P0440 -What Does It Mean? (1999-2006 V8 Chevrolet Silverado, GMC Sierra)

A P0440: Evaporative Emission Control System Malfunction is one of those trouble codes that tells you there's problem, just not what's causing it.

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 P0440 ¿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 P0440 Mean?

A P0440: Evaporative Emission Control System Malfunction means that there's a fuel vapor leak somewhere in the EVAP system.

Unfortuately, this trouble code does not pinpoint a specific component as the cause of the EVAP system failure.

Common Symptoms Of A P0440 Trouble Code

A P0440 will cause the vehicle to fail an emissions test. Usually, that's it.

Although a P0440 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 P0440 Trouble Code?

In most cases, a P0440 trouble codes appears after fueling the vehicle and not tightening the gas cap enough.

If the gas cap is nice and tight, the following can cause a P0440 trouble code to light up the check engine light:

• 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 P0440 Trouble Code

Repairing a trouble code P0440 involves finding and replacing the component with the fuel vapor leak.

The vacuum hose routing diagram (of your particular Chevrolet Silverado or GMC Sierra) will be a key source of information in checking the EVAP system components that are connectecd to engine vacuum.

Thankfully, this vacuum house routing diagram is found in your vehicle's engine compartment.

To find the component causing the P0440 trouble code, I recommend the following tests:

• Visually inspect the gas cap for damage or a worn gasket.
• Visually inspect all EVAP system hoses for damage/fuel/vacuum leaks.
• Check the operation of the EVAP purge valve solenoid.
• 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).