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 provide 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 vehicle speed is 0 km/h (0 mph).

• | The engine speed is less than 40 RPM.

• | The engine coolant temperature (ECT) is between 5-100°C (41-212°F).

• | The intake air temperature (IAT) is between 5-143°C (41-290°F).

• | The ignition 1 voltage is more than 10 volts.

• | The accelerator pedal position (APP) is less than 15 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 2 percent or more than 13 percent for more than 4 seconds or for a cumulative of 50 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.

• | The scan tool has the ability to operate the throttle actuator control system using Special Functions. This function operates the throttle through the entire range in order to determine if the throttle body and system operate correctly.

• | 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 more 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

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0121, P0122, P0123, P0221, P0222, P0223, P2100, P2101, or P2119 are not set.

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

2. Observe the DTC information with a scan tool for 30 seconds. DTC P1551 should not set.
3. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### 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