P2173 - Throttle Actuator Control System High Air Flow Detected
The P2173 code indicates that the engine control module (ECM) has detected a higher than expected airflow into the engine while the throttle plate is in a closed or near-closed position. This typically points to a vacuum leak downstream of the throttle body, a stuck or malfunctioning throttle plate, or a faulty throttle position sensor. The ECM uses the throttle actuator control system to regulate idle speed and airflow; when actual airflow exceeds the commanded amount, it sets this code.
1. Most Common Causes
- Vacuum leak in the intake duct or seals downstream of the throttle body (unmetered air entering the engine)
- Contaminated, disconnected, or faulty MAF sensor reporting a higher airflow than actual
- Throttle body with a defective or damaged actuator that fails to close the throttle plate to the commanded position
- Accelerator pedal position (APP) sensor or throttle position (TPS) sensor with erroneous, misaligned, or shorted signals
- Excessive carbon buildup on the throttle plate or bore interfering with precise airflow control
- Wiring or connector faults in the throttle actuator circuit (open circuit, short to ground/power, or abnormal resistance)
- PCM with outdated calibration or internal control module failure
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or high idle speed
- Reduced engine power or hesitation on acceleration
- Poor fuel economy
- Possible stalling
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data. Check for additional codes like P0121, P0221, etc.
Step 2: Visually inspect vacuum hoses, intake manifold gaskets, and PCV system for leaks. Use a smoke machine if available.
Step 3: Check throttle body for carbon buildup; clean if necessary. Inspect throttle plate movement for binding.
Step 4: Test throttle position sensor and accelerator pedal position sensor with a multimeter or scan tool for proper voltage signals.
Step 5: Check throttle actuator control motor and wiring for shorts or opens. Perform relearn procedure if repairs are made.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the vehicle may experience reduced power, stalling, or erratic idle, which can be dangerous. Have it diagnosed promptly.
How much does it cost to fix?▼
The cost varies depending on the cause. Cleaning the throttle body may cost $50-$100, while replacing a throttle position sensor or actuator can range from $100-$300. A vacuum leak repair may be $50-$150.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.