Code P0566 indicates that the powertrain control module (PCM) has detected a malfunction in the cruise control off signal circuit. This signal is typically sent when the driver presses the brake pedal, clutch pedal (manual transmission), or the cruise control cancel/off switch. The code sets when the PCM sees an unexpected voltage or signal state from this circuit.
The most common cause. A misadjusted or failing brake switch can send a constant 'off' signal, preventing cruise control engagement. This switch often has multiple circuits, and the cruise control portion may fail independently of the brake lights.
On manual transmission vehicles, a defective clutch switch can mimic a constant 'off' signal, disabling cruise control. The switch may stick or fail internally.
Wiring between the brake/clutch switch, cruise control switches, and the PCM can chafe, short to ground, or open, causing an incorrect signal. Common near the pedal area or in the steering column.
The cancel/off switch contacts may wear or become contaminated, sending an intermittent or constant off signal even when not pressed.
Connectors at the brake switch, clutch switch, or cruise control module can develop corrosion or looseness, leading to high resistance and signal errors.
The PCM monitors the off signal circuit. Internal failure is possible but very uncommon. This should only be considered after all other causes are thoroughly ruled out.
Yes, the vehicle is safe to drive. The code only affects cruise control operation; all other systems function normally. However, you should address it to restore cruise control functionality.
Yes, it is the most common cause. The brake light switch often contains separate contacts for the brake lights and the cruise control cancel signal. Even if your brake lights work, the cruise control circuit may be faulty.
Almost never. Many drivers are told the PCM is at fault, but in reality, the issue is almost always a faulty brake switch, clutch switch, or wiring problem. A PCM replacement should only be considered after a thorough professional diagnosis has eliminated all other possibilities.
It is unlikely. P0566 is specific to the cruise control off signal circuit. Low system voltage might cause erratic behavior in many modules, but it would typically set other codes first. Check battery and charging system if multiple unrelated codes are present.