Hummer H1 Service Manual page 1147

82 PCM/Tech 1 Scan Tool
DTC P0370 Timing Reference High
Resolution
C27-D14
Circuit Description
The optical sensor provides a high resolution signal to the
PCM by counting pulses on the sensor disk located in the injec-
tion pump. The high resolution is one of the most important in-
puts by the PCM for fuel control and timing. This test monitors
the number of high resolution pulses which have been missed
(not detected). It's based on a comparison between the number
of pulses that were detected since the last pump cam pulse and
the number of the pulses that should have occurred. This is a
type A DTC.
Conditions for Setting the DTC
A number of High Resolution pulses (internal to PCM) per ev-
ery 8 cam reference pulses.
Action Taken When the DTC Sets
Backup fuel.
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
_____________________________________________________
A
5 VOLT
REFERENCE
PUMP CAM HIGH
SENSOR RESOLUTION SENSOR
GROUND
SIGNAL SIGNAL
B C D
C3 B8 C1
C5
C29-A4 C29-A2
5 VOLT CAM HIGH
REFERENCE SENSOR RES
SIGNAL SIGNAL
E
OPTICAL/ FUEL
TEMP SENSOR
F D
C12 C2
C27-D9 C27-C8 A7
C29
SENSOR FUEL TEMP ITS
GROUND SIGNAL HI
temperature and engine coolant temperature exceeds
71°C (160°F) that same ignition cycle).
• Use of a Scan Tool.
Diagnostic Aids
When PCM is in backup fuel, fast idle and poor performance
problems will exist. If P0251 is also stored, the snap shot mode
on the scan tool should be used to properly identify fault. It is
possible P0370 may set if there is air in fuel system (vehicle
running out of fuel).
Test Description
Number(s) below refer to the number(s) on the diagnostic ta-
ble.
2. This step will determine if there is a 5 volt reference.
3. This step checks the ground circuit.
4. This step will check to see if the sensor is sending a signal
back to the PCM.
INJECTION TIMING
STEPPEN MOTOR (ITS)
M
A B C
A3 A2 A6 A7
A8 A9 A10
ITS ITS ITS
LO LO HI
POWERTRAIN
CONTROL
MODULE
9-S12-070
®