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Throttle/Petal Position Sensor/Switch B Circuit Malfunction

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Severity

Medium

Can I keep driving?

Usually drivable, but get it diagnosed without delay.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Scan the car and note the freeze-frame data, engine speed, throttle angle and the conditions when it logged. That tells you whether it's a steady fault or an intermittent dropout. 2. Get on the wiring and connectors at the throttle body before you condemn any parts.

  • PPowertrain
  • 0Generic code
  • 2Fuel / Air
  • 21Sequence number

What does it mean?

OBD II fault code is defined as “Throttle/Pedal Position Sensor/Switch B Range/Performance”, and set when the PCM (Powertrain Control Module) detects a signal voltage from the TPS (Throttle Position Sensor) that does not correlate with the current engine speed. On most applications, a voltage or resistance deviation of more than 10% of the specified reference value will cause a code to be stored and the CHECK ENGINE light to be illuminated.

As a rule, the PCM will recognize a closed throttle as a zero, or close to a zero voltage/resistance value, but be sure to check the actual voltage/resistance for a closed throttle against values stated in the manual. Essentially, the TPS is a type of variable resistor that is attached to the throttle body, and it alters the throttle opening as the circuit resistance/voltage changes due to movements of the accelerator pedal.

The TPS relies on signals from the PCM (derived from the pedal) to actuate the throttle, on the one hand, while at the same time, supplying the PCM with precise information on how wide the throttle is open at any given time. To complete the circuit, there is another sensor attached to the accelerator. This is most commonly a Hall Effect sensor that generates a current when a moving part is moved through a magnetic field.

This signal is used by the PCM to actuate a mechanism (which can be a motor, solenoid, or other device) in the TPS to change the position of the throttle plate. Changes in the throttle opening serve to alert the PCM to make suitable adjustments to the ignition timing, VVT/VCS timing, and injector pulse width/duration to ensure peak engine performance under any given load.

NOTE: Code P0221 is only relevant to “drive-by-wire” systems in which there are no physical connections, such as throttle cables, between the accelerator pedal and the throttle plate/body. In some applications, there may be additional sensors and devices fitted to act as back-ups should a primary component or sensor fail. The image below shows a typical Throttle Position Sensor and its location.

Symptoms

Likely causes

How to fix it

Codes From the Same System

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.