Hummer H1 Service Manual page 1150

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DTC P0380 Glow Plug Circuit Performance
FUSE 4B
5 AMP
INTERIOR
FUSE BOX
TO
IGNITION
SWITCH
Circuit Description
The glow plug system is used to assist in providing the heat re-
quired to begin combustion during engine starting at cold am-
bient temperatures. The glow plugs are heated before and
during cranking, as well as initial engine operation. The PCM
controls the glow plug "ON" times by monitoring coolant tem-
peratures and glow plug voltage. The PCM also monitors glow
plugs individually to detect a failure. Once a failure has been
detected, a diagnostic signal is sent to the PCM so the diagnos-
tic code and MIL can be activated. This is a type B code.
Action Taken When the DTC Sets
Hard start or no start and possible white smoke.
Conditions for Clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive
trips without a fault condition.
• A History DTC will clear when forty consecutive
warm-up cycles that the diagnostic does not fail (coolant
temperature has risen 5°C (40°F) from start up coolant
temperature and engine coolant temperature exceeds
71°C (160°F) that same ignition cycle).
• Use of a Scan Tool.
05745159
PCM/Tech 1 Scan Tool 85
FUSE 3A
20 AMP
EXTERIOR
C5-A4
A B C D D
LEFT IGN
BANK POWER
OUTPUT
A
B
RIGHT
BANK
C
OUTPUT
D
C A B
Diagnostic Aids
IF a P0380 DTC sets after the PCM has been flashed, the glow
plug system must be relearned. Refer to (LINK-GOTO-RE-
PAIR-609502) Glow Plug System Type Relearn. If glow plug
relay is stuck in the "ON" position, check for proper operation
of glow plugs. When glow plugs are commanded "ON" by the
Scan Tool, an internal PCM timer protects the glow plugs from
damage by cycling them "ON" for 3 seconds and then "OFF"
for 12 seconds. The glow plug relay battery feed wire nut
should be tested for proper torque. The California glow plug
system will send the following volages.
HOT IN RUN
AND START
TO
STARTER
POS. STUD
FUSIBLE
LINK
BATT +
GLOW PLUG
RELAY
00-S12-011