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P0221 — Throttlepedal Position Sensorswitch B Circuit Rangeperformance

Generic OBD-II · all makesPowertrain (engine & transmission)

P0221 indicates the engine control module has detected a range or performance problem with the B circuit of the throttle or accelerator position sensor. This means the sensor B signal voltage is outside expected parameters or does not correlate properly with the companion A circuit. The code may trigger reduced engine power as a fail-safe precaution.

Symptoms

What causes it — most likely first

1. Faulty throttle or accelerator position sensor B

The internal potentiometer or circuit for the B signal can wear out or drift, producing a voltage outside the expected range or that fails to correlate with the A signal.

2. Wiring or connector fault in the B circuit

Damaged, chafed, or moisture-corroded wires can create opens, shorts, or high resistance in the signal, reference, or ground paths.

3. Loose or corroded sensor connector

Poor pin contact at the sensor harness connector can cause intermittent voltage drops or noise interpreted as a range or performance error.

4. Throttle plate binding or carbon buildup

Mechanical sticking of the throttle blade can cause a mismatch between actual throttle angle and sensor voltage, setting a performance fault even if the sensor is electrically sound.

5. PCM internal or software fault

A rare control module fault may misinterpret a valid sensor signal; this should only be considered after the sensor, wiring, and mechanical systems are verified good.

How it's diagnosed

  1. Visually inspect the sensor and connector for corrosion, damaged pins, or loose terminals.
  2. Check for related codes and review freeze-frame data to see operating conditions when the fault set.
  3. Monitor the B circuit sensor voltage with a scan tool or multimeter while slowly actuating the pedal or throttle to verify smooth progression.
  4. Test the wiring between the sensor and PCM for continuity, shorts to ground, and shorts to voltage.
  5. Compare sensor A and sensor B signals to confirm they correlate; replace the sensor if the B track is skewed or erratic.
  6. Inspect the throttle plate and bore for carbon buildup or mechanical binding if electrical tests are normal.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0219 — Engine Overspeed ConditionP0220 — Throttlepedal Position Sensorswitch B P0222 — Throttlepedal Position Sensorswitch B P0223 — Throttlepedal Position Sensorswitch B P0224 — Throttlepedal Position Sensorswitch B P0225 — Throttlepedal Position Sensorswitch C

Frequently asked

Should I replace the PCM to fix P0221?

No. A failed PCM is an uncommon cause of this code. Most instances are resolved by repairing wiring or replacing the throttle or accelerator position sensor. The PCM should only be suspected after the sensor, connectors, and wiring have been thoroughly tested and ruled out.

Can a dirty throttle body cause P0221?

Yes. Excessive carbon buildup or a binding throttle plate can create a mismatch between sensor voltage and actual throttle angle, triggering a performance fault. Cleaning and verifying smooth operation is a valid diagnostic step.

Do I need to replace the entire throttle body?

It depends on the vehicle. Some designs allow the position sensor to be replaced separately, while others use an integrated assembly. Consult the specific service information to determine the correct repair procedure.

Why does the engine go into limp mode with this code?

The PCM enters fail-safe mode to limit engine speed and prevent unintended acceleration when it detects an unreliable throttle position signal. This protects the engine and drivetrain until the fault is corrected.