P0442 on 2005-2007 Buick Terraza: Causes and Fixes for a Small EVAP Leak

What's Unique About the 2005-2007 Buick TERRAZA

The Buick Terraza and its GM U-body siblings (Chevy Uplander, Pontiac Montana SV6, Saturn Relay) were a unique 'crossover sport van' design. For this platform, a known and frequently-discussed issue is the location of the EVAP vent solenoid on top of the fuel tank, making it susceptible to road debris, moisture, and corrosion. This also makes replacement more labor-intensive than on many other vehicles, as the fuel tank must be partially lowered for access, a common frustration shared in owner forums.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• A faint smell of fuel (less common)
• Difficulty starting immediately after refueling (if the purge valve is stuck open)

Most Likely Causes

1. Loose, Worn, or Incorrect Gas Cap 🔴 High Probability → Shop Fuel Tank Cap The gas cap seal is a simple rubber component that degrades over time, leading to small leaks. It's the most frequently handled part of the EVAP system and the number one cause of P0442. 🎬 Watch: Two simple DIY methods to fix the P0442 code
   How to confirm: Ensure the cap is tightened until it clicks several times. Inspect the rubber O-ring seal for cracks, stiffness, or damage. Check the fuel filler neck for rust or debris that could prevent a good seal. Using a non-OEM cap can also cause this code.
   Typical fix: Tighten the cap. If the seal is bad or the cap is damaged, replace it with a new OEM-spec cap. Aftermarket caps are a frequent source of issues.
   Est. part cost: $15-$30
2. Faulty EVAP Vent Solenoid 🟡 Medium Probability → Shop Vapor Canister On the Terraza, this valve is located on or near the fuel tank, where it is exposed to road dirt, moisture, and corrosion, which can cause it to fail, clog, or for its rubber components to crack. It's a very common failure on this platform.
   How to confirm: Requires testing the solenoid's function with a scan tool or by applying 12v power to see if it actuates. A definitive diagnosis often requires a smoke test to see if the valve is leaking when it should be closed.
   Typical fix: Replace the vent solenoid. On this vehicle, this requires partially lowering the fuel tank for access. The wiring connector is also prone to corrosion and often needs to be replaced with a new pigtail harness (Part #19257603 or equivalent) at the same time.
   Est. part cost: $40-$100
3. Faulty EVAP Purge Valve/Solenoid 🟡 Medium Probability → Shop Vapor Canister Located in the engine bay, this valve is subjected to constant heat cycles which can cause it to fail, typically by getting stuck open or closed.
   How to confirm: Test the valve to see if it holds a vacuum when closed (engine off). A common symptom of a stuck-open purge valve is difficulty starting after refueling. Often seen with code P0496.
   Typical fix: Replace the purge valve. This is an easy DIY job located in the engine compartment.
   Est. part cost: $25-$50
4. Cracked or Disconnected EVAP Hoses/Lines ⚪ Low Probability Rubber and plastic lines can become brittle and crack with age and exposure to heat and the elements, especially rubber elbows and connectors.
   How to confirm: A visual inspection may reveal obvious cracks or loose connections. However, small leaks are often invisible and require a smoke test to locate precisely.
   Typical fix: Replace the damaged section of hose or reconnect it.
   Est. part cost: $10-$40

Rare But Worth Checking

• Leaking Charcoal Canister: → Shop Vapor Canister The plastic housing of the canister can develop small cracks over time. This is usually found with a smoke test.
• Leaking Fuel Tank or Filler Neck: → Shop Fuel Tank Rust can perforate the steel filler neck or the fuel tank itself, causing a leak. This is more common in regions that use road salt, and owners have reported this issue causing P0442.
• Faulty Fuel Tank Pressure Sensor: → Shop Fuel Tank The sensor that monitors EVAP system pressure can fail, providing incorrect data to the ECM. This usually sets a specific sensor-related code as well, but can occasionally contribute to a P0442.
• Leaking Fuel Pump Module Gasket/O-Ring: → Shop Fuel Pump The large O-ring that seals the fuel pump assembly to the top of the fuel tank can fail or be improperly seated after a fuel pump replacement, causing a small leak. A faint fuel smell inside the cabin might be noticeable.

