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 P0068: Throttle Body Airflow Performance
DTC P0121: Throttle Position (TP) Sensor 1 Performance

### Circuit/System Description

The engine control module (ECM) uses the following information to calculate an expected airflow rate:

• | The throttle position (TP)

• | The barometric pressure (BARO)

• | The manifold absolute pressure (MAP)

• | The intake air temperature (IAT)

• | The engine RPM

• | The mass air flow (MAF)

### Conditions for Running the DTC

• | DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.

• | The engine is running and the engine speed is more than 600 RPM.

• | DTC P0068 and P0121 run continuously when the above conditions are met.

### Conditions for Setting the DTC

The ECM detects that the airflow rate is more than the calculated airflow for more than 0.2 second.

### Action Taken When the DTC Sets

• | DTC P0068 is a Type A DTC.

• | DTC P0121 is a Type B DTC.

• | The control module commands the TAC system to operate in the Reduced Engine Power mode.

• | A message center or an indicator displays Reduced Engine Power.

• | Under certain conditions the control module commands the engine OFF.

### Conditions for Clearing the MIL/DTC

• | DTC P0068 is a Type A DTC.

• | DTC P0121 is a Type B DTC.

### 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

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Testing

1. Inspect for the following conditions:

• | Vacuum hoses for splits, kinks, and proper connections

• | Inspect thoroughly for any type of leak or restriction

• | Air leaks at throttle body mounting area and intake manifold sealing surfaces

2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.

⇒ | If more than 4 volts or less than 0.8 volt, refer to DTC P0106 .

3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change as engine speed is increased and returned to idle.

⇒ | If the MAP sensor kPa does not change refer to DTC P0106 .

4. Take a snapshot of the engine data list while performing the actions listed below. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.

• | Idle the engine.

• | Increase the engine speed slowly to 3,000 RPM, then back to idle.

• | Exit from the snapshot and review the data.

• | Observe the MAF Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle .

⇒ | If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101 .

5. Inspect the throttle body for the following conditions:

• | Loose or damaged throttle blade

• | Broken throttle shaft

• | Any throttle body damage

⇒ | If any of these conditions exist, replace the throttle body assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Throttle Body Assembly Replacement

• | Control Module References for ECM replacement, setup, and programming.