1KS1) and the ECU (4000KS), pin AC/2 to pin J2/13. Replace the harness J2 if necessary ASM 732505.

3 If the fault continues:

make sure that there is no ground signal at EIU 1 (1KS1) pin AA/5B ASM 732508.

replace the EIU-1 [1KS1] AMM 73-25-34-000-040 and AMM 73-25-34-400-040.

(2) If the circuit breaker (4KS1) is open:

close the circuit breaker.

(a) If the circuit breaker trips:

replace the EIU-1 [1KS1] AMM 73-25-34-000-040 and AMM 73-25-34-400-040
replace the ECU [4000KS] AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(b) If the fault continues:

do a check for a short to ground at the harness J2 between the EIU 1 (1KS1) and the ECU (4000KS), pin AC/2 to pin J2/13.

1 If there is a short to ground:

replace the harness J2 .

2 If there is no short to ground:

do a check for a short to ground at the aircraft wiring between EIU 1 (1KS1) pin AC/9 and the circuit breaker (4KS1).

a If there is a short to ground:

repair the above wiring.

b If there is no short to ground:

replace the C/B-ENGINE/ENG1/FADEC B/AND EIU 1 [4KS1] .

Subtask 73-25-00-710-340-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.B.

[Rev.8 from Aug 2018] 2026.04.04 04:35:51 UTC