Throttle/Pedal Position Sensor B Range/Performance
Diagnostic trouble code P0221 indicates that the Powertrain Control Module (PCM) has detected an unexpected voltage or resistance from the Throttle/Pedal Position Sensor/Switch 'B' circuit. The PCM sets this code when the signal from sensor 'B' does not correlate with the expected range or the signal from sensor 'A', suggesting a performance issue with the sensor or its circuit.
This code is considered high severity because a faulty throttle position sensor can cause unpredictable engine behavior, sudden loss of power, or force the vehicle into a restricted 'limp mode', making it unsafe to drive.
Common symptoms
- Illuminated Check Engine Light
- Engine hesitation or stumbling upon acceleration
- Vehicle stuck in 'limp home' mode with limited speed
- Rough or erratic engine idle
- Poor overall engine performance and lack of power
Likely causes
- Defective Throttle Position Sensor (TPS) or Pedal Position Sensor
- Corroded, damaged, or loose electrical connections at the sensor
- Damaged or shorted wiring in the sensor 'B' circuit
- Dirty or binding electronic throttle body
- Incorrectly adjusted throttle position sensor (on older models)
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the wiring and connectors for the Throttle/Pedal Position Sensor 'B'.
Look for: Look for frayed wires, melted insulation, corrosion on the pins, or loose connectors that could cause an intermittent or poor connection.
Use a scan tool to monitor the live data for Throttle Position Sensor 'A' and 'B' voltages while slowly pressing the accelerator pedal.
Look for: The voltage for sensor 'B' should increase or decrease smoothly without any dropouts or spikes, and it should correlate properly with sensor 'A' (often one goes up while the other goes down, or they move in parallel depending on the design).
Test the 5-volt reference and ground circuits at the sensor connector using a digital multimeter.
Look for: You should see a steady 5 volts on the reference wire and near 0 ohms of resistance on the ground wire with the key on, engine off.
Inspect and clean the electronic throttle body.
Look for: Check for excessive carbon buildup or physical binding of the throttle plate that could prevent smooth operation and cause the sensor readings to fall out of the expected range.
Perform a sweep test on the sensor itself using a multimeter or oscilloscope if the scan tool data was inconclusive.
Look for: Look for any glitches, dead spots, or sudden drops in resistance/voltage as the sensor is manually swept through its full range of motion.
This page explains the generic P0221 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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