GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2003 🢒 CTS - RHD 🢒 Engine 🢒 Engine Controls - 2.6L and 3.2L 🢒 DTC P2123

Circuit Description

The accelerator pedal position (APP) sensor is made up of 2 sensors that are housed inside one assembly. The engine control module (ECM) supplies a separate 5-volt reference and low reference circuit for each of the sensors. The 5-volt reference for APP sensor 1 is supplied from the same source in the ECM as the 5-volt reference for the mass air flow (MAF) sensor and the fuel tank pressure (FTP) sensor. The 5-volt reference voltage for all of the sensors is supplied on separate ECM terminals, but the terminals are connected internally to a voltage supply. The APP sensor 1 sends a signal from the sensor to the ECM indicating the accelerator pedal position. The ECM actuates the throttle plates based on this information. The APP sensor 1 signal voltage increases as the pedal is depressed, from approximately 0.8 volts at rest to above 3.5 volts when fully depressed. If the ECM detects that the signal voltage is excessively high, DTC P2123 sets.

Conditions for Running the DTC
    • The ignition is ON.
    • The battery voltage is more than 10 volts.
    • The accelerator pedal is not in the rest position.

Conditions for Setting the DTC

The APP sensor 1 voltage is more than 4.8 volts for more than 140 milliseconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

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. Turn ON the ignition, with the engine OFF.
  2. Observe the accelerator pedal position (APP) sensor 1 voltage with a scan tool.

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

4.8 V

Go to Step 3

Go to Step 4

3
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the APP sensor 1 voltage with a scan tool.

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

0.02 V

Go to Step 6

Go to Step 13

4
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition.
  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 6

Go to Step 5

5
  1. Observe the DTC information with a scan tool.
  2. Slowly depress the accelerator pedal to wide open throttle (WOT), then slowly return the accelerator pedal to the closed position.
  3. Repeat this action several times.

Did the DTC fail this ignition?

--

Go to Step 19

Go to Intermittent Conditions

6
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the APP sensor 1 to a good ground with a DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 7

Go to Step 11

7
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the APP sensor 1 and the signal circuit of the APP sensor 2.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the APP sensor 1 voltage with the scan tool.

Is the APP sensor 1 voltage within the specified range?

4.8-5.2 V

Go to Step 8

Go to Step 13

8
  1. Turn OFF the ignition.

    2. Important: It may be necessary to remove the ECM/TCM fuse to allow the ECM to power down.

  2. Allow the engine control module (ECM) to completely power down. This can be verified by the loss of communication with the scan tool.
  3. Measure the resistance from the low reference circuit of the APP sensor 1 to a good ground with a DMM.

Is the resistance less than the specified value?

5 ohms

Go to Step 16

Go to Step 9

9

Test the low reference circuit of the APP sensor 1 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 21

Go to Step 10

10

Measure the resistance from the case of the ECM to the battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 17

Go to Step 15

11
  1. Measure the voltage from the 5-volt reference circuit of the APP sensor 1 to a good ground with a DMM.
  2. Observe the DMM as you disconnect all components that share the 5-volt reference voltage source one at a time.

Is the voltage within the specified range after disconnecting any component?

4.8-5.2 V

Go to Step 18

Go to Step 12

12

Test the 5-volt reference circuit of the APP sensor 1 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 21

Go to Step 14

13

Test the signal circuit of the APP sensor 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 21

Go to Step 17

14
  1. Test the 5-volt reference circuits of the following components for a short to voltage:
    2. • The mass air flow (MAF) sensor
    • The fuel tank pressure (FTP) sensor
  2. Repair as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

15

Repair the open or high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 21

--

16

Test for an intermittent and for a poor connection at the APP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

17

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

18

Replace the component that when disconnected, caused the voltage to return to the specified value. Refer to the appropriate replacement procedure.

Did you complete the replacement?

--

Go to Step 21

--

19

Replace the accelerator pedal assembly. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

21
  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 22

22

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