What does it mean?
OBD II fault code is defined as “Throttle/Pedal Position Sensor/Switch C Circuit Malfunction”, 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 P0225 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.
Note: “Circuit Malfunction” indicates that there is a malfunction in the control circuit, as opposed to a fault in a sensor or other component. With “Circuit Malfunction” codes, replacement of sensors and components in the affected circuit will almost never resolve the problem, since as the code suggests, the trouble is in the circuit .
This distinction between “circuit” and “sensor/component” is a great help to anyone trying to diagnose a circuit malfunction code, since it narrows the list of possible causes down considerably.
The causes of “Circuit Malfunction” codes are much the same as those for “Open Circuits” i.e., broken wiring, poor connections across electrical connectors or previously repaired wiring, loss of ground that prevents current flow, blown fuses, defective relays, faulty switches, or any of a host of other issues and problems that prevents a flow of current through wiring. Issues like high/low/intermittent voltages can set a “Circuit Malfunction” code on some applications.
Moreover, “Circuit Malfunction” codes could also indicate a problem with negative current control / flow, as well as issues with failed or failing PCM’s (Powertrain Control Modules), although control module failure is a rare event.