P0442 -What Does It Mean? (1999-2006 V8 Chevrolet Silverado, GMC Sierra)

A trouble code P0442: EVAP System Leak Detected tells you there's an EVAP system leak, just not where it's at.

In this tutorial, I'll shed some light on what this trouble code means and some of the tests you can perform to find its cause (and solution) in case a loose gas cap is not the source of the problem.

You can find this tutorial in Spanish here: Código P0442 ¿Qué Significa? (1999-2006 V8 Chevrolet Silverado, GMC Sierra) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

Chevrolet:

• 4.8L Chevrolet Silverado (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 5.3L Chevrolet Silverado (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 6.0L Chevrolet Silverado (2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

GMC:

• 4.8L GMC Sierra (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 5.3L GMC Sierra (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 6.0L GMC Sierra (2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

What Does Trouble Code P0442 Mean?

A P0442: EVAP System Leak Detected tells you that your Silverado or Sierra's fuel injection computer has pressurized the EVAP system to test for leaks and has found one.

This EVAP system leak will cause fuel vapors to escape into the atmosphere.

Unfortuately, this trouble code does not pinpoint a specific component as the cause of the EVAP system's fuel vapor leak.

Common Symptoms Of A P0442 Trouble Code

A P0442 will cause the vehicle to fail an emissions test. Usually, that's it.

Although a P0442 will cause your Silverado (Sierra) to fail an emissions test, the EVAP system problem causing it generally does not cause any driveability issues.

Generally the only other problem, besides a failed emission test, is the check engine light shining nice and bright on the instrument panel.

What Does The EVAP System Do?

The purpose of the evaporative emission control (EVAP) system is to capture the fuel tank vapors and prevent them from escaping into the ambient air (the atmosphere).

The EVAP system, on the Chevrolet Silverado (GMC Sierra), consists of:

• Fuel tank.
• EVAP vent solenoid.
• Fuel tank pressure sensor.
• Fuel pipes and hoses.
• Vapor lines.
• Gas cap.
• EVAP emission canister (charcoal canister).
• Purge lines.
• EVAP purge solenoid.

What Causes A P0442 Trouble Code?

Generally, a P0442 trouble code is caused by a loose gas cap (one that wasn't tightened enough after fueling the vehicle).

If a loose gas cap is not the problem, then the following problems could be causing the P0442 trouble code:

• Damaged/incorrect gas cap.
• Damaged/leaking EVAP system hose.
• Bad canister purge control valve.
• Damaged/broken EVAP emission canister (charcoal canister).
• Damaged/leaking fuel tank.
• Leaking fuel tank hoses.

How To Diagnose And Repair A P0442 Trouble Code

Repairing a trouble code P0442 involves finding and replacing the EVAP system component that's causing the fuel vapor leak.

For the DIY'er, finding the EVAP leak can be a challenge without a 'smoke machine' and a professional level scan tool (that has live data capability and the ability to activate the EVAP system components).

In case you're wondering, the smoke machine is designed to pump smoke made from mineral oil into the EVAP system. Wherever the leak is at, the smoke will come out.

Unfortunately, depending on how small and where the leak is at, the smoke machine may be of no help at all (this happens quite often).

If you don't have access to a smoke machine, I recommend testing the gas cap, EVAP vent solenoid, and the EVAP purge solenoid (since they are the most common causes of a P0442 trouble code).

To be a bit more specific:

1. Visually inspect the gas cap for damage or a worn gasket.
2. Visually inspect all EVAP system hoses for damage (like cracks, missing hose clamps, etc.).
3. Check the operation of the EVAP purge solenoid.
   • What you're looking for is for the purge solenoid to be closed and not letting any air thru' it.
4. Check the operation of the EVAP vent solenoid.
   • What you're looking for is for the vent solenoid to be closed (when activated) and not letting any air pass thru' it.
   • You can find the EVAP vent solenoid test here: How To Test The EVAP Vent Solenoid (1999-2002 V8 Chevrolet Silverado, GMC Sierra).
5. Visually inspect the EVAP carbon canister for damage.

Replace any component that is damaged.

In some cases, the fuel tank has to be lowered (and possibly removed) to check:

• Fuel lines: These are the fuel lines that connect to the fuel tank sending unit.
• EVAP system hose: This is the vapor hose/line that connects to the fuel tank sending unit (this hose/line is the one that carries the fuel vapors to the EVAP emission canister).
• Fuel tank sending unit gasket: This is the gasket that sits between the fuel sending unit assembly and the gas tank. Check it for cracks and/or damage.
• Fuel tank pressure sensor: This is the sensor that measures the fuel tank pressure and if there's any loss (of pressure) tells the fuel injection computer that there's a leak in the EVAP system.
• Fuel filler hose: This hose connects the fuel filler neck to the gas tank and has two hose clamps that should be check for looseness.

More Chevrolet Silverado (GMC Sierra) Tutorials

You can find a complete list of V8 Chevrolet Silverado (GMC Sierra) tutorials in this index:

• GM 4.8L, 5.3L, 6.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• Resistance Specifications Of The TAC Electronic Throttle Body.
• How To Test The GM Accelerator Pedal Position (APP) Sensor 2.
• How To Test The MAF Sensor (GM 4.8L, 5.3L, 6.0L, 8.1L).
• Blown Head Gasket Test (GM 4.8L, 5.3L, 6.0L).