Hummer H1 (2002+). Manual - part 275

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PCM/Tech 1 Scan Tool 33

05745159

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”

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.

FUSE 5C
10AMP
INTERIOR

FUSE 3A
10 AMP
EXTERIOR

ON/
OFF

SET
COAST

RESUME
ACCEL

HOT IN RUN
AND START

C29-A11

C29-B11

C27-D10

C28-D14

C28-C2

C27-D12

C27-D3

C27-D4

C27-D6

C29-B2

C29-B1

C27-C5

C29-A12

C5-D3

C5-A4

154 TN

151 GY

152 DB

153 LG

ON / OFF
SIGNAL

SET
COAST
SIGNAL

RESUME
ACCEL
SIGNAL

WASTEGATE
SOLENOID
CONTROL

5 VOLT
REFERENCE

APP 3
SIGNAL

GROUND

APP 1
SIGNAL

GROUND

720 TN

717 WH

723 YL

724 DG

725 GY

718 DB

719 BR

721 LB

722 PP

ACCELERATIOR
PEDAL POSITION
SENSOR

POWERTRAIN
CONTROL
MODULE
(PCM)

APP 2
SIGNAL

9-S12-055

295 BR

GRN

3-1-01

PCM/Tech 1 Scan Tool

_____________________________________________________

DTC P0121 - Accelerator Pedal Position (APP) Sensor 1 Circuit Performance

Step

Action

Value(s)

Yes

Important:

Before clearing DTC(s) use the scan tool “Capture Info” to

record Freeze Frame and Failure Record for reference, as data will be lost
when “Clear Info” function is used.

Was the “On-Board Diagnostic (OBD) System Check” performed?

—

Go to Step 2. Go to OBD Sys-

tem Check.

1. Ignition “ON”, engine “OFF”.
2. With the throttle closed, observe APP voltages on the scan tool.

Are APP voltages at specified values?

.45-.95v
4.0-4.5v
3.6-4.0v

Go to Step 3. Go to Step 4.

DTC is intermittent. If no additional DTCs are stored, refer to “Diagnostic
Aids”. If additional DTCs were stored, refer to those chart(s).

—

Go to the

applicable

DTC table.

Go to

Diagnostic

Aids.

1. Disconnect the APP sensor electrical connector.
2. Ignition “ON”, engine “OFF”.

3. With J–39200 connected to ground, probe APP sensor 5 volt reference

circuits at APP harness terminals “G”, “D” and “E”.

Is voltage at the specified value on all circuits?

4.75v

Go to Step 5. Go to Step 6.

1. Ignition “ON”, engine “OFF”.
2. With a test light connected to B+, probe APP sensor ground circuits at

the APP sensor harness terminals “A”, “B” and “J”.

Is Test light ON (all circuits)?

—

Go to Step 9.

Go to Step 8.

1. Ignition “OFF”.
2. Disconnect the PCM and check the 5 volt reference circuit for an open or

short to ground.

3. If the 5 volt reference circuit is open or shorted to ground, repair as nec-

essary.

Was the 5 volt reference circuit open or shorted to ground?

—

Go to Step 11.

Go to Step 8.

Check the 5 volt reference circuit for a poor connection at the PCM and
replace terminal if necessary.
Did the terminal require replacement?

—

Go to Step 11. Go to Step 10.

1. Ignition “OFF”.
2. Disconnect the PCM, and check for an open sensor ground circuit to the

PCM.

3. If problem is found, repair as necessary.

Was APP sensor ground circuit open?

—

Go to Step 11. Go to Step 10.

Replace the APP module.

Is Action complete?

—

Go to Step 11.

—

Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must
be programmed. Go to PCM replacement and programming procedures.
Is the action complete?

—

Go to Step 11.

—

1. Using the Scan Tool, select “DTC”, “Clear Info”.
2. Start engine and idle at normal operating temperature.

3. Select “DTC”, “Specific”, then enter the DTC number which was set.

4. Operate vehicle within the conditions for setting this DTC as specified in

the supporting text.

Does the Scan Tool indicate that this diagnostic Ran and Passed?

—

Go to Step 12.

Go to Step 2.

Using the Scan Tool, select “Capture Info”, “Review Info”.
Are any DTCs displayed that have not been diagnosed?

—

Go to the

applicable

DTC table

System OK

_____________________________________________________

PCM/Tech 1 Scan Tool 35

05745159

DTC P0122 Accelerator Pedal Position (APP)
Sensor 1 Circuit Low 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 less than .25 volts on APP 1.

• 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 malfunctioning. If two different APP
sensors have a malfunction, the “Check Throttle” lamp
will light and the PCM will limit power. If three APP
sensors have a malfunction present, the “Service Throt-
tle Soon” lamp will light and the PCM will only allow
the engine to operate at idle.

