Check engine light always on

Asked by Feb 03, 2017 at 10:11 AM about the 2004 Chevrolet Monte Carlo LS

Question type: Maintenance & Repair

I have taken my car to AutoZone to get
the check engine light off they tell me it's
the gas cap and I need to replace it I
replaced it four times the check engine
light is still on. They say that it is a small
leak with the fuel pump I've tightened
everything down what else could it be
please help

3 Answers


You still have a problem with the EVAP system....P0442 CHEVROLET - Evaporative Emission Control System Leak Detected Small Leak...Possible causes; Missing or loose fuel cap, Incorrect fuel filler cap used, Fuel filler cap remains open or fails to close, Foreign matter caught in fuel filler cap, EVAP canister or fuel tank leaks, EVAP system hose leaking, Fuel tank leaking....The P0442 code means that the control module has detected a small leak in the Evaporative Emission (EVAP). Loose fuel tank filler cap is the most common cause that triggers the P0442 code......The Powertrain Control Module (PCM) tests the Evaporative Emission (EVAP) system for the following conditions: - Large and small leaks - Excess vacuum - Purge flow during non-commanded conditions - Fuel Level and Fuel Pressure sensor faults - EVAP Purge and Vent Valve faults The PCM monitors the Fuel Tank Pressure sensor in order to determine the level of vacuum/pressure in the EVAP system. The PCM commands both the EVAP Purge Solenoid and the EVAP Vent Valve ON when the conditions are met in order to apply an engine vacuum to the EVAP system. The PCM commands the EVAP Purge Solenoid OFF once the system has reached a predetermined level of vacuum. This test verifies if a vacuum can be achieved in the EVAP system. Failure to develop a vacuum may be caused by a large leak or a restriction.

3 of 3 people found this helpful.

right, gas cap is only one part of the EVAP system. Have a mechanic diagnose the issue, some Autozone techs know enough to sell you a part.

1 of 1 people found this helpful.

You'll need to have a smoke test done to find out exactly what's leaking and where. An EVAP system leak can be very small and unable to be seen with the naked eye. HTH. -Jim

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