Case Study: P2404 - - EVAP Leak Detection Pump Sense Circuit: Implausible Signal

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The subject:
2006 A4 with 2.0 BPG engine

The victum:
Chad Z who hails from beautiful downtown North Ridgeville, OH... Cleveland Magazine's June 2002 pick for "best festival in Northeast Ohio"!!!!

2006 A4, keeps flagging the P2404 - - EVAP Leak Detection Pump Sense Circuit: Implausible Signal. Prior to calling, Chaz had ohm tested the LDP (V144):

/1 + /3 = 680Ω
/2 + /3 = 16Ω

These values are to factory design. Loaded tested voltage on wiring harness with light bulb on wiring harness /3, carries load, no signs of voltage drop.

Go to do Basic Settings 071, fuel tank has 1/4 tank. Test fails within 10 seconds, very fast for a failure. I request Chad check for vacuum supply to the LDP (V144) with the engine at idle. No vacuum.

Look in engine bay for a vacuum check valve and nipple, close to brake booster... and this is found:


Photo credit to Chad Z, Hasselblad H6D-400c MS 1/850 @ f5.6

Well, that sucks... or rather not at the LDP (V144).

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2010 Tiguan with a 2.0T CCTA engine. Same P2404 fault code. LDP been replaced, wiring looked over, just can't find anything wrong with it.

Do you have engine vacuum at the LDP? .... eh... no, I don't. Back in the engine bay, found vacuum line disconnected. Hooked it up, vacuum at LDP now.

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A rather rare documented test for the LDP, pinch off the vent line (filter) of the LDP and then manually apply vacuum 0.700 BAR (20" of Merc) and verify it holds. I've now had 2 cases where the LDP ohm out to spec (same as above) and had good vacuum supply to the pump as well, but the LDPs would not hold vacuum. One shop has called back and verified the replacement LDP did hold vacuum.