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Weak Vacuum Test

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

This tests for large leaks and blockages in the EVAP system. The PCM will command ON (close) the EVAP vent valve and command ON (open) the EVAP purge valve with the engine running, allowing engine vacuum into the EVAP system. The PCM monitors the Fuel Tank Pressure (FTP) sensor to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. If the PCM does not detect the predetermined vacuum level, a DTC P0440 (A large leak above 0.06" (1.5 mm) or blockage somewhere in the system) will set. To diagnose, go to SELF-DIAGNOSTICS - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.

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