GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The accelerator pedal position (APP) sensor 1 and the APP sensor 2 are potentiometer type sensors, each with the following circuits:

    • A 5-volt reference circuit
    • A low reference circuit
    • A signal circuit

The control module provides the APP sensors with a 5-volt reference circuit and a low reference circuit. The APP sensors then provide the control module signal voltages proportional to pedal movement. The APP sensor 1 signal voltage is low at rest and increases as the pedal is depressed. The APP sensor 2 signal voltage is low at rest and increases as the pedal is depressed. When the control module detects that the APP sensor 1 and the APP sensor 2 signal circuits are out of correlation with each other, DTC P1125 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1125 Accelerator Pedal Position (APP) System

Conditions for Running the DTC

    • DTC P2108 or U0107 is not set.
    • The ignition is in the Crank or Run position.
    • The ignition voltage is more than 5.23 volts.
    • DTC P1125 runs continuously once the above conditions are met.

Conditions for Setting the DTC

    • Both APP sensors are out of range.
        OR
    • Both APP sensors disagree.
        OR
    • One APP sensor is out of range and the other APP sensor disagrees.
    • One of the above conditions is present for more than 0.019 second.

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 and/or the Failure Records.
    • The control module commands the TAC system to operate in the Reduced Engine Power mode.
    • A message center or an indicator displays Reduced Engine Power.
    • Under certain conditions the control module commands the engine OFF.

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 Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Record the throttle actuator control (TAC) module calibration with a scan tool.

Does the TAC module calibration match the part number of the TAC module?

--

Go to Step 3

Go to Step 11

3

Observe the DTC Information with a scan tool.

Is DTC P2120, P2125, or P2138 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 4

4

  1. Turn OFF the ignition for 30 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the APP Sensors 1 and 2 parameter with a scan tool.

Does the scan tool indicate that the APP sensors 1 and 2 parameters disagree?

--

Go to Step 5

Go to Testing for Intermittent Conditions and Poor Connections

5

  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor.
  3. Disconnect the TAC module.
  4. Measure the resistance of the following circuits for each of the APP sensors with a DMM:
  5. • The low reference circuit
    • The signal circuit
    • The 5-volt reference circuit

Is the resistance more than the specified value for any circuit?

5 ohms

Go to Step 9

Go to Step 6

6

Test the signal circuit of the APP sensor 1 for a short to the signal circuit of the APP sensor 2. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

Test for an intermittent and for a poor connection at the TAC module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

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.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9

Repair the high resistance in the circuit that measured above the specified value. Refer to Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 12

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10

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

Did you complete the replacement?

--

Go to Step 12

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11

Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

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12

  1. Assemble the vehicle, as necessary.
  2. Clear the DTCs with a scan tool.
  3. Start the engine.
  4. Operate the system in order to verify the repair.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13

Important: Be aware that repairing one individual condition may correct more than one DTC.

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK