P0642
Sensor Reference Voltage \"A\" Circuit Low
The 5 V reference voltage on the A circuit (used by multiple sensors) is below threshold — short to ground or excessive current draw by a single sensor pulling the rail down.
The 5 V reference voltage on the A circuit (used by multiple sensors) is below threshold — short to ground or excessive current draw by a single sensor pulling the rail down.
Common causes
- high
Sensor or harness shorted to ground
One of the most commonly reported causes for this code — check this first.
Typical part cost: $90-880
- low
ECU reference output damaged
Less common, but worth ruling out after the more likely causes.
Typical part cost: $90-880
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Related codes
See related trouble codes
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Frequently asked questions
What does P0642 mean?
P0642 means "Sensor Reference Voltage \"A\" Circuit Low". It is a generic OBD-II code that points to a fault in the computer & auxiliary output controls.
What are the most common causes of P0642?
sensor or harness shorted to ground; ecu reference output damaged; connector pins corroded - high contact resistance — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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