P0398
Cylinder 1 Pressure Sensor Circuit High
Combustion / cylinder pressure sensor
Generic OBD-II
High
What it means
P0398 means the cylinder 1 combustion pressure sensor circuit is reading too high. On engines fitted with in-cylinder pressure sensors, this signal helps the ECM monitor and fine-tune combustion. A circuit fault is usually the sensor or its wiring, and while the car often still drives, the engine loses that feedback until it is repaired.
High
Can I keep driving? Usually still drivable — this is a sensor-circuit fault — but the engine may lose the combustion feedback it uses to fine-tune running, so power or smoothness can suffer.
Common symptoms
What you'll notice
- Check-engine light on
- Often no obvious change in how the car drives
- Possible reduced power or a limp-mode restriction
- Slightly rougher running on affected engines
Common causes
Most likely first
- Failed cylinder 1 pressure sensorLikely
- Open or shorted wiring in the sensor circuitCommon
- Poor or corroded connection at the sensorCommon
- Loss of reference voltage or ground to the sensorLess often
- ECM fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the fault is on the cylinder 1 sensor.
- Inspect the sensor connector and wiring for damage or corrosion.
- Check the circuit for a short to voltage and confirm reference/ground.
- Compare the sensor's signal against spec with a scan tool if available.
- Replace the cylinder 1 pressure sensor if it tests faulty; clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0398?+
Short-term, usually yes, since it is a sensor-circuit fault. Some engines may reduce power to protect themselves, so have it checked before long trips.
Can I just clear P0398?+
It returns once the ECM rechecks the circuit. The sensor or wiring must be repaired first.
Related codes
Often seen with P0398
Read & clear P0398 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX