Damaged, chafed or corroded wiring in the fuel level signal circuit between the engine control unit and the instrument cluster or other receiving module; Poor connection or corroded terminals at the engine control unit, instrument cluster or fuel tank connectors; Faulty fuel level sender or fuel pump module giving an implausible signal to the control unit; Fault in the instrument cluster or receiving module not handling the signal correctly; Communication network fault affecting the transfer of the fuel level data; Internal fault in the engine control unit output stage; Outdated control unit software where the manufacturer has issued an update for this fault.

P0656

Fuel Level Output Circuit.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
56: FaultThe specific fault in that area

What it means

P0656 is the generic SAE J2012 code for a fault in the Fuel Level Output Circuit. The engine control unit sends a fuel level signal to another module, usually the instrument cluster or body control module, and it has detected that this output circuit is not behaving as expected. This is often an electrical fault such as an open circuit, short or wrong voltage, but the exact setting criteria vary by manufacturer and model.

Symptoms

Fuel gauge reads incorrectly, sticks, or drops to empty or full
Low fuel warning light on when the tank has fuel, or not on when it is low
Malfunction indicator lamp on
Fuel gauge needle flickering or moving erratically
Inaccurate range or fuel economy readout on the trip computer

Possible causes

Damaged, chafed or corroded wiring in the fuel level signal circuit between the engine control unit and the instrument cluster or other receiving modulelikely
Poor connection or corroded terminals at the engine control unit, instrument cluster or fuel tank connectorslikely
Faulty fuel level sender or fuel pump module giving an implausible signal to the control unitpossible
Fault in the instrument cluster or receiving module not handling the signal correctlypossible
Communication network fault affecting the transfer of the fuel level datapossible
Internal fault in the engine control unit output stagerare
Outdated control unit software where the manufacturer has issued an update for this faultrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any related codes for the fuel level sensor, network communication or instrument cluster
Compare the fuel gauge reading with the actual fuel level in the tank and see whether the fault is constant or intermittent
Visually inspect the wiring and connectors for the fuel level circuit, including under the rear seat or boot floor and near the tank, for damage, water ingress or corrosion
Check live data for the fuel level input and output values and see whether they agree and respond sensibly as the level changes
Check the fuel level sender signal and its resistance against the manufacturer specification, as the values depend on the model
Use the wiring diagram to test the output circuit for continuity, short to earth, short to supply and correct voltage
Check the power and earth supplies to the engine control unit and instrument cluster
Check for manufacturer service bulletins or software updates relevant to the vehicle

How to fix

Repair or replace damaged wiring and clean or replace corroded or loose connectors
Replace the fuel level sender or fuel pump module if its signal is faulty
Repair any network communication fault found
Repair or replace the instrument cluster or receiving module if it is confirmed faulty
Replace the engine control unit only after all wiring and supply faults are ruled out and the unit is confirmed faulty
Update the control unit software if an update exists for this fault, then clear the codes and confirm the fault does not return

Can I keep driving?

Low severity

The car is usually safe to drive as this is mainly a signalling fault, but the fuel gauge may be unreliable so keep track of fuel by mileage and refuel regularly to avoid running dry. Book it in soon, as the warning lamp may mask other faults at an MOT or emissions check.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.