The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the accelerator pedal position. The APP sensors 1 and 2 are located within the pedal assembly. Each sensor has the following circuits:

Two processors are also used to monitor the TAC system data. Both processors are located within the engine control module (ECM). Each signal circuit provides both processors with a signal voltage proportional to pedal movement. Both processors monitor each other's data to verify that the indicated APP calculation is correct.

The voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 2 seconds.

DTC P2138 is a Type A DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.84-4.82 volts and change with accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensor 2 voltage parameter. The reading should be between 0.66-4.82 volts and change with accelerator pedal input.
3. Ignition ON, observe the scan tool APP Sensor 1 and 2 parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
5. Verify that DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 are set:

⇒	If DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 are set, refer to DTC P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 .

1. Ignition OFF, disconnect the accelerator pedal harness connector at the accelerator pedal. Allow sufficient time for the ECM to power down.
2. Test for less than 3 ohms of resistance between each low reference circuit terminals A and D and ground.

⇒	If greater than 3 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between each 5-volt reference circuit terminals C and F and ground.

⇒	If less than 4.8 volts, test affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the control module.

⇒	If greater than 5.2 volts, test affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.

4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.

⇒	If greater than 0.1 volts, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1, and verify the APP sensor 1 voltage is greater than 4.8 volts.

⇒	If less than 4.8 volts, test the APP sensor 1 signal circuit for an open, or short to ground. If the circuit tests normal, replace the control module.

6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2, and verify that the APP sensor 2 voltage is greater than 4.8 volts.

⇒	If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance, or short to ground. If the circuit tests normal, replace the control module.

7. Ignition OFF, disconnect the harness connector at the ECM.
8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:

•	The ECM C2 signal circuit terminal 15 to APP terminal E

•	The ECM C2 signal circuit terminal 34 to APP terminal D

•	The ECM C2 5-volt reference circuit terminal 48 to APP terminal C

•	The ECM C2 5-volt reference circuit terminal 49 to APP terminal F

⇒	If greater than 5 ohms, repair the affected circuit.

9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.

⇒	If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuit.

10. If all circuits test normal, replace the accelerator pedal.

Important: Circuit/System Testing must be performed before proceeding with Component Testing.

Dynamic Test

1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the signal terminal and the low reference terminal with a DMM. the voltage should vary between 0.66-4.82 volts with out any spikes or dropouts.

⇒	If the voltage is not within the specified range or is erratic, replace the accelerator pedal assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.