P0221 Code: Throttle/Pedal Position Sensor B Range/Performance
The second throttle angle signal leaves its window or stops following the plate, so power is cut back.
At a glance
Severity: Moderate
- Meaning
- Throttle/Pedal Position Sensor B Range/Performance
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $80–$850
- DIY difficulty
- Moderate
Electronic throttle bodies carry two angle sensors, A and B, reading the same throttle shaft. Sensor B usually runs in the opposite direction to A or with a fixed offset, so the PCM always knows what B should read for any plate angle. P0221 sets when sensor B is electrically alive but its value sits outside the window allowed for the current position, jumps, or lags when the throttle motor moves the plate. Unlike P2135, which only says the two signals disagree, P0221 means the PCM has decided that B in particular is the implausible one. Because throttle angle is a safety input, the PCM usually limits throttle opening until the fault is gone.
Can I keep driving? The car normally stays drivable in reduced-power mode, but acceleration is weak and merging onto a highway can be risky. Drive gently to a shop, and don't rely on the car for towing or long trips until it's fixed.
How to read P0221
- P Powertrain
- 0 Generic (SAE)
- 2 Fuel & air (injector circuit)
- 21 Specific fault
Symptoms
- Reduced power or limp mode, sometimes with a 'reduced engine power' message
- Idle held at a fixed, higher speed such as 1,200 to 1,500 rpm
- Delayed or flat response when you press the accelerator
- Stalling or a dip in idle when coming to a stop
- Warning appears after a bump or a car wash and clears after a restart
- EPC or wrench lamp on some makes in addition to the check engine light
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Sensor B inside the throttle body worn, contaminated or failing (resistive track or Hall element)
- Fretting or corrosion on the sensor B signal pin in the throttle body connector
- Throttle plate or its nylon gear train binding, so the plate doesn't reach the angle the PCM expects
- Damaged sensor B signal wire between the throttle body and the PCM
- Throttle adaptation not performed after cleaning, battery disconnect or replacement
- Wrong or low-quality replacement throttle body, or a PCM input fault
Diagnosis step by step
Check which throttle codes appear together
P0221 alone points at sensor B or its signal wire. If P0121 and P0221 appear together, suspect something both share, such as the plate, the reference or the ground. With P2101, the throttle motor or a sticking plate is the more likely root cause.
Tools: OBD-II scanner
Read sensor B at rest with key on, engine off
Look up the closed-throttle specification for sensor B; it's typically near one end of the scale on inverse designs or a volt or two above sensor A on offset designs. A value that sits outside the specified window at rest, or drifts while you watch, points to the sensor itself.
Tools: OBD-II scanner
Command the throttle and watch sensor B follow
Use your scan tool's throttle actuator test to step the plate through several angles, or press the pedal slowly with the engine off. Sensor B should track the commanded angle smoothly within a fraction of a second; a step, flat spot or delay pins down a worn sensor or a binding plate.
Tools: OBD-II scanner
Inspect the plate and gear train
With the ignition off and intake duct removed, check that the plate moves freely against its spring and returns to its default position. Heavy carbon at the plate edge or a gritty feel from the gear train means the PCM sees the plate lag behind its command.
Tools: Flashlight, Screwdriver
Back-probe the B signal while tapping the throttle body
With the engine idling, back-probe the sensor B signal wire at the connector and lightly tap the throttle body and flex the harness. A meter or scope reading that flickers identifies an intermittent pin or wire that a static check misses.
Tools: Multimeter
Repair, then run the throttle relearn
Most throttle bodies have non-serviceable sensors, so a failed sensor B means a new throttle body. After cleaning or replacement, run the idle and throttle relearn in the correct order; skipping it can set P0221 again right away.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean the throttle body and perform the relearn | Yes | $80–$200 |
| Repair throttle body connector terminals or pigtail | Yes | $100–$280 |
| Repair sensor B signal wire | No | $150–$380 |
| Replace electronic throttle body and relearn | Yes | $300–$850 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Volkswagen
On VW drive-by-wire throttle bodies the two angle sensors are part of the throttle control unit, and P0221 usually brings on the EPC lamp. After cleaning the throttle body or disconnecting the battery, the throttle adaptation must be run with a suitable scan tool, or the code can return immediately.
Field data
| Chevrolet | 4 | Traverse |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
With the check engine light on, P0221 fails an OBD-II emissions inspection. After repairs, clear the code and complete several drive cycles so the readiness monitors are complete before the test.
Frequently asked questions
How is P0221 different from P2135?
P2135 only reports that sensors A and B disagree with each other. P0221 means the PCM has concluded that sensor B specifically reads outside its plausible range or doesn't follow the plate, which narrows the search to the B signal and its wiring.
Can I replace only the sensor B part?
On most modern throttle bodies, no. Both sensors are sealed inside the housing, so the repair is a complete throttle body, followed by a relearn. A few older designs with a bolt-on sensor are the exception.
Why did P0221 appear right after I cleaned the throttle body?
Spray cleaner can seep into the sensor housing, and the plate position the PCM learned no longer matches a clean bore. Let it dry fully, then run the throttle relearn; if the code stays, cleaner may have damaged the sensor.
Is it the gas pedal sensor?
On most vehicles the pedal has its own sensor codes, such as P2122 or P2138. P0221 normally concerns the second sensor in the throttle body, although a few makes use the same wording for other sensors, so always check the wiring diagram for your model.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy