What it means
The B channel of the throttle or pedal position sensor reports values that do not correlate with the A channel or with engine load. Often caused by mechanical wear in the resistive track or by a sticking pedal/throttle plate.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The PCM evaluates the throttle or accelerator-pedal position sensor B signal for a plausible range and response as the throttle or pedal moves. P0221 sets when the B reading behaves outside the expected range or performance pattern, which can reflect sensor wear or restricted movement.
Common causes
Most likely first.
- Resistive track worn
- Throttle plate sticking
- Sensor element aged beyond calibration window
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Record freeze-frame data and check for related throttle, pedal, or correlation codes to establish the conditions when the B reading became implausible.
- Graph live data for sensor B while slowly moving the pedal or throttle and compare its progression with available related position and engine-load data.
- Inspect the pedal or throttle mechanism for sticking or obstruction, and check the B sensor connector and harness for damage or poor contact.
- Check that the B signal changes smoothly through its travel and compare readings with the manufacturer’s specification.
- If the signal remains out of range, test the sensor and circuit using the manufacturer’s diagnostic procedure before replacing components.
Common fixes
- Remove an obstruction or correct sticking in the pedal or throttle mechanism.
- Repair a loose connector or damaged sensor B wiring.
- Replace the worn or out-of-calibration throttle or pedal position sensor B if testing confirms it.
- Perform any manufacturer-specified adjustment or relearn after repair.
Can I keep driving?
Avoid fast traffic and heavy acceleration if throttle response hesitates, surges, or enters a reduced-power mode. The fault can make acceleration inconsistent and may leave you without the response needed to merge safely.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.