Throttle/Petal Position Sensor/Switch B Circuit Malfunction
The engine's computer detected a problem with the secondary throttle position sensor (Sensor B), which tells it how much the driver is asking for power. It's like a broken gas pedal signal—the engine doesn't know how much fuel to inject.
The ECM monitors Throttle Position Sensor B (typically on dual-throttle systems) for voltage signals that correlate with pedal position. It compares the signal against expected ranges and checks for consistency with Sensor A. Out-of-range voltage, slow response, or cross-sensor mismatch triggers the fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| TPS B Voltage | 0.5–4.5V proportional to pedal | <0.5V or >4.8V, or stuck position |
| Sensor A vs B Correlation | <5% deviation between sensors | >10% deviation or timeout |
Code P0221 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0221 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.