For 1990-2009 cars

### 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 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 greater than 1 second.

#### P2119

• | The engine is running.

• | The DTC runs continuously once the above condition is met for greater than 1 second.

### 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 0.6 second.

| OR

• | The ECM detects that the commanded duty cycle for the range test low is greater than 80 percent for greater 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

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

### Circuit/System Verification

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

⇒ | If any 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 TP sensor 2 voltage parameter is between 0.4-1.0 volts.

⇒ | 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.

⇒ | If 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.

⇒ | If 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. 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.

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

2. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the throttle body.
3. Install the MAIN fuse. Ignition ON, test for 2-4.5 volts on each motor control circuit and ground.

⇒ | 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.

⇒ | 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.

4. Ignition OFF, disconnect the ECM connector X2. Test for continuity between Motor Control 1 circuit terminal 6 and Motor Control 2 circuit terminal 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