P0221 Code: Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance

What the P0221 code means

Electronic throttle systems carry two sensors in the pedal and two in the throttle body. Sensor B is the second of that pair, and its job is to let the computer verify what the first one reports.

The P0221 code does not mean an impossible voltage like P0222 or P0223, or a contradiction between the two signals like P2135. It means something more subtle: the signal is within range but its behavior is not what is expected.

In practice that means sudden jumps, zones where the reading does not change even though the pedal is moving, or a progression that does not match the one from sensor A.

The typical cause lies in how these sensors wear out. Potentiometer types have a resistive track with a contact sliding over it, and that contact spends most of its time in the same zone: the rest position. Over the years the track wears right there, and dead spots show up in the first part of the travel, which is exactly the part used the most while driving.

It helps to understand why this code usually starts out intermittent. While the worn zone of the track is small, the contact crosses it so fast that the computer does not always manage to register the problem, and the driver only feels an isolated jerk and blames something else. As the zone grows, the interruptions get longer and more frequent until the system classifies them as a permanent fault. That pattern of steady worsening is characteristic and helps tell it apart from a connector problem, which tends to come and go without following any trend.

One tip that helps you decide: check whether the fault also shows up when you press the pedal extremely gently, hardly moving it. Track wear is concentrated in the first few millimeters (a small fraction of an inch) of travel, so a clean progression through the middle and upper range with jumps only at the start confirms the diagnosis with no further testing.

P0221 code symptoms

• Limp mode with limited power.
• Check engine light on.
• Uneven pedal response, with jerks or zones with no reaction.
• Unsteady idle.
• The fault shows up mostly in the first part of the pedal travel.
• Erratic shifting on automatic transmissions.
• The symptom can be intermittent at first and become permanent over time.
• The progression is clean in the middle and upper range, with jumps only in the first few millimeters.

Likely causes of the P0221 code

1. Potentiometer track worn in the rest zone. The most frequent cause on sensors with years of use.
2. Connector with backed-out or dirty pins.
3. Sensor ground with high resistance.
4. Wiring rubbed along its route to the computer.
5. Moisture or liquid getting in on the sensor.
6. Weakened pedal spring, which does not bring the contact back to its exact position.
7. Replacement sensor of lower quality, with a different curve from the original.
8. Unstable reference voltage.

How to diagnose the P0221 code step by step

1. Watch the signal in live data while you press the pedal very slowly. It should rise progressively and continuously, with no jumps or flat stretches.
2. Pay attention to the first part of the travel, which is where wear shows up most often.
3. Compare both signals, A and B, at the same time. Their relationship should stay constant through the whole travel.
4. Check the sensor ground by measuring its voltage drop.
5. Inspect the connector for backed-out pins and moisture.
6. Move the harness with the key on while watching the reading.
7. Verify that the pedal returns firmly to its rest position.
8. Check that the five volt reference is stable.
9. Press the pedal extremely gently through the first few millimeters. Jumps only there, with a clean progression everywhere else, confirm track wear.

How to fix the P0221 code

• Replace the pedal sensor when its signal shows dead spots or jumps in the travel, because track wear cannot be repaired.
• Clean the connector and replace the terminals with backed-out pins.
• Repair the sensor ground down to bare metal.
• Fix damaged wiring with solder and suitable protection.
• Dry the area if liquid got in.
• Use a replacement from a recognized manufacturer, because cheap ones have different curves.
• Replace the whole pedal assembly when the jumps are concentrated in the first part of the travel, because the wear of the track has no repair.

After the replacement, run the throttle relearn if the vehicle calls for it and check that the signal sweeps its whole range continuously.

Technical reference data

• Typical signal at rest: between 0.5 and 0.9 volts. Wide open: between 3.8 and 4.7 volts.
• The progression should be continuous, with no jumps or stretches where the reading does not change.
• Wear concentrates in the rest zone, where the contact spends the most time.
• Allowable voltage drop on the ground: below 0.2 volts.
• P0222 means low voltage and P0223 means high voltage on the same circuit.
• Wear concentrates in the first few millimeters of travel, where the contact spends the most time.

Brand-specific notes

The characteristic symptom of this code is a fault that starts out intermittent and gradually becomes permanent. That fits progressive track wear: at first it only fails when the contact crosses the worn spot, and over time that zone widens.

The definitive test is to watch the signal while pressing the pedal very slowly, millimeter by millimeter. A stretch where the reading sits still while your foot keeps going down confirms the wear without taking anything apart.

Frequently asked questions about P0221