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P codepowertrainMedium severity

P0697Sensor Reference Voltage "C" Circuit/Open

The 5-volt reference "C" supply that the engine computer sends to a group of sensors is out of range or open.

Definition

The PCM generates several independently regulated 5-volt reference buses, and reference "C" powers a specific group of sensors that varies by manufacturer (commonly pressure sensors, position sensors, or pedal circuits). P0697 sets when that bus voltage falls outside tolerance or the circuit is open. Because multiple sensors share the bus, several implausible-signal sensor codes usually set at the same time, and reduced-power or limp mode plus an illuminated MIL are common results.

Common causes

  • A sensor on the reference C bus internally shorted, dragging the supply down
  • Harness chafe shorting the reference wire to ground or to voltage
  • Water intrusion or corrosion at a connector shared by the bus
  • Damaged terminal or broken reference wire creating an open
  • PCM internal 5-volt regulator fault

Common misdiagnoses

  • Individually replacing the sensors that set companion codes when the shared supply is at fault
  • PCM replaced when one shorted sensor is pulling the bus down
  • Accelerator pedal or throttle body replaced for the limp-mode symptom

Troubleshooting steps

  1. 1.List all companion codes

    The sensors that set simultaneous codes identify which components share reference C on this vehicle — confirm with the wiring diagram.

  2. 2.Measure the reference voltage at an accessible sensor

    Backprobe the 5-volt terminal; a healthy bus reads 4.9–5.1 volts with the key on.

  3. 3.Unplug shared sensors one at a time

    Watch the reference voltage while disconnecting each sensor on the bus — recovery to 5 volts identifies the internally shorted sensor.

  4. 4.Inspect the shared harness

    If no sensor restores the bus, check the reference wiring for chafe points, pinched sections, and water-filled connectors.

  5. 5.Test at the PCM connector last

    With the harness disconnected, a reference output that is still wrong at the PCM pin (after verifying powers and grounds) indicates an internal regulator fault.

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