P0221 - Throttle/Pedal Position Sensor/Switch 'B' Circuit Range/Performance Problem
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0221 is set when the Engine Control Module (ECM) detects that the signal voltage from throttle/pedal position sensor 'B' is outside the expected range or is not correlating correctly with sensor 'A'. In electronic throttle control (ETC) systems, dual sensors are used for safety redundancy. If the sensor output shows an erratic voltage sweep or a steady voltage that doesn't match the throttle blade's physical position or the other sensor's output, the ECM triggers limp mode to prevent unintended acceleration.
Possible Causes
Faulty throttle body assembly or worn sensor tracks
Carbon buildup or dirt causing the throttle plate to bind
Wiring harness damage or poor connection (corrosion at connectors)
Faulty accelerator pedal assembly
Internal Engine Control Module (ECM) failure
Symptoms
Recommended Solution
- Visual Inspection: Check the throttle body connector for corrosion, backed-out pins, or moisture. Clean with contact cleaner.
- Mechanical Check: Inspect for carbon deposits inside the throttle bore. Clean using dedicated throttle body cleaner.
- Electrical Testing: Verify 5V reference and ground. Use an oscilloscope to monitor the signal wire for 'glitches' or 'dead spots' while slowly moving the throttle blade/pedal.
- Live Data: Observe Sensor A and B voltages on a scanner; they should move smoothly and remain in a set ratio.
- Replacement & Calibration: Replace throttle body or pedal assembly. Note: Most modern cars require a 'Throttle Linkage/Idle Relearn' procedure using a scan tool after replacement.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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