Hummer H1 Service Manual page 1102

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DTC P0123 Accelerator Pedal Position (APP)
Sensor 1 Circuit High Voltage
Circuit Description
The Accelerator Pedal Position (APP) module provides a volt-
age signal that changes relative to accelerator position. There
are three sensors located within the APP module that are scaled
differently. This is a type C DTC.
Conditions for Setting the DTC
• Voltage is greater than 4.75 volts on APP 1 sensor.
• Conditions met for 2 seconds.
Action Taken When the DTC Sets
• The input from APP 1 sensor is ignored.
• A current and history DTC will set but it will not turn on
the "Check Throttle" lamp. The throttle will operate
normally as long as there is only one sensor malfunc-
tioning. If two different APP sensors have a malfunc-
tion, the "Check Throttle" lamp will light and the PCM
will limit power. If three APP sensors have a malfunc-
tion present, the "Service Throttle Soon" lamp will light
and the PCM will only allow the engine to operate at
idle.
05745159
ACCELERATIOR
PEDAL POSITION
SENSOR
44
D B
32
C
2
53
G A
17
F
1
60
E J
15
K
3
14
20
HOT IN RUN
22
AND START
C1
FUSE 3A
10 AMP
EXTERIOR
C5-A4
A
RESUME
ACCEL
HOT IN RUN
AND START
SET
COAST
FUSE 5C
10AMP
INTERIOR B
ON/
295 BR OFF
PCM/Tech 1 Scan Tool 37
POWERTRAIN
CONTROL
MODULE
(PCM)
722 PP C29-A12
GROUND
721 LB C27-C5 APP 2
SIGNAL
719 BR C29-B1
GROUND
718 DB C29-B2 APP 1
SIGNAL
725 GY C27-D6
GROUND
724 DG C27-D4 APP 3
SIGNAL
723 YL C27-D3
717 WH C27-D12
5 VOLT
REFERENCE
720 TN C28-C2
C5-D3
WASTEGATE
B
154 TN C28-D14
SOLENOID
CONTROL
C
37 C27-D10 RESUME
YL 153 LG
ACCEL
SIGNAL
D
42
SET
C29-B11
GRN 152 DB
COAST
SIGNAL
A 29
RD 151 GY C29-A11 ON / OFF
SIGNAL
C1
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 Tool
Diagnostic Aids
A scan tool reads APP 1 position in volts. It should read about
.45 to .95 volt with throttle closed and ignition "ON" or at idle.
Voltage should increase at a steady rate as throttle is moved to-
ward Wide Open Throttle (WOT). Also, 90% pedal travel is
acceptable for correct APP operation. Scan APP 1 sensor while
depressing accelerator pedal with engine stopped and ignition
"ON". Display should vary from about .74 volt when throttle is
closed to about 3.7 volts when throttle is held at Wide Open
Throttle (WOT) position. A P0123 will result if the ground cir-
cuit is open or the signal circuit is shorted to voltage. Refer to
Intermittents in Section 2.
Test Description
Number(s) below refer to the number(s) on the diagnostic ta-
ble.
2. This step determines if DTC P0123 is the result of a hard
failure or an intermittent condition.
3. This step checks the PCM and wiring.
9-S12-055