Hummer H1 Service Manual page 1178

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DTC P1641 Malfunction Indicator Lamp
(MIL) Control Circuit
C28-C13
C28-D6
Circuit Description
A dash light is illuminated by the PCM if diagnostics have de-
tected certain errors related to the engine performance or en-
gine sensor status. Illumination is accomplished by the PCM
providing a ground path for the lamp circuit. This is a type D
DTC.
Conditions for Setting the DTC
• MIL requested "ON".
• Voltage at the MIL control circuit is greater than 0 volts.
or
• MIL requested "OFF".
• Voltage at the MIL control circuit is greater than 0 volts.
Action Taken When the DTC Sets
Will not turn "ON" the MIL.
05745159
HOT AT HOT IN RUN
ALL TIMES AND START
FUSE 2D FUSE 3A
20 AMP 20 AMP
INTERIOR EXTERIOR
C1-10
TO
C29-B3
C28-D13 C28-C12
BATT BATT IGN
GROUND GROUND
C28-D7
HOT AT
ALL TIMES
G2
PCM/Tech 1 Scan Tool 113
HOT IN RUN
AND START
STS
LAMP LAMP
C10-H
C3-G5
C1-25
C28-C11 C28-D11 C28-C14
IGN STS LAMP
CONTROL CONTROL
59 BK
FUSE 1H
5 AMP
INTERIOR
G4
554 GRY
Conditions for Clearing the MIL/DTC
• 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.
Diagnostic Aids
A faulty bulb or the control circuit shorted to ground will cause
a P1641 to set.
Test Description
Number(s) below refer to the number(s) on the diagnostic ta-
ble.
3. This test will check the control circuit for a short to ground.
5. This test will check the control circuit for an open.
FUSE 4B
5 AMP
INTERIOR
C10-J
STATUS
MIL
CENTER
C10-C
C3-F3
C1-28
MIL
POWERTRAIN
CONTROL
MODULE
SERIAL DATA
CLASS II
C28-C8
DLC
4 2
16
9-S12-064