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P0656Fuel Level Output Circuit

The circuit carrying the fuel level signal between modules has an electrical fault, so the PCM is not receiving or sending a valid fuel level value.

Definition

The PCM uses fuel level data — often relayed from the instrument cluster or body module, or output to them — for EVAP leak monitoring and gauge operation, and it monitors the fuel level output circuit for opens and shorts. P0656 sets when that circuit reads out of range or the signal is missing. Symptoms include an erratic, empty, or full-pegged fuel gauge, and the PCM will typically suspend EVAP monitors because leak tests require a known fuel level, which can leave inspection readiness monitors incomplete. The engine runs normally.

Common causes

  • Open or shorted wiring between the fuel tank sender, cluster/body module, and PCM
  • Worn or contaminated fuel level sender resistor card in the tank
  • Corroded connector at the fuel pump module (common after tank service or in rust-belt vehicles)
  • Faulty instrument cluster or body control module relaying the level signal
  • Failed input/output circuit in the PCM

Common misdiagnoses

  • Entire fuel pump assembly replaced when only the sender circuit wiring or connector is faulty
  • Fuel gauge or cluster replaced without testing the sender resistance range
  • EVAP components (purge/vent valves) replaced because EVAP monitors would not run
  • PCM replaced before checking the tank harness connector

Troubleshooting steps

  1. 1.Compare gauge, scan data, and actual fuel

    View the fuel level PID on a scan tool in both the PCM and cluster/BCM and compare it against the known tank contents to determine where the signal is lost.

  2. 2.Test the sender's resistance sweep

    At the tank connector, measure sender resistance (spec varies, e.g. roughly 40-250 ohms across the range) and confirm it changes smoothly; dead spots indicate a worn resistor card.

  3. 3.Inspect the tank harness connector

    Check the fuel pump module connector for green corrosion, spread terminals, or damage, especially if the tank or pump was recently serviced.

  4. 4.Verify the circuit between modules

    Test continuity and shorts on the level signal wire from the sender to the receiving module and on the output circuit toward the PCM per the wiring diagram.

  5. 5.Confirm the repair restores EVAP readiness

    After repair, verify the fuel level PID tracks correctly and that EVAP monitors will run to completion, since a plausible level between about 15% and 85% is required for most leak tests.

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