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P218BFuel Level Sensor "B" Stuck

The secondary fuel level sensor, used in saddle-style tanks with two senders, is not changing its reading the way fuel consumption or refueling says it should.

Definition

Vehicles with saddle-shaped fuel tanks use two level senders, and the module averages them while a jet (transfer) pump siphons fuel from the secondary side to the primary side. P218B sets when the "B" sender's reading stays fixed despite fuel being burned or added, failing the PCM's rationality check. Symptoms include an inaccurate or erratic fuel gauge and, because fuel level gates EVAP leak testing, incomplete EVAP monitors; a failed transfer jet pump can also strand fuel on the secondary side and mimic or accompany this fault.

Common causes

  • Secondary sender float arm stuck or binding
  • Worn or sulfur-contaminated resistor card on the B sender
  • Failed jet/transfer pump leaving the secondary side level unchanged
  • High resistance or open in the B sender wiring
  • Damaged float or obstructed float travel in the saddle section

Common misdiagnoses

  • Entire fuel pump module replaced when only the B sender card is worn
  • Primary (A) sender replaced instead of the secondary unit
  • Instrument cluster replaced for a tank-side fault
  • EVAP system parts replaced chasing monitor readiness

Troubleshooting steps

  1. 1.Read both fuel level PIDs separately

    Compare sensor A and sensor B values through a refuel; only B remaining fixed isolates the secondary side.

  2. 2.Rule out a transfer pump failure

    If B legitimately stays full while A drops fast, the jet pump siphon may be clogged; verify whether the secondary side is actually transferring fuel.

  3. 3.Measure B sender resistance

    At the secondary tank connector, confirm a smooth resistance sweep across float travel; a fixed or open reading condemns the sender.

  4. 4.Check wiring to the secondary sender

    Inspect the tank-top connector and inter-tank harness for corrosion, chafing, and excessive voltage drop.

  5. 5.Service the secondary sending unit

    Drop or access the tank, inspect the float arm and wiper card, and replace the sender or module half as needed, then verify PID movement.

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