Cylinder 1 Pressure Sensor Circuit Intermittent/Erratic

Where it lives

For P0399, the sensor sits on the circuit this code reports. The description of P0399 puts it on cylinder 1.

Check these first

• A loose connector at the cylinder 1 pressure sensor
• A harness that loses the sensor 1 signal with vibration
• A sensor 1 failing as it heats up
• Corroded sensor 1 pins
• Oil or debris moving on the sensor 1 tip

What to do next

1. Wiggle test the sensor 1 harness with a scan tool connected
2. Inspect the cylinder 1 connector for loose or pushed pins
3. Watch cylinder 1 pressure as the engine warms up
4. Clean the sensor 1 tip
5. Replace the cylinder 1 pressure sensor if the signal jumps
6. Clear the code and retest

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