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P0397 — Cylinder 1 Pressure Sensor Circuit Low

Generic OBD-II · all makesPowertrain (engine & transmission)

The P0397 code indicates that the engine control module has detected a voltage signal from the Cylinder 1 pressure sensor that is lower than the expected operating range. This typically suggests an electrical open or a short to ground in the sensor circuit.

Symptoms

What causes it — most likely first

1. Failed Pressure Sensor

Internal failure of the Cylinder 1 pressure sensor causing it to output a voltage below the minimum threshold.

2. Wiring Short to Ground

The signal wire is pinched or worn, allowing the voltage to leak to the engine block or chassis.

3. Corroded Connector

Moisture or contaminants in the sensor connector causing high resistance or a poor electrical connection.

4. Open Circuit

A broken wire or disconnected pin in the harness between the sensor and the control module.

5. Control Module Failure

Internal failure of the PCM/ECM processing the sensor input, though this is very rare.

How it's diagnosed

  1. Confirm the code and check for any other cylinder-specific pressure sensor codes.
  2. Inspect the wiring harness and connector for visible damage, fraying, or corrosion.
  3. Use a digital multimeter to verify the reference voltage reaching the sensor.
  4. Test the sensor output signal during the combustion cycle using an oscilloscope.
  5. Perform a continuity and load test on the signal wire from the sensor to the ECM.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0390 — Camshaft Position Sensor B Circuit BanP0391 — Camshaft Position Sensor B Circuit RanP0392 — Camshaft Position Sensor B Circuit LowP0393 — Camshaft Position Sensor B Circuit HigP0394 — Camshaft Position Sensor B Circuit IntP0395 — Cylinder 1 Pressure Sensor Circuit

Frequently asked

Can a mechanical engine failure trigger P0397?

No, this code refers specifically to the electrical circuit of the sensor, not the actual pressure levels within the cylinder.

Is it common to replace the PCM for this code?

No. It is very rare for the PCM to be the cause; the issue is almost always the sensor itself or the associated wiring.

Will the vehicle still be drivable with this code?

Yes, but the engine may operate in a default map, leading to decreased fuel efficiency and power.