P0272 - monitored circuit or component (Circuit Low)
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Cylinder 4 Contribution/Balance (P0272). The signal is below the lower threshold, typically from a short to ground or an internally shorted sensor. The fault is isolated to cylinder 4, positioned at the flywheel end (exposed to torsional vibration harmonics). 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 4 Contribution/Balance – Signal Voltage | Voltage (V) | < 0.20 V (fault state) | 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
Short to ground on the signal wire or an internal short circuit within Cylinder 4 Contribution/Balance
Flywheel end torsional vibration (cylinder 4): High cyclic vibration harmonics from dual-mass flywheel and transmission input shaft transferred to terminal pins.
Rear cylinder coolant stagnation:Thermal stratification at cylinder head rear bulkhead and harness chaffing against bellhousing casting.
Chafed or pinched wiring harness along the signal path to Cylinder 4 Contribution/Balance
Poor ground connection or excessive voltage drop (> 0.1 V) at the ground point for Cylinder 4 Contribution/Balance
Defective internal output driver or reference circuit in the control module for Cylinder 4 Contribution/Balance
Symptoms
5
Recommended Solution
Swap component on cylinder 4 over to cylinder 1 and clear DTCs to confirm if fault follows.
Inspect wiring harness brackets against transmission bellhousing casting and rear engine mount for vibration chafing.
Measure signal wire resistance to chassis ground with connector unplugged (must exceed 10 kΩ; low reading confirms short to ground).
Verify loaded supply voltage and harness terminal pins at Cylinder 4 Contribution/Balance.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Cylinder 4 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 4: Cylinder 4 sits closest to the flywheel and absorbs powertrain torsional harmonics. Inspect wiring closely for chafing against bellhousing brackets.