What it means
Cylinder 1 pressure sensor above upper plausibility — open signal or short to B+. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 1 pressure sensor measures combustion pressure in that cylinder, and the engine control module uses its signal to monitor combustion. This code sets when the signal is higher than the module considers plausible, which can happen if the signal wire is open or shorted to battery voltage.
Common causes
Most likely first.
- Open signal line
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Rough running or misfire
- Reduced engine power
- Hard starting
How to diagnose it
- Use a scan tool to record freeze-frame data and check whether the cylinder 1 pressure reading is high whenever the fault is active.
- Inspect the cylinder 1 sensor connector for moisture, corrosion, damaged seals, or pins pushed out of position.
- Check the sensor harness for chafing, pinching, or contact with a battery-positive wire, especially near bends and hot or moving parts.
- With the wiring diagram, check the cylinder 1 signal, supply, and ground circuits for opens or shorts to battery voltage.
- If the wiring checks out, compare the sensor output and combustion-pressure data with the manufacturer's specification to assess the sensor.
Common fixes
- Clean and securely reconnect the cylinder 1 sensor connector if its contacts are sound.
- Repair an open signal wire or damaged connector pin.
- Repair harness insulation or routing where the signal wire contacts a battery-positive source.
- Replace the cylinder 1 pressure sensor if its output fails the manufacturer's checks.
Can I keep driving?
Avoid hard acceleration and long trips while the engine runs roughly or loses power. A false pressure signal can disrupt combustion control and lead to misfires or stalling.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.