Conditions for Clearing the MIL/DTC

• A History DTC will clear when forty consecutive

• 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 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 DTC P0122 will result if the signal
or reference circuit are open.

Test Description

Number(s) below refer to the number(s) on the diagnostic ta-
ble.

2. This step determines if P0122 is the result of a hard failure or

an intermittent condition.

4. This step checks the PCM and wiring.

FUSE 5C
10AMP
INTERIOR

FUSE 3A
10 AMP
EXTERIOR

ON/
OFF

SET
COAST

RESUME
ACCEL

HOT IN RUN
AND START

C29-A11

C29-B11

C27-D10

C28-D14

C28-C2

C27-D12

C27-D3

C27-D4

C27-D6

C29-B2

C29-B1

C27-C5

C29-A12

C5-D3

C5-A4

154 TN

151 GY

152 DB

153 LG

ON / OFF
SIGNAL

SET
COAST
SIGNAL

RESUME
ACCEL
SIGNAL

WASTEGATE
SOLENOID
CONTROL

5 VOLT
REFERENCE

APP 3
SIGNAL

GROUND

APP 1
SIGNAL

GROUND

720 TN

717 WH

723 YL

724 DG

725 GY

718 DB

719 BR

721 LB

722 PP

ACCELERATIOR
PEDAL POSITION
SENSOR

POWERTRAIN
CONTROL
MODULE
(PCM)

APP 2
SIGNAL

9-S12-055

295 BR

GRN

PCM/Tech 1 Scan Tool

_____________________________________________________

DTC P0122 - Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage

Step

Action

Value(s)

Yes

Important:

Before clearing DTC(s) use the scan tool “Capture Info” to record Freeze

Frame and Failure Record for reference, as data will be lost when “Clear Info” func-
tion is used.

Was the “On-Board Diagnostic (OBD) System Check” performed?

—

Go to

Step 2.

Go to OBD

System
Check.

1. Ignition “ON”, engine “OFF”.
2. With the throttle closed, observe APP 1 voltages on the scan tool.

Is APP 1 voltages less than or equal to specified value?

.25v

Go to

Step 3.

Go to

Step 4.

DTC is intermittent. If no additional DTCs are stored, refer to “Diagnostic Aids”. If
additional DTCs were stored, refer to those table(s) first.

Are additional DTCs stored?

—

Go to the

applicable

DTC table.

Go to

Diagnostic

Aids.

1. Disconnect the APP sensor electrical connector.
2. Jumper APP 1 5 volt reference circuit and the APP 1 signal together at the APP

sensor harness connector.

3. Observe the APP 1 voltage on the Scan Tool.

Is APP 1 voltage greater than the specified value?

4.75v

Go to

Step 10.

Go to

Step 5.

1. Connect a test light between B+ and the APP 1 sensor signal circuit at the APP

sensor harness connector.

2. Observe the APP 1 voltage on the Scan Tool.

Is APP 1 voltage greater than the specified value?

4.75v

Go to

Step 6.

Go to

Step 8.

1. Ignition “OFF”.
2. Disconnect the PCM and check the 5 volt reference circuit for an open or short to

ground.

3. If the 5 volt reference circuit is open or shorted to ground, repair as necessary.
Was the 5 volt reference circuit open or shorted to ground?

—

Go to

Step 12.

Go to

Step 7.

Check the 5 volt reference circuit for a poor connection at the PCM and replace termi-
nal if necessary. Did the terminal require replacement?

—

Go to

Step 13.

Go to

Step 12.

1. Ignition “OFF”.
2. Disconnect the PCM, and check the APP 1 signal circuit for an open, short to

ground.

3. If the APP 1 sensor signal circuit is open or shorted to ground, repair as necessary.

Was APP 1 signal circuit open or shorted to ground?

—

Go to

Step 13.

Go to

Step 9.

Check the APP 1 sensor signal circuit for a poor connection at the PCM and replace
terminal if necessary. Did the terminal require replacement?

—

Go to

Step 13.

Go to

Step 12.

Check for a poor electrical connection at the APP module and repair if necessary.
Was a problem found?

—

Go to

Step 13

Go to

Step 11

Replace the APP module.

Is Action complete?

—

Go to

Step 13.

—

Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must be pro-
grammed. Go to PCM replacement and programming procedures.
Is the action complete?

—

Go to

Step 13.

—

1. Using the Scan Tool, select “DTC”, “Clear Info”.
2. Start engine and idle at normal operating temperature.

3. Select “DTC”, “Specific”, then enter the DTC number which was set.

4. Operate vehicle within the conditions for setting this DTC as specified in the sup-

porting text.

Does the Scan Tool indicate that this diagnostic Ran and Passed?

—

Go to

Step 14.

Go to

Step 2.

Using the Scan Tool, select “Capture Info”, “Review Info”.
Are any DTCs displayed that have not been diagnosed?

—

Go to the

applicable

DTC table

System OK

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