P0266 - monitored circuit or component (Sensor Correlation)
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Cylinder 2 Contribution/Balance (P0266). Two sensors that should track together deviate beyond tolerance, forcing a fail-safe for safety. The fault is isolated to cylinder 2, positioned on the inner block section with asymmetric intake runner pulses. This directly impacts individual cylinder volumetric efficiency, firing synchronization, and dedicated harness branch loading.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Cylinder 2 Contribution/Balance – Signal Voltage | Voltage (V) | 0.50 - 4.50 V (tracks operating range) | Ignition ON, connector engaged |
| 5 V Reference Voltage | Voltage (V) | 4.95 - 5.05 V | Ignition ON at sensor connector |
| Sensor Ground Voltage Drop | Voltage (V) | < 0.05 V (< 50 mV) | Under load to chassis ground |
| Signal Wire Continuity | Resistance (Ω) | < 0.5 Ω (Open = OL) | Disconnected harness between sensor and ECM |
Ignition ON, connector engaged
Ignition ON at sensor connector
Under load to chassis ground
Disconnected harness between sensor and ECM
Oscilloscope Waveform Analysis
100 ms/div, 1 V/divPossible Causes
Mid-block harness fatigue (cylinder 2): Wiring friction against valve cover bracket and hydraulic standing pressure waves in fuel rail between cylinder 1 and 2.
Asymmetric intake tumble:Tumble airflow disruption and localized carbon deposits on intake valves of cylinder 2.
Chafed or pinched wiring harness along the signal path to Cylinder 2 Contribution/Balance
Poor ground connection or excessive voltage drop (> 0.1 V) at the ground point for Cylinder 2 Contribution/Balance
Defective internal output driver or reference circuit in the control module for Cylinder 2 Contribution/Balance
Symptoms
Recommended Solution
Swap component on cylinder 2 over to cylinder 3 and clear DTCs to confirm if fault follows.
Smoke test intake manifold runner gasket at cylinder 2 to rule out unmetered false air and pressure standing waves.
Graph both paired sensors simultaneously in scan-tool live data to pinpoint which sensor is diverging.
Verify loaded supply voltage and harness terminal pins at Cylinder 2 Contribution/Balance.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Cylinder 2 Contribution/Balance.
Unplug the sensor:the signal must swing to a known rail. Replace the sensor or repair the wiring based on the result.
Mechanic's Tip
Pro-tip for cylinder 2: Intake manifold runner geometry exposes cylinders 2 and 3 to distinct pressure pulsation waves. Smoke test the intake runner seals thoroughly.