Hummer H1 Service Manual page 1142

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DTC P0263, P0266, P0269, P0272, P0275,
P0278, P0281 and P0284 Cylinder Balance
System Faults
WATER IN
FUEL LIGHT
DRAIN
LEFT HAND
FILTER
STATUS CENTER
C9-D
C3-F4
C1-45
B
9-S12-056
Circuit Description
The PCM has the ability to increase and decrease the amount
of fuel to each cylinder to provide smooth idle operation. If the
fuel correction exceeds define limits, DTC P0263 will set. This
is a type D DTC.
Conditions for Setting the DTC
• Engine at idle.
• Engine coolant at normal temperatures.
• Cylinder fault must be constant.
• Fuel correction amount exceeds limits (internal to
PCM).
• Conditions met for 2 seconds.
Action Taken When the DTC Sets
Possible rough idle.
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
05745159
30 GY
HOT IN RUN
AND START
C9-J
C3-N7
FUSE 4B FUSE 3B
5AMP 20AMP
INTERIOR EXTERIOR
FUSE BOX FUSE BOX
TO
IGNITION
SWITCH
291 PK
A
C
WATER IN
FUEL
SENSOR
C
A
POWER
CONTROL
MODULE
G2
HOT IN RUN
AND START
FUSE 3A
20AMP
EXTERIOR
FUSE BOX
C5-A4
239 PK
A
ENGINE
SHUTOFF
SOLENOID
A
FUEL
FUEL
SOLENOID
HEATER
DRIVER
C28-C15 C28-D3
ESO
FUEL INJECT
SOLENOID
CONTROL
CONTROL
temperature and engine coolant temperature exceeds
71°C (160°F) that same ignition cycle).
• Use of a Scan Tool.
Diagnostic Aids
Injector balance test on scan tool should be used to confirm
faulty cylinder. Scan tool will cutout specific cylinder re-
quested. If original complaint was multiple cylinder balance
DTCs and vehicle has a manual transmission, dual mass fly-
wheel could be at fault. It's possible that if a cylinder balance
fault has been detected and engine has been running for a long
time, the PCM will try to increase or decrease fuel in other cyl-
inders to compensate for a rough idle which will cause multiple
cylinder balance DTCs to set. The scan tool snap shot mode
can be used to properly identify the suspected cylinder. The
most likely cause of cylinder balance DTCs are faulty nozzles
or engine mechanical (low compression) problems.
Test Description
Number(s) below refer to the number(s) on the diagnostic ta-
ble.
2. This step will properly identify a suspected cylinder by
looking for a RPM drop (if RPM drops, cylinder is contrib-
uting, if not, cylinder is not contributing).
PCM/Tech 1 Scan Tool 77
A
FUEL
SOLENOID
B
D B F
IGN FUEL FUEL
SOLENOID SOLENOID
HIGH LOW
FUEL
CLOSURE CLOSURE
SOLENOID
SIGNAL GROUND
CONTROL
A
E C
C28-C3 C27-C13 C29-A1
CLOSURE CLOSURE
SIGNAL GROUND