What does it mean?
In the pressure sensing circuit for cylinder 2 the module provides the supply and the return path, and it expects the signal voltage to remain inside a narrow window whatever the engine is doing. This code is stored when the signal stays above the calibrated maximum for longer than the monitor allows, a level that a correctly connected sensor cannot produce. The most common mechanism is a lost return path, because without a solid low reference the signal line simply rises toward reference voltage. The alternative explanations are contact with a higher voltage circuit or an internal break in the sensor that leaves the module input floating. With the reading out of range the module stops using cylinder 2 combustion feedback, applies default fueling and turns on the MIL (check engine lamp).
Symptoms
- MIL (check engine lamp) on with a fault recorded against the cylinder 2 pressure sensor
- Idle noticeably rougher and the engine sounding harder than usual
- Difficult cold starting and heavier smoke on the first start of the day
- Reduced power because combustion feedback from that cylinder is ignored
- Increased fuel consumption and, on some applications, limp mode
- Uneven pull that the driver feels most clearly under light acceleration
Likely causes
- Low reference circuit open or high in resistance, letting the signal float to the top of its range
- Signal wire shorted to the five volt reference or to battery voltage inside a damaged harness section
- Broken signal conductor so that only the internal pull up of the module is measured
- Internally open sensing element or a fractured internal joint in the sensor body
- Corroded terminals adding series resistance that pushes the reading upward
- Moisture or salt in the connector creating a leakage path from a powered pin to the signal pin
- Module input fault, considered last and only after the reference and ground circuits have been verified
How to fix it
- Read the freeze frame and check for pressure sensor codes on other cylinders that would move the diagnosis to a shared circuit
- Inspect the connector for corrosion, moisture, a damaged seal and pushed back terminals, and check the harness where it passes over hot components
- With the ignition on and the sensor connected, backprobe the signal line and confirm the value is genuinely at the top of its range
- Unplug the sensor and measure the low reference to ground on the harness side, since high resistance here is the most frequent cause
- Verify continuity of the signal wire back to the module and confirm it is not shorted to the reference or to a powered circuit
- Substitute a known good sensor of the same specification if one is available and see whether the fault follows the sensor
- Carry out the repair, clear the memory and confirm on a full warm up and road test that the cylinder 2 signal now stays inside its normal window