Diagnosis Steps

1. Check for other stored DTCs that could provide more clues.
2. Inspect the gas cap. Remove it, check the seal for cracks, and clean the filler neck surface. Reinstall it and ensure it clicks multiple times. Consider replacing with an OEM cap if it is old or aftermarket.
3. Clear the code and drive for a few days to see if it returns. Many EVAP monitors only run under specific conditions.
4. If the code returns, perform a visual inspection of all accessible EVAP hoses and lines in the engine bay and under the vehicle, looking for obvious cracks or disconnections.
5. Test the purge valve in the engine bay. With the engine off, it should be closed and hold a vacuum. Try to blow through it; if air passes, it's faulty.
6. If the above steps do not reveal the issue, the most effective next step is to have a smoke test performed. This involves injecting smoke into the EVAP system to visually pinpoint the source of the small leak. This is the method recommended in manufacturer service information.
7. Based on the smoke test results, replace the leaking component, which could be the vent solenoid, a hose, the charcoal canister, or the fuel tank filler neck.

Parts You'll Likely Need

• Fuel Tank Cap (OEM #GT308) — This is the most common failure point due to frequent use and seal degradation. It's always the first part to check and replace.
  Trusted brands: ACDelco, Stant, Gates
  OEM price range: $20-$35
  Aftermarket price range: $15-$25
• Vapor Canister Purge Valve / Solenoid (OEM #214-1473) — This part is located in the hot engine bay and can fail by sticking open or closed. It's a common cause for P0442, especially if code P0496 is also present.
  Trusted brands: ACDelco, Standard Motor Products, Dorman
  OEM price range: $40-$60
  Aftermarket price range: $25-$45
• Vapor Canister Vent Valve / Solenoid (OEM #214-2324) — Its location near the fuel tank makes it prone to damage from road debris and moisture, causing it to leak or fail. This is a highly likely culprit if the gas cap and purge valve are good.
  Trusted brands: ACDelco, Standard Motor Products, Dorman
  OEM price range: $50-$80
  Aftermarket price range: $40-$60
• Vent Solenoid Wiring Harness Pigtail (OEM #19257603) — The original connector for the vent solenoid often corrodes or becomes brittle, requiring replacement when the solenoid is changed. Some replacement solenoids have a different connector design and come with this harness.
  Trusted brands: ACDelco, Dorman, Michigan Motorsports
  OEM price range: $20-$30
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0455 — This code indicates a large EVAP leak. Both P0442 and P0455 can be triggered by similar faults, and TSB 21-NA-124 addresses diagnostics 🎬 Watch: A breakdown of common causes and fixes for P0442 for both codes together.
• P0496 — Indicates 'EVAP Flow During a Non-Purge Condition,' which almost always points directly to a faulty purge valve that is stuck open.
• P0449 — This code points to a fault in the EVAP vent solenoid's electrical circuit, which can appear if the vent solenoid itself has failed electrically or if its connector is corroded.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-124: Provides diagnostic tips for testing EVAP leaks causing P0442 and/or P0455. It applies to a wide range of GM vehicles from 2000-2023.
• PIT4943D: Instructs technicians on using an EVAP system tester (smoke machine) to diagnose P0442, referencing a Techlink article from May 2013.

Platform-Specific Known Issues

• Per TSB #21-NA-124, GM provides specific diagnostic tips for finding EVAP leaks related to codes P0442 and P0455. The recommended order is to first check all EVAP lines for secure connections and damage, then investigate the vent valve for malfunction, and finally check the purge valve.
• TSB #PIT4943D directs technicians to use an Evaporative Emissions System Tester (a smoke machine) to properly diagnose code P0442, highlighting that visual inspection alone is often insufficient.

