Diagnostic Instructions

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

P2100

P2119

Conditions for Setting the DTC

P0638

P2100

The ECM detects the output circuit for the TAC motor is open, shorted to ground, or shorted to a voltage. The condition exists, then a 5 second delay for MIL ON.

P2101

The ECM detects a 4-50 percent difference between the commanded and the actual throttle plate position, dependant upon the rate of commanded throttle movement. The condition exists, then a 5 second delay for MIL ON.

P2119

The ECM determines that the throttle valve did not return to the rest position within 500 mS. The condition exists, then a 5 second delay for MIL ON.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

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

Component Connector End Views

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

Control Module References for scan tool information

Special Tools

J 34730-405 Injector Test Lamp

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify DTC P0121, P0122, P0123, P0221, P0222, or P0223 is not set.

⇒	If a DTC is set refer to DTC P0121, P0122, P0123, P0221, P0222, or P0223 for further diagnosis.

2. Observe the scan tool TP sensor parameters. Verify that TP sensor 1 voltage is between 3.02-4.00 V, and TP sensor  2 voltage is between 1.00-1.86 V.

⇒	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.

⇒	If a DTC 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. DTC P0638, P2100, P2101, or P2119 should not set.

⇒	If a DTC 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 you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Inspect the throttle body for the following conditions:

•	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.

Note: 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 4.0-5.0 V between the TAC motor control 1 circuit terminal B and ground.

⇒	If voltage is 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 voltage is less than the specified range, test the motor control 1 circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Connect a test lamp between the TAC motor control 2 circuit terminal A and B+. The test lamp should NOT illuminate.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

5. Test for greater than 3.5 V between TAC motor control 1 circuit terminal B and TAC motor control 2 circuit terminal A.

⇒	If the voltage is less than the specified value, test the motor control 2 circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

6. 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 and then turns OFF.

⇒	If the injector test lamp does not illuminate, replace the ECM.

7. If all circuits test normal, replace the throttle body.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.