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P codepowertrainMedium severity

P0699Sensor Reference Voltage "C" Circuit High

The 5-volt sensor reference "C" circuit is reading higher than expected, typically from a short to battery or ignition voltage in the shared sensor supply.

Definition

The PCM continuously checks its 5-volt reference buses against tolerance windows, and P0699 sets when the reference "C" bus rises above its high threshold — almost always a short to battery or ignition voltage somewhere in the shared harness or a connector. Overvoltage on the bus skews every sensor fed by it high, so companion high-signal sensor codes are common, and sustained overvoltage can damage the sensors themselves. The MIL illuminates and reduced-power strategies may engage.

Common causes

  • Reference wire chafed against a battery or ignition voltage feed
  • Water intrusion bridging power into a shared connector
  • Damaged sensor internally leaking supply voltage onto the reference terminal
  • Incorrectly repaired harness or aftermarket wiring spliced into the bus
  • PCM internal regulator fault

Common misdiagnoses

  • Replacing sensors that set companion high-signal codes
  • PCM replaced before checking the harness for a short to voltage
  • Charging system diagnosed for the elevated sensor readings

Troubleshooting steps

  1. 1.Note all companion high-signal codes

    Sensors reading pegged-high at the same time identify the components sharing reference C.

  2. 2.Measure the bus voltage key-on and engine running

    Backprobe the reference terminal; anything meaningfully above 5.1 volts — especially near 12 volts — confirms a short to power.

  3. 3.Check whether the fault follows ignition state

    Voltage present only with the key on suggests an ignition-fed short; voltage at all times points to a constant battery feed contact.

  4. 4.Isolate branches of the bus

    Unplug shared sensors and connectors one at a time; if the overvoltage disappears, inspect that branch for chafe or water.

  5. 5.Verify the PCM output unloaded

    With the harness disconnected at the PCM, the reference pin should read 4.9–5.1 volts on its own before the module is condemned.

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