GM Service Manual Online
For 1990-2009 cars only
Table 1: APP Sensor Position Table
Table 2: DTC P2123

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 the 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 the 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 P0641 or P0651 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 voltage is more than 4.75 volts.
    • The above condition is 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 P2123

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 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. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Step 3

3

  1. Select the diagnostic trouble code (DTC) option on the scan tool.
  2. Lightly touch and move the related accelerator pedal position (APP) sensor wiring harnesses and connectors while monitoring the DTC information.

Did this DTC fail this ignition during the above test?

--

Go to Step 9

Go to Intermittent Conditions

4

  1. Disconnect the APP sensor harness connector.
  2. Observe the APP sensor 1 voltage parameter with a scan tool.

Does the scan tool indicate the APP sensor 1 voltage at the specified value?

0 V

Go to Step 5

Go to Step 6

5

  1. Connect a fused jumper between the APP sensor 2 signal circuit and the APP sensor 1 low reference circuit.
  2. Observe the APP sensor 2 voltage parameter with a scan tool.

Does the scan tool indicate APP sensor 2 voltage at the specified value?

0 V

Go to Step 10

Go to Step 8

6

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) harness connector containing the APP sensor 1 signal circuit.
  3. Turn ON the ignition.
  4. Test the APP sensor 1 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Disconnect the other ECM harness connector.
  3. Test the APP sensor 1 signal circuit for a short to all other APP circuits at the APP sensor harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

8

  1. Disconnect the ECM harness connector containing the APP sensor 1 low reference circuit.
  2. Test the APP sensor 1 low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

9

Repair the intermittent condition as necessary. Refer to Connector Repairs and Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 14

--

10

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 14

Go to Step 12

11

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 14

Go to Step 13

12

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

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK