P2405

P2405 means the ECM is seeing the LDP pressure-sense signal pinned at or below the lower voltage limit — usually under 0.2V when a working sensor should be reading 2.3-2.7V at atmospheric rest. The code typically indicates a short to ground on the signal wire, a failed sensor element that's collapsed to ground, or an open 5V reference upstream of the sensor that's left the signal pulled to chassis through the sensor's internal divider. The expected behavior is 0.5-4.5V scaled across -10 to +10 inH2O of EVAP pressure; a P2405 signature is a flat 0.0-0.2V reading with no movement during commanded pump cycles. Cheapest-first ladder: back-probe the 5V reference pin at the sensor and verify 4.95-5.05V (no reference = ECM-side fault or shared-reference short on another sensor that's pulling the whole rail down), unplug the sensor and check whether the signal pin rises to the ECM bias level (rises = sensor is internally shorted, stays at 0V = harness short to ground), and visually inspect the signal-wire run for chafe-through against the chassis. 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 remember that a shared 5V reference pulled down by another sensor (often a fuel-tank pressure sensor on the same bus) will set P2405 alongside other low-voltage codes — diagnose the cluster, not the single code.

Vehicle-specific patterns: 1998-2009 VW/Audi (Jetta, Passat, Golf, A4, A6) throws P2405 from water intrusion that bridges the signal pin to the connector shell ground inside the rear-axle LDP housing. 1998-2008 Chrysler/Jeep/Dodge (Sebring, Wrangler, Grand Cherokee) NVLD/LDP combination units throw P2405 from an internally-shorted pressure transducer — the unit is non-serviceable. 1996-2005 Mercedes-Benz (W202, W203, W211) throws P2405 from a chafed signal wire where the EVAP loom passes the rear muffler hanger, with the wire grounding to the exhaust shield. Common LDP repair pattern: replace pump + harness pigtail together; standalone pump replacement leaves the same root cause. Estimated repair: $200 to $750.