P0643
Sensor Reference Voltage "A" Circuit High
- Severity
- High
- Driving
- Drive only to a garage
Sensor reference voltage "A" is reading high - the regulated supply to a group of sensors is above where it should be, usually because the circuit has been shorted to a higher voltage or has lost its earth. Sensors on that reference will report values that are too high across the board.
Possible causes
- CommonReference circuit shorted to battery voltage or to another supply
- CommonChafed harness bridging the reference to a supply wire
- CommonWater or corrosion in a connector bridging adjacent pins
- PossibleDamage from previous work - a probe pushed into the wrong pin, or a jump start error
- PossibleFailed control module reference supply
What you might notice
- Many sensor codes at once, most reading high
- Limp mode or reduced power
- Engine running badly
- Check engine light on
What to check, in order
- Fix the reference before diagnosing any sensor stored alongside it.
- Look for a short to a supply wire. A reference sitting above its regulated value has to be getting voltage from somewhere.
- Inspect connectors for corrosion bridging adjacent pins.
- Check the harness for chafe damage where the reference runs alongside supply wires.
- Ask what work was done recently. Back-probing the wrong pin or a jump start with reversed leads can damage a reference circuit permanently.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Computer output circuits and control module
P0600P0601P0602P0603P0604P0605P0606P0607P0608P0609P0610P0611P0612P0613P0614P0615P0616P0617P0618P0619P0620P0621P0622P0623P0624P0625P0626P0627P0628P0629P0630P0631P0632P0633P0634P0635P0636P0637P0638P0639P0640P0641P0642P0643P0644P0645P0646P0647P0648P0649P0650P0651P0652P0653P0654P0655P0656P0657P0658P0659P0660P0661P0662P0663P0664P0665P0666P0667P0668P0669P0670P0671P0672P0673P0674P0675P0676P0677P0678P0679P0680P0681P0682P0683P0684P0685P0686P0687P0688P0689P0690P0691P0692P0693P0694P0695P0696P0697P0698P0699