Hummer H1 Service Manual page 1098

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DTC P0121 Accelerator Pedal Position (APP)
Sensor 1 Circuit Performance
Circuit Description
The Accelerator Pedal Position (APP) module provides a volt-
age signal that changes relative to accelerator pedal 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
• Ignition voltage greater than 6.4 volts.
• Engine speed greater than 300 RPM.
• The difference between APP 1 and APP 2 is greater than
.23 volts (PCM compares pre-scaled voltage (internal to
PCM)).
• The difference between APP 1 and APP 3 is greater than
.50 volts (PCM compares pre-scaled voltage (internal to
PCM)).
• No in range faults for APP 2 or APP 3 (PCM checks for
high and low voltage faults).
• 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 "Service Throttle Soon" lamp.
• Throttle will operate normally as long as there is only one
malfunction present. If there are two APP malfunctions
present, the PCM will turn "ON" the "Service Throttle
Soon" lamp and limit power. If a third APP malfunction is
present, the "Service Throttle Soon" lamp will be "ON"
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 B
RESUME YL
ACCEL
HOT IN RUN
AND START
SET GRN
COAST
FUSE 5C
10AMP
INTERIOR B
RD
ON/
OFF
295 BR
PCM/Tech 1 Scan Tool 33
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
154 TN C28-D14
SOLENOID
CONTROL
C 37
C27-D10 RESUME
153 LG
ACCEL
SIGNAL
D
42
SET
C29-B11
152 DB
COAST
SIGNAL
A 29
151 GY C29-A11
ON / OFF
SIGNAL
C1
9-S12-055
and only allow the engine to operate at 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
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
was closed to over about 3.7 volts when throttle is held at Wide
Open Throttle (WOT) position. The following chart will check
voltages on all APP circuits to see if they fall in normal ranges.
The PCM compares pre-scaled voltages (these are voltages that
the scan tool can't read). The scan tool reads only output volt-
ages.
Test Description
Number(s) below refer to the number(s) on the diagnostic table.
1. This step determines if there is a good 5 volt reference.
2. This step will check for an open in the ground circuit.
3-1-01