What it means
Cylinder-to-cylinder pressure variation on cylinder 1 is below the calibrated minimum — pressure stays unusually constant cycle-to-cycle, often a sign that the closed-loop combustion controller has lost authority or the sensor signal is filtered.
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 records how combustion pressure changes through successive engine cycles, and the control module uses those changes to assess combustion control. This code sets when cylinder 1's pressure variation is below the calibrated minimum, meaning its signal is unusually flat or the controller cannot detect the expected changes.
Common causes
Most likely first.
- Faulty cylinder 1 pressure sensor
- Restricted or filtered sensor signal
- Combustion control fault
- Wiring or connector fault
Symptoms
- Check engine light on
- Rough running or misfire
- Reduced power
- Uneven engine response
How to diagnose it
- Use a scan tool to save freeze-frame data and compare cylinder 1's pressure trace or variation reading with other cylinders.
- Check live data while engine conditions change to see whether the cylinder 1 signal responds, or stays unusually constant.
- Inspect the cylinder 1 pressure sensor connector and harness for corrosion, loose pins, damage, or a connection that could distort the signal.
- Check the sensor signal circuit for restrictions, poor connections, or filtering caused by wiring or an intervening component.
- If the circuit is sound, compare the sensor response and combustion-control operation with the manufacturer's specification.
Common fixes
- Clean and secure the cylinder 1 pressure-sensor connector.
- Repair damaged cylinder 1 signal wiring or poor terminal contact.
- Correct a confirmed restriction or filtering issue in the pressure-sensor signal path.
- Replace the cylinder 1 pressure sensor if it fails the manufacturer's response checks.
- Repair a confirmed combustion-control fault affecting cylinder 1.
Can I keep driving?
If the engine runs smoothly, drive gently and arrange diagnosis soon; avoid heavy loads if power is reduced. A pressure signal that does not track combustion changes can impair cylinder 1 control and contribute to rough running or misfire.
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.