Code Definition

P0642 — Sensor power supply circuit low - Circuit A

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0642

P0642 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0642 is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0642 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The fault code P0642 is set when the Engine Control Module (ECM) detects a lower than expected voltage level in the sensor reference voltage circuit 'A.' This reference circuit typically provides a 5-volt signal to various sensors. When the voltage in this circuit falls below a specific threshold, it indicates a problem such as a short to ground or excessive resistance in the circuit. This lower voltage can lead to incorrect sensor readings and impaired engine performance. The code is triggered because the ECM monitors the reference voltage to ensure it remains within a specified range for pro...

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