Staff Answer
Oct 27, 2026 - 03:54 PM
Diagnostic Trouble Code (DTC) P2403 stands for "Evaporative Emission System Leak Detection Pump Sense Circuit Low". This code is triggered when the Engine Control Module (ECM) or Powertrain Control Module (PCM) detects that the electrical signal voltage returned from the EVAP Leak Detection Pump (LDP) internal sense/reed switch stays below the expected minimum manufacturer threshold (typically indicating a short to ground or an open circuit condition).
The Leak Detection Pump (LDP) pressurizes or pulls a vacuum on the EVAP system during self-test routines to check for fuel vapor leaks. The "sense circuit" relays the physical movement of the internal pump diaphragm/reed switch back to the PCM. When this signal remains stuck low during activation tests, DTC P2403 is set.
Common Symptoms of DTC P2403
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Illuminated Check Engine Light (CEL): The PCM immediately turns on the Malfunction Indicator Lamp (MIL).
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Failed State Emissions / Smog Test: The vehicle will fail readiness tests due to incomplete or faulted EVAP monitoring.
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Slight Fuel Odor: Minor gasoline odor near the rear wheel well or fuel tank area if an EVAP leak accompanies the circuit fault.
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No Noticeable Drivability Issues: The vehicle typically drives normally without engine misfires or stalling, as EVAP circuits do not alter primary engine timing or fueling.
Primary Root Causes of DTC P2403
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Short to Ground in Sense Wiring Harness: Damaged, chafed, or pinched wires shorting the LDP sense signal line directly to chassis ground.
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Defective EVAP Leak Detection Pump (LDP): Internal failure, stuck-open reed switch, or burnt internal contact points inside the LDP assembly.
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Corroded or Damaged Electrical Connector: Water intrusion, bent pins, or fuel vapor contamination inside the LDP harness connector plug.
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Open Sense Circuit / Blown Fuse: Broken signal wire or loss of power feed to the leak detection pump assembly.
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Faulty PCM / ECM: Rare internal module circuit failure or corrupted engine management software.
Watch the video below for a step-by-step visual guide on testing EVAP leak detection pump circuits and fixing P2403:
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