Hummer H1 Service Manual page 1180

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DTC P1643 Wait to Start Lamp Control Circuit
FUSE 4B
5 AMP
INTERIOR
FUSE BOX
TO
IGNITION
SWITCH
Circuit Description
A dash light (Wait To Start) is illuminated by the PCM when
the glow plugs are commanded ON. When the PCM is com-
manding the Wait To Start lamp ON, the voltage potential of
the circuit will be low (near 0 volts). When the PCM is com-
manding the Wait To Start lamp OFF, the voltage potential of
the circuit will be high (near battery volts). The primary func-
tion of the PCM is to supply the ground for the Wait To Start
lamp circuit. This is a type B DTC.
Conditions for Setting the DTC
• Wait To Start lamp requested ON.
• Voltage on Wait To Start tamp circuit high (near battery
volts).
or
• Wait To Start lamp requested OFF.
• Voltage on Wait To Start lamp control circuit low (near
0 volts).Action Taken When the DTC Sets
Action Taken When the DTC Sets
No Wait To Start lamp.
05745159
PCM/Tech 1 Scan Tool 115
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
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.
Diagnostic Aids
A faulty bulb or the control circuit shorted to ground will cause
a P1643 to set.
Test Description
5. Repeat the command as many times as necessary (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 OFF for 12 seconds. After the
12 seconds has elapsed, the glow plugs can be commanded
ON again).
9. If no trouble is found in the control circuit or the connection
at the PCM, the PCM maybe malfunctioning, however, this
is an extremely unlikely failure.
HOT IN RUN
AND START
TO
STARTER
POS. STUD
FUSIBLE
LINK
BATT +
GLOW PLUG
RELAY
00-S12-011