GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 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 provides 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

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

Motor Control 1

P2100, P2101

P2100, P2101, P2119

P2100, P2101, P2119

P0123, P2101

P0638, P2101, P2119

Motor Control 2

P2100, P2101, P2119

P2100, P2101

P2100, P2101, P2119

P2101

P0638, P2101, P2119

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 and P2101

    • The ignition is ON or the engine is operating.
    • The ignition voltage is greater than 7 volts.
    • Throttle position adaptation is not active.
    • DTCs P0638 and P2101 run continuously once the above conditions are met for greater than 1 second.

P2100

    • Before the ECM can report DTC P2100 failed, DTC P0638 must run and pass.
    • The ignition is ON or the engine is operating.
    • DTC P2100 runs continuously once the above conditions are met for greater than 1 second.

P2119

    • The ignition is ON.
    • The vehicle speed is 0 km/h (0 mph).
    • The engine speed is less than 40 RPM.
    • The engine coolant temperature (ECT) is 5-85°C (41-185°F).
    • The intake air temperature (IAT) is 5-60°C (41-140°F).
    • The ignition voltage is greater than 10 volts.
    • The accelerator pedal position (APP) is less than 15 percent.
    • DTC P2119 runs once per ignition cycle when the above conditions are met for greater than 560 milliseconds.

Conditions for Setting the DTC

P0638

    • The ECM detects that the commanded duty cycle for the range test high is greater than 80 percent for greater than 4 seconds, or for a cumulative of 50 seconds.
        OR
    • The ECM detects that the commanded duty cycle for the range test low is greater than 80 percent for greater than 4 seconds, or for a cumulative of 50 seconds.

P2100

    • The ECM detects the output driver for the TAC motor does not deactivate when commanded OFF.
    • The condition exists for 4 seconds.

P2101

    • The ECM detects that the difference between the commanded and the actual throttle plate position is greater than 4 percent, or up to 50 percent depending on the rate at which the throttle position changes.
    • The condition exists for 4 seconds, or for a cumulative of 50 seconds.

P2119

The ECM determines that the throttle valve did not return to the rest position. The condition exists for greater than 4 seconds.

Action Taken When the DTC Sets

DTCs P0638, P2100, P2101, and P2119 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P0638, P2100, P2101, and P2119 are Type A DTCs.

Diagnostic Aids

The following table illustrates the ECM connector locations:

ECM Connector Location

X2

X1

Front of Vehicle

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

Component 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

Control Module References for scan tool information

Special Tools

J 34730-405 Injector Test Lamp

Circuit/System Verification
  1. Ignition ON, observe the scan tool DTC information. 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, or P0223 for further diagnosis.
  2. Verify the scan tool TP sensor 1 voltage parameter is between 3.24-3.54 volts, and TP sensor  2 voltage parameter is between 1.36-1.86 volts.
    3. ⇒If either TP sensor voltage is not within the specified range refer to DTC P0121, P0122, P0123, P0221, P0222, or P0223 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, P2100, P2101, or P2119 should not set.
    4. ⇒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, or P0223 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, P2100, P2101, 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, or P0223 for further diagnosis.
  5. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. 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 of the throttle body.
  3. Ignition ON, test for 4.0-4.1 volts between the TAC motor control 1 circuit terminal 5 and ground.
    4. ⇒If greater than the specified range, test each of the motor control circuits for a short to voltage. If the circuits tests normal, replace the ECM.
    ⇒If less than the specified range, test the motor control 1 circuit for an open/high resistance. Test each of the motor control circuits for a short to ground. If the circuits tests normal, replace the ECM.
  4. Test for greater than 3.5 volts between TAC motor control 1 circuit terminal 5 and TAC motor control 2 circuit terminal 3.
    5. ⇒If less than the specified value, test the motor control 2 circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  5. Ignition OFF, connect the J 34730-405 injector test lamp between the TAC motor control 1 and TAC motor control 2 circuits of the throttle body harness connector. Observe the injector test lamp while turning the ignition ON for 5 seconds and then OFF. Verify the injector test lamp illuminates brightly.
    6. ⇒If the injector test lamp does not illuminate, replace the ECM.
  6. If all circuits test normal, 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