P2406

P2406 means the ECM is seeing the LDP pressure-sense signal pinned at or above the upper voltage limit — typically over 4.8V when a working sensor should read 2.3-2.7V at atmospheric rest. The code indicates either an open signal-return (ground) circuit at the sensor, a short to the 5V reference on the signal wire, or a failed sensor that's internally collapsed to its supply rail. Expected scaling is 0.5-4.5V across -10 to +10 inH2O of EVAP pressure; a P2406 signature is a flat reading at 4.9-5.0V regardless of commanded pump activity. Cheapest-first ladder: back-probe the sensor ground pin and verify continuity to chassis ground (more than 0.5 ohms = open or high-resistance ground return), unplug the sensor connector and check whether the signal pin drops toward 0V (drops = sensor is the fault, stays high = harness short to 5V), and inspect the connector for a swapped pin or a pushed-back terminal. 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, because a green-rotted ground pin reads as open and sets P2406 even though the sensor and ECM are both good.

Vehicle-specific patterns: 1998-2009 VW/Audi (Jetta, Passat, Golf, A4, A6) throws P2406 from corroded ground-return pins inside the rear-axle LDP connector — the ground path opens up and the signal floats to reference voltage. 1998-2008 Chrysler/Jeep/Dodge (Sebring, Wrangler, Grand Cherokee) combined NVLD/LDP units throw P2406 from internal sensor failure that pins the output to the 5V rail. 1996-2005 Mercedes-Benz (W202, W203, W211) throws P2406 from a failed sensor ground splice inside the rear underbody harness — the splice is buried under a heat shield and frequently corrodes. Common LDP repair pattern: replace pump + harness pigtail together; standalone pump replacement leaves the same root cause. Estimated repair: $200 to $750.