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Discussion Starter #1
Hello everyone,
So I had thought after last fix, I won't be posting regarding same issue. But that is not so. :-(


Evey other day mostly close to 24 hrs after reset, check engine light comes on again. Code on scanner, MIL/FTC/Perm/Present is P0455 Large leak detected.
I reset it, and wait for it to reappear the next day. Sometimes 2 days. And now every 4 to 5 days, P4096 Small leak detected. When the small leak detects, the large leak code don't appear.


So far, I have replaced, throttle body with new BOSCH unit, purge valve solenoid with new ACDelco unit, and Charcoal canister solenoid and new wiring harness with ACDelco genuine parts.
Cadillac of Ann Arbor MI ran a smoke test and found no leaks.
What gives????????
Thanks again in advance for all your help.
Engine 3.0 liter v6 Performance Edition AWD.
 

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I would check every hose associated with that evap system for a pin hole leak or crack especially where they slide on to a connector. Saw that problem on a Chrysler town and country not too long ago. The crack was not evident until I pulled on the hose then bingo there it was.
 

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Common causes of these two codes are:

Fuel cap or filler neck seal surface
Fuel tank pressure sensor
Restrictions to the purge path in the EVAP system

These codes can be hard to diagnose because the fault can only present itself under a vacuum.
Use a scanner with the Purge/Seal function to create a vacuum in the EVAP system and then observe the FTP sensor parameter for vacuum decay.
Information from the 2014 GM Repair Manual.
 

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Discussion Starter #4
Thanks guys.

I'll check all hoses next. Do not have a scanner that will create a purge /seal, so I guess that will be a dealer or hopefully mechanical shop look-see. Kind of hard to do with that venue being my only daily driver, and shops love to "Drop it off and we'll get to it" scenario. Hopefully will find a leaking hose...Cause my OBD2 scanner can reset idiot light but can't create a vaccum/seal.
 

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Had small leak code on an old caravan. Could not see and issues with the hoses. Until a mechanic neighbor came over and showed me to squeeze the hoses...bingo queezing the hoses exposed a crack in the hose connected to the air filter box not seen with the eye.
 
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