Engine computer
P0641
Sensor Reference Voltage "A" Circuit/Open
The engine computer has found a problem with its own memory, processor, programming or a reference voltage it supplies to sensors. A shorted sensor on the shared 5-volt supply is the usual cause. Unplugging sensors one at a time finds it.
Fix it soon
Can I keep driving? For a short while, gently. Have it checked in the next few days, and stop if the car feels, sounds or smells different. The car may run normally or behave oddly. It needs proper diagnosis before any parts are bought.
Common causes
- Low battery voltage or a poor ground (check this first)
- Water or corrosion in a connector
- A shorted sensor pulling down a shared reference voltage
- Software that needs updating
- A failed control module (less common than the others)
Listed roughly from most to least likely. The same code can have different causes on different cars.
What to do
- Have the battery, charging system and grounds tested.
- Ask the dealer whether there's a software update or a service bulletin for this code.
- Have a shop test before replacing the computer. It's often not the computer.
General guidance. Your owner's manual wins. If a red warning light is on or the car drives differently, stop safely and get help.
Related codes
- P0600Serial Communication Link
- P0601Internal Control Module Memory Check Sum Error
- P0602Control Module Programming Error
- P0603Internal Control Module Keep Alive Memory (KAM) Error
- P0604Internal Control Module Random Access Memory (RAM) Error
- P0605Internal Control Module Read Only Memory (ROM) Error
- P0606Control Module Processor
- P0650Malfunction Indicator Lamp (MIL) Control Circuit
Track this automatically in Tagwell Auto
Tagwell Auto keeps your car's service dates and mileage, so when a code shows up you know what was done last. With a Bluetooth reader for the car's diagnostic port (called OBD-II), the phone app can read the code itself.