GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Terrain 🢒 DTC 🢒 DTC P0638, P2100, P2101, or P2119

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptors

DTC P0638: Throttle Actuator Control (TAC) Command Performance

DTC P2100: Throttle Actuator Control (TAC) Motor Control Circuit

DTC P2101: Control Module Throttle Actuator Position Performance

DTC P2119: Throttle Closed Position Performance

Circuit/System Description

The engine control module (ECM) controls the throttle valve by applying a varying voltage to the control circuits of the throttle actuator control (TAC) motor. The ECM monitors the duty cycle that is required to actuate the throttle valve. The ECM monitors the throttle position (TP) sensors 1 and 2 to determine the actual throttle valve position.

Conditions for Running the DTCs

P0638

    • The ignition is ON.
    • The DTC runs continuously once the above condition is met for more than 1 second.

P2119

    • The engine is operating.
    • The DTC runs continuously once the above condition is met for more than 1 second.

Conditions for Setting the DTC

P0638

    • The ECM detects that the commanded duty cycle for the range test high is more than 80 percent for more than 0.6 second.
        OR
    • The ECM detects that the commanded duty cycle for the range test low is more than 80 percent for more than 5 seconds.

P2119

The ECM determines that the throttle valve did not return to the rest position within 560 milliseconds.

Action Taken When the DTC Sets

DTCs P0638 and P2119 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P0638 and P2119 are Type A DTCs.

Diagnostic Aids

Inspect for a condition in which the throttle valve may have been held open. For example, ice may have formed in the throttle bore causing the throttle valve not to close.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module Connector End Views

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. Ignition ON, observe the scan tool DTC information parameter. Verify DTCs P0121, P0122, P0123, P0221, P0222, or P0223 are not set.
    2. ⇒If any of the DTCs are set, refer to DTC P0121, P0122, P0123, P0221, P0222, P0223, or P2135 for further diagnosis.
  2. Verify the scan tool TP sensor 1 voltage parameter and the scan tool TP sensor  2 voltage parameter are between 0.4-0.9 volts.
    3. ⇒If not within the specified range, refer to DTC P0121, P0122, P0123, P0221, P0222, P0223, or P2135 for further diagnosis.
  3. Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release the pedal. Repeat the procedure several times. DTCs P0638 or P2119 should not set.
    4. ⇒If any of the DTCs P0121, P0122, P0123, P0221, P0222, or P0223 set while performing this procedure go to DTC P0121, P0122, P0123, P0221, P0222, P0223, or P2135 for further diagnosis.
  4. Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times. DTCs P0638 or P2119 should not set.
    5. ⇒If any of the DTCs P0121, P0122, P0123, P0221, P0222, or P0223 set while performing this procedure, refer to DTC P0121, P0122, P0123, P0221, P0222, P0223, or P2135 for further diagnosis.
  5. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing
  1. Inspect the throttle body for the following conditions:
    2. • A throttle blade that is not in the rest position
    • A throttle valve that is binding open or closed
    • A throttle valve that opens or closes without spring pressure
    ⇒If a condition is found, replace the throttle body.

    Important: Disconnecting the throttle body harness connector causes additional DTCs to set.

  2. Ignition OFF, disconnect the harness connector at the throttle body.
  3. Ignition ON, test for 2-4.5 volts on the motor control 1 and motor control 2 circuits.
    4. ⇒If greater than the specified range, test the appropriate motor control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
    ⇒If less than the specified range, test the appropriate motor control circuit for a short to ground or an open. If the circuit tests normal, replace the ECM.
  4. Ignition OFF, disconnect the ECM connector X2. Test for continuity between Motor Control 1 circuit and Motor Control 2 circuit.
    5. ⇒If continuity exists between the circuits, repair the short between those circuits. If the circuit tests normal, replace the ECM.
  5. If all circuits test normal, test or replace the throttle body.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Throttle Body Assembly Replacement
    •  Control Module References for engine control module replacement, setup, and programming