Low Voltage - Hummer H1 Service Manual

66 PCM/Tech 1 Scan Tool
DTC P0231 Fuel Lift Pump Secondary Circuit

Low Voltage

SELECTOR SWITCH
Circuit Description
The status of the lift pump is monitored by the PCM. This sig-
nal is also used to store a DTC if the fuel pump relay is defec-
tive or fuel pump voltage is lost while the engine is running.
There should be about 12 volts on circuit 120 during glow plug
cycle. This is a Type B DTC.
Conditions for Setting the DTC
• Fuel lift pump commanded "ON".
• Ignition voltage minus 4 volts.
• Fuel lift pump voltage less than ignition voltage value.
• Conditions met for 2 seconds.
Action Taken When the DTC Sets
No action taken.
_____________________________________________________
TO FUEL
787 GY
B
FUEL
LIFT
PUMP
M
A
G2
FUSE 2D
20A
INTERIOR
C1-10
537 OR
FUEL PUMP
RELAY
EXTERIOR
FUSE BOX
787 GY
G2
C27-D5
FUEL LIFT
PUMP SIGNAL RELAY CONTROL
9-S12-051
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
This DTC will not check the fuel pump operation.
Test Description
Number(s) below refer to the number(s) on the diagnostic ta-
ble.
3. This step will check the fuel pump circuit.
C27-D8
FUEL PUMP
POWERTRAIN
CONTROL
MODULE
9-S12-051
®