What does it mean?
The pressure signal from cylinder 3 has to be continuous and follow the piston smoothly through every stroke, with no gaps or steps between samples. This code is stored when that signal briefly disappears, jumps to a value combustion cannot create, or turns noisy and then returns to normal behaviour. Because the disturbance comes and goes, the circuit is not permanently broken; a connection or the sensor itself is unstable under vibration, heat or load. Every interruption costs the module its combustion feedback for that cylinder for a moment, which the driver often perceives as a short change in how the engine runs. This kind of fault can set on one journey and stay quiet on the next, so the diagnosis must aim at reproducing the condition rather than guessing at a component.
Symptoms
- MIL (check engine lamp) on, often only after the disturbance has occurred on several journeys
- Momentary roughness or a brief stumble that clears without any driver input
- Idle that turns uneven for a few seconds and then settles again
- Random small hesitations under acceleration with no repeatable pattern
- Combustion noise on diesel applications that changes from time to time
- Occasional short lived power reduction that disappears after a restart
Likely causes
- Sensor connector not fully latched or a terminal that has lost its spring tension
- Wire in the cylinder 3 branch chafed against the head or a bracket and touching only when the engine rocks on its mounts
- Oil or moisture entering the connector and forming an unstable leakage path
- Sensing element breaking down internally and producing noise as it warms up
- High resistance in the shared five volt reference or low reference, disturbing the signal under load
- Harness rerouted or clipped incorrectly after previous work, allowing interference from injector or glow plug switching
- Loose sensor or a failing seal letting the element shift slightly in its bore
How to fix it
- Read the freeze frame and note the coolant temperature, engine speed and load at which the events cluster
- Inspect the connector for a broken lock, loose terminals, oil contamination and a hardened seal, then check the harness for rub points along the head
- Record the sensor signal on a scope or graphing meter while wiggle testing the sensor, the harness branch and the module connector
- Monitor the five volt reference and the low reference during the same test, since an unstable reference upsets several sensors at once
- Take a live data recording on a road test that reproduces the freeze frame conditions and look for dropouts that coincide with bumps or throttle changes
- Repair the loose or damaged connection, or renew the sensor once it is proven to be the source, refitting with a new seal at the specified torque
- Clear the memory and confirm over several heat cycles and a mixed drive that the signal remains stable