GM Service Manual Online
For 1990-2009 cars only
Table 1: APP Sensor Position Table
Table 2: DTC P1271 APP sensor 1-2 correlation

Circuit Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the engine control module (ECM). Each sensor has a unique functionality to determine pedal position as shown in the table below. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

APP Sensor Position Table

APP Sensor

Actual Pedal Position

% Depressed as Observed on a Scan Tool

Voltage as Observed on a Scan Tool

1

Pedal at rest

0

.52 - .80

1

Pedal at full travel

100

2.12 - 2.78

2

Pedal at rest

0

4.25 - 4.53

2

Pedal at full travel

100

2.24 - 2.93

3

Pedal at rest

0

3.95 - 4.13

3

Pedal at full travel

100

2.69 - 3.16

Conditions for Running the DTC

    • DTCs P1277, P1278, P1287, P1288, P1635, or P1639 are not set.
    • The ignition switch is in the crank or run position.
    • The ignition voltage is between 7-16 volts.

Conditions for Setting the DTC

    • The APP sensor 1 and APP sensor 2 are more than 10 percent out of range of each other.
    • All of the above conditions present for less than 1 second.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • If one or more APP sensor DTCs are set for a single APP sensor, the following occurs:
       - The control module will not command Reduced Engine Power mode.
       -  The control module will use the remaining two APP sensors to calculate throttle response.
    • If certain multiple APP sensor DTCs are set for more than one APP sensor, the following occurs:
       - The control module commands Reduced Engine Power mode.
       - The APP indicated angle is limited to a predetermined value to limit the amount of throttle control.
       - The message center displays Reduced Engine Power.
    • If all three APP sensors are out of range, the following occurs:
       - The control module commands Reduced Engine Power mode.
       - The APP indicated angle is limited to 0 percent. The control module only allows the engine to idle.
       - The message center displays Reduced Engine Power.

Conditions for Clearing the DTC

    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

DTC P1271 APP sensor 1-2 correlation

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Step 3

3

  1. Select the diagnostic trouble code (DTC) option using the scan tool.
  2. Lightly touch and move the related APP wiring harnesses and connectors while monitoring the DTC Information.

Did this DTC fail this ignition, during the above test ?

--

Go to Step 4

Go to Intermittent Conditions

4

Is DTC P1272 also set?

--

Go to Step 6

Go to Step 5

5

Is DTC P1273 also set?

--

Go to Step 12

--

6

  1. Turn OFF the ignition.
  2. Disconnect the APP sensor harness connector.
  3. Turn ON the ignition.
  4. With a test lamp connected to ground, test for voltage at the APP sensor 2, 5-volt reference circuit.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 16

7

Connect a test lamp between the APP sensor 2, 5-volt reference circuit and the APP sensor 2 low reference circuit

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 18

8

  1. Disconnect the test lamp.
  2. With the APP sensor harness connector still disconnected, observe the APP sensor 1 voltage parameter with a scan tool.

Is the APP sensor 1 voltage less than the specified value?

1 V

Go to Step 15

Go to Step 9

9

Is the APP sensor 2 voltage more than the specified value?

4 V

Go to Step 10

Go to Step 11

10

Test the APP sensor 1 signal circuit for a short to the APP sensor 3 signal circuit with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 12

11

Test the APP sensor 1 signal circuit for a short to the APP sensor 2 signal circuit with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 12

12

  1. Turn OFF the ignition.
  2. Disconnect the APP sensor harness connector.
  3. Turn ON the ignition.
  4. With a test lamp connected to ground, test for voltage at the APP sensor 1, 5-volt reference circuit.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 19

13

Connect the test lamp between the APP sensor 1, 5-volt reference circuit and the APP sensor 1 low reference circuit.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 20

14

  1. Connect a fused jumper wire between the APP sensor 1 signal circuit and the APP sensor 1, 5-volt reference circuit.
  2. With a scan tool, observe the APP sensor 1 voltage parameter.

Does the scan tool indicate voltage at the specified value?

5 V

Go to Step 21

Go to Step 15

15

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 1 signal circuit.
  3. With a DMM, test the APP sensor 1 signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

16

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 2, 5-volt reference circuit.
  3. With a DMM, test the APP sensor 2, 5-volt reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

17

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 2 signal circuit.
  3. Turn ON the ignition.
  4. With a DMM, test the APP sensor 2 signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

18

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 2 low reference circuit.
  3. With a DMM, test the APP sensor 2 low reference circuit for resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

19

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 1, 5-volt reference circuit.
  3. Turn ON the ignition.
  4. With a DMM, test the APP sensor 1, 5-volt reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

20

  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connector that contains the APP sensor 1 low reference circuit.
  3. With a DMM, test the APP sensor 1 low reference circuit for resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

21

Inspect for poor connections at the harness connector of the APP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 22

22

Replace the APP sensor assembly. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 25

--

23

Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 24

24

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25

  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 26

Go to Step 2

26

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK