P0272 - monitored circuit or component (Circuit Low)
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the monitored circuit or component (P0272). The signal is below the lower threshold, typically from a short to ground or an internally shorted sensor.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Affected sensor/actuator, wiring and control module (ECM) – 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
Signal wire shorted to ground, or an internally shorted sensor
Chafed, pinched or heat-damaged harness along the signal path
Poor sensor ground or a corroded ground point (voltage drop > 0.1 V)
Failed driver or reference output inside the control module (verify last, after wiring)
Symptoms
Recommended Solution
Read freeze-frame data and note the RPM/load at which the code sets.
Back-probe signal, 5 V reference and ground at the sensor with ignition ON.
Wiggle the harness and connector while watching the signal — a jump confirms an intermittent.
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
Always run a loaded voltage-drop test on the sensor ground with ignition ON. A drop above 0.1 V shifts the whole signal and tricks the module into setting sensor codes on a good sensor.