Mechanic-Grade Diagnostic Values

• EVAP Purge or Vent Solenoid Coil Resistance — expected: 14 to 30 Ohms. Failure: A reading of 0 Ohms (short circuit) or infinite/OL (open circuit) indicates a failed solenoid coil. One source specified 20-30 Ohms.
• EVAP Vent Solenoid Connector Voltage — expected: 11V to 18V (Battery Voltage). Failure: No voltage at the power feed wire with the ignition on points to a wiring or fuse issue, such as the CNSTR/VENT 10A fuse.

Scan Tool Commands That Help

• Tech II / GDS2 (or equivalent bidirectional scanner): EVAP System Seal / Vent Valve Close — This command is required to electronically close the normally-open vent solenoid. This seals the EVAP system, which is a necessary step before performing a smoke test to find the source of a P0442 leak.
• Tech II / GDS2 (or equivalent bidirectional scanner): EVAP Purge/Seal Test — This automated test commands the purge and vent valves to cycle while monitoring the Fuel Tank Pressure (FTP) sensor to check for leaks and proper component function, as described in the DTC setting criteria.

Wiring & Ground Locations

• EVAP Canister Vent Solenoid — Above the fuel tank, typically accessible from under the passenger side of the vehicle.. This is the physical location of the component most likely to fail after the gas cap. Knowing its location is key for inspection and replacement.
• EVAP Canister Purge Solenoid — In the engine compartment, mounted on the engine or near the intake manifold on the driver's side.. This is the location of the second most common solenoid to fail. It is easily accessible for testing and replacement.
• Fuel Tank Pressure (FTP) Sensor — On top of the fuel tank, part of the fuel pump module assembly.. This sensor provides the pressure readings the ECM uses to detect the P0442 leak. A faulty sensor or a leak at its seal can cause the code.
• CNSTR/VENT Fuse 19 (10A) — In the I/P (Instrument Panel) fuse block, located on the right side of the dash behind an access panel.. This fuse supplies power to the EVAP canister vent solenoid. If this fuse is blown, the solenoid will not operate, which can lead to EVAP codes.

Real Owner Repair Stories

• GM Forum user Bretton65 (Buick (model not specified, but forum context implies a 2000+ GM vehicle)) — P0442 Check Engine Light, gasoline smell near the fuel tank area.
  ❌ Tried (didn't work) Replaced vapor canister purge valve, Replaced canister vent solenoid
  ✅ What actually fixed it The final fix was replacing the fuel tank pressure sensor and, crucially, the fuel pump "sending unit" gasket (O-ring). The user suspected the gasket was the true cause due to the gas smell, which disappeared after replacement.

"I Checked Everything" — The Actual Cause

• A smoke test may show no external leaks, but the code can still be caused by an internally leaking EVAP purge valve. The valve is normally closed, but if it fails to seal properly, it allows un-commanded vacuum into the EVAP system from the engine intake. This can be diagnosed by applying vacuum to the valve when it's de-energized to see if it holds, or by observing hard starting after refueling.

OEM Part Supersession History

• 12581282 → 214-1473 (ACDelco) — Part number consolidation and potential design updates.
  Heads up: This is the Vapor Canister Purge Valve. Multiple older part numbers like 12573220 and 12581282 are superseded by the current ACDelco number.

Model Year Variations Within This Range

• 2005-2007: The Terraza was offered with a 3.5L V6 (2005-2006) and a 3.9L V6 (2006-2007). While the core EVAP components and part numbers are generally the same, the engine control computer may be designated differently (PCM for 3.5L, ECM for 3.9L) and the exact mounting location of the engine-bay purge valve can vary slightly between the two engines.
• 2005-2007: These vans were produced in short-wheelbase (SWB) and long-wheelbase (LWB) versions. While this doesn't affect the common causes of P0442, it is critical for ordering correct replacement parts for the rear of the vehicle, such as the vapor canister assembly, as different part numbers are used for each wheelbase.