P2403

P2403 means the ECM is seeing an open circuit on the LDP pressure-sense feedback line — the sensor that reports tank/system pressure back to the ECM during the leak test is either disconnected, has a broken signal wire, or the sensor element itself is open internally. The LDP sense circuit is a 0-5V analog signal that scales linearly across roughly -10 to +10 inH2O of EVAP system pressure (most platforms idle around 2.5V at atmospheric); a clean open reads as 5.0V (pulled up) or 0.0V (floating) depending on the ECM's bias scheme, and that's the signature the code is flagging. Cheapest-first ladder: locate the LDP sense connector (typically a 3-pin: 5V reference, signal, ground), back-probe the 5V reference pin and confirm 4.95-5.05V at KOEO (no voltage = ECM reference fault or short downstream), back-probe the signal pin and confirm a stable 2.3-2.7V at atmosphere with the system vented, then key-off and watch the signal climb during a commanded pump cycle (a working sensor sweeps to roughly 3.5-4.0V at +5 inH2O of test pressure). If reference and ground are good but signal is stuck at rail, the sensor element is open. Expensive misdiagnosis caveat: VW/Audi/Chrysler LDP is mounted in a notorious water-collection point above the rear axle — corrosion at the connector is the #1 root cause; replace the pigtail before replacing the pump, and verify the sense and control connectors are not cross-swapped after a previous repair (an easy mistake on combined assemblies).

Vehicle-specific patterns: 1998-2009 VW/Audi (Jetta, Passat, Golf, A4, A6) throws P2403 from a broken sense-wire pin inside the rear-axle LDP connector — the pin backs out of the housing during a harness disturbance and the ECM sees it as open. 1998-2008 Chrysler/Jeep/Dodge (Sebring, Wrangler, Grand Cherokee) combined NVLD/LDP units throw P2403 when the internal pressure-switch contacts oxidize and fail open. 1996-2005 Mercedes-Benz (W202, W203, W211) throws P2403 from a cracked sensor housing on the canister-integrated LDP, often after a rear-bumper repair that disturbed the unit. Common LDP repair pattern: replace pump + harness pigtail together; standalone pump replacement leaves the same root cause. Estimated repair: $200 to $750.