P1551
DTC P1551
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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 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 greater 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 10 percent or greater than 40 percent 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 30 percent. This is referred to as the rest position. The throttle valve should not be completely closed, nor should it 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 (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Engine Control Module Description (Engine Control Module Description)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0121, P0122, P0123, P0221, P0222, P0223, P2100, P2101, or P2119 is not set.
• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) for further diagnosis.
2. Start the engine. Observe the DTC information with a scan tool for 30 seconds. DTC P1551 should not set.
3. 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 (Verification Tests) after completing the diagnostic procedure.
Throttle Body Assembly Replacement (Removal and Replacement)