TM-9-2320-272-23-2

TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)

TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 2 OF 5

SEPTEMBER 2012

TM-9-2320-272-23-2 - Page 271 of 1417

G04: CHARGING CIRCUIT AND BATTERY VOLTAGE TEST - Continued

STEP

2.

Generator operation.

a.

Check generator indicator for normal reading.

b.

Turn headlights and accessories off (TM 9-2320-272-10).

c.

Shut off engine (TM 9-2320-272-10).

CONDITION/INDICATION

Does generator indicator gauge read normal?

DECISION

YES - Perform G05: Engine Warmup/Coolant Check/Oil Pressure Test (WP

0192).

NO - Perform Battery/Alternator Gauge Inoperative troubleshooting (Volume 1, WP

0108).

STEP

3.

Battery voltage.

Check battery voltage.

CONDITION/INDICATION

Is battery voltage low?

DECISION

YES - Go to Step (4).

NO - If voltage is high, replace alternator M939/A1 60 amp (WP

0300),

M939A2 60 amp (WP

0301), 100 amp (Volume 5, WP

0780). After repairs are complete rerun GO-chain test

to verify problem is fixed.

STEP

4.

Battery voltage test.

a.

Battery voltage low.

b.

Allow vehicle to run 5 minutes and watch display.

c.

If voltage is not within limits, turn headlights and accessories off (TM 9-2320-272-10).

d.

If voltage is not within limits, shut off engine (TM 9-2320-272-10).

CONDITION/INDICATION

Is battery voltage within limits?

DECISION

YES - Go to Step (5).

NO - Perform NG50: Charging Circuit Test (WP

0201).

TM 9-2320-272-23-2

0191

0191-2