Diagnostic Instructions
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 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 2 percent or greater than 13 percent for greater 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 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
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe the scan tool DTC information. Verify that DTCs P0121, P0122, P0123, P0221, P0222, P0223, P2100, P2101, or P2119 are not set.
- Observe the scan tool DTC information for 30 seconds. DTC P1551 should not set.
- 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 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
