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 Descriptor

DTC P1551: Throttle Valve Rest Position Not Reached During Learn

### 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 DTC

• | The accelerator pedal position (APP) is less than 13 percent.

• | DTC P1551 runs when the throttle actuator control motor is deactivated.

### Conditions for Setting the DTC

The ECM detects the TP sensor angle is less than 1.8 percent or greater than 13.1 percent for greater than 4 seconds, when the throttle actuator control motor is deactivated.

### Action Taken When the DTC Sets

DTC P1551 is a type A DTC.

### Conditions for Clearing the DTC

DTC P1551 is a type A DTC.

### Diagnostic Aids

• | Operating the throttle valve with the Throttle Position control function of the scan tool may cause additional DTCs to set. DO NOT attempt to diagnose DTCs set during this function.

• | Inspect for a condition in which the throttle valve may have been held open.

• | Inspect for conditions in which ice may have formed in the throttle bore.

• | The throttle valve is spring loaded to a slightly open position. The throttle valve should be open approximately 3-5 percent. This is referred to as the rest position. The throttle valve should not be completely closed, nor should they be open any greater than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure.

### 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, P0223, P1551, or P2119 should not set.

⇒ | If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. 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

Ignition OFF, disconnect the air intake duct at the throttle body and inspect for the following:

• | Throttle valve that is NOT in the rest position

• | Throttle valve that is binding open or closed

• | Throttle valve that is free to move open or closed WITHOUT spring pressure

⇒ | If a condition is found, 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