P0641 to P0643, P0651 to P0653, P0697 to P0699 and P0657 to P0659: sensor reference and actuator supply

What does P0641 mean?

The engine computer feeds several sensors from shared, carefully regulated supplies, usually grouped into circuits A, B and C, and reads their signals against that reference. If one reference is pulled low by a short in any sensor or wire on it, every sensor on that circuit reads wrong at the same moment. That is why these codes usually arrive with a crowd of others, for the throttle, the pedal, the pressure sensors, and why the car may go into a protective mode with very little power.

What causes P0641?

1. A short to ground in one sensor or its wire on the shared circuit
2. A sensor with water inside it pulling the reference down
3. A chafed harness where it touches the engine or a bracket
4. A fault inside the engine computer, which is the least likely cause

What to check first for P0641

• Write down every code stored: they show which sensors share the failing circuit
• Unplug the sensors on that circuit one at a time and see whether the reference voltage recovers
• Inspect the harness for chafing, especially near the engine and the exhaust
• Look for water in sensor connectors after rain or washing the engine

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