P0442 on 2011-2018 Cadillac CTS: EVAP Small Leak Causes and Fixes

What's Unique About the 2011-2018 Cadillac CTS

The 2011-2018 Cadillac CTS spans two vehicle generations: the second-gen (2011-2014, Sigma II platform) and the third-gen (2014-2019, Alpha platform). While the function of the EVAP system is the same, the location and part numbers for components like the purge and vent valves can differ. The 3.6L V6 engine (LFX) is common across this range and is known for issues with the purge valve. 🎬 Watch: Step-by-step purge valve replacement for the 3.6L V6 engine. GM has issued technical service bulletins for this code on related vehicles, suggesting diagnosis can be complex. TSB PIT4943D, for example, details a specific diagnostic process using a scan tool and smoke machine, indicating that simply replacing parts is not always effective.

Diagnostic Flowchart

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

Generation note: This range covers the end of the second generation (2011-2014) and the third generation (2014-2019). The EVAP purge valve is a very common failure point on the 3.6L V6 engine used in both generations. However, always verify part numbers for your specific year, as component designs and locations may have changed. For many 3.6L V6 models in this range, the ACDelco purge valve part number is 12610560 (superceded by 12690512). The location of the purge valve moved from the driver's side of the engine on the first generation to the passenger's side for the second generation (2008-2014).

Symptoms You May Notice

• Check Engine Light is on
• A faint fuel smell (less common).
• Difficulty starting the car immediately after refueling (points to a stuck-open purge valve).
• Rough idle or change in engine performance if the purge valve fails and creates a vacuum leak.

Most Likely Causes

1. Loose or Faulty Gas Cap 🔴 High Probability The gas cap seal is a rubber component that degrades over time, leading to small leaks. It's the most common and easiest-to-fix cause for a P0442 code on any vehicle. Using a non-OEM cap can also cause sealing issues.
   How to confirm: First, ensure the cap is tightened until it clicks at least once. Inspect the rubber gasket on the cap for cracks, stiffness, or damage. Check the fuel filler neck for rust or debris that could prevent a good seal. A temporary test can be done by wrapping the cap's seal with a plastic bag to see if the code clears after a drive cycle.
   Typical fix: Replace the gas cap. It is often recommended to use an OEM (Original Equipment Manufacturer) part, such as ACDelco, to ensure a perfect seal.
   Est. part cost: $15-$40
2. Faulty EVAP Purge Valve/Solenoid 🔴 High Probability This valve is a known common failure item on many GM vehicles with the 3.6L V6 engine, including the CTS. It can get stuck open, allowing un-metered fuel vapors into the intake and creating a vacuum leak.
   How to confirm: A stuck-open purge valve often causes hard starting and rough running after refueling. The valve is normally closed. To test, remove it from the engine (usually located on the intake manifold), and try to blow through it. If air passes through, it has failed and is stuck open. This failure often triggers P0496 alongside P0442.
   Typical fix: Replacement of the purge valve is straightforward. It is located on top of the engine and held by one 10mm bolt. The OEM part is often ACDelco #12610560 or its replacement, #12690512.
   Est. part cost: $25-$60
3. Faulty EVAP Vent Valve/Solenoid 🟡 Medium Probability A GM service bulletin (21-NA-124) notes that a leaking EVAP vent solenoid can be a cause for P0442. This valve is normally open and closes to allow the system to be pressure tested. It can get stuck or fail to seal completely due to dirt, dust, or corrosion.
   How to confirm: This part is harder to access, usually located near the EVAP canister by the fuel tank. Testing often requires a scan tool to command the valve closed and a smoke machine to see if it's leaking. TSB 21-NA-124 recommends checking lines and connections before suspecting the vent or purge valves.
   Typical fix: Replace the vent valve solenoid. This may require lowering the rear subframe or fuel tank for access.
   Est. part cost: $30-$55
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability Rubber hoses and plastic lines can become brittle and crack over time due to heat and age. A YouTube video of a 2014 CTS with P0442, P0171, P0174, and P0496 showed the cause was a combination of a bad purge valve and a cracked vacuum boot on a line in the engine bay.
   How to confirm: A visual inspection may reveal obvious cracks or loose connections, particularly on the lines connected to the purge valve on top of the engine. However, small leaks often require an EVAP smoke test to find, where smoke is fed into the system and the technician looks for where it escapes.
   Typical fix: Replace the damaged hose or connector.
   Est. part cost: $10-$50

Rare But Worth Checking

• Leaking EVAP Canister: The plastic housing of the charcoal canister can develop hairline cracks, causing a small leak. This is usually found with a smoke test after other common causes have been ruled out. One detailed diagnostic video on a related Cadillac SRX showed a brand new, defective canister leaking from a seam.
• Faulty Fuel Tank Pressure Sensor: If the sensor that measures pressure in the EVAP system provides incorrect readings, it can trick the computer into thinking there is a leak when there isn't one. This is uncommon and usually accompanied by other codes.

Diagnosis Steps

1. Inspect the gas cap for damage and ensure it is tightened properly. If in doubt, replace it with an OEM part, clear the code, and drive for a few days to complete a drive cycle.
2. If the code returns, perform a thorough visual inspection of all accessible EVAP hoses and lines under the hood, especially those connected to the purge valve, for obvious cracks or disconnections.
3. Locate the EVAP purge valve on the engine's intake manifold. If you experience hard starting after refueling, this part is highly suspect. Remove it and try to blow through the port that comes from the EVAP canister; if air passes, the valve is bad and needs replacement.
4. If the previous steps do not reveal the issue, the most effective next step is to have a professional perform an EVAP smoke test. This test will push low-pressure smoke through the system, making even the smallest leaks visible.
5. Based on the smoke test results, replace the leaking component, which could be the vent valve, EVAP canister, or a cracked hose. TSB #PIT4943D provides a detailed procedure for technicians to follow to isolate the leak using a scan tool and smoke machine.

Parts You'll Likely Need

• Fuel Cap (OEM #ACDelco GT295 (Example, verify by VIN)) — This is the most frequent and simplest fix for a P0442 code. The seal wears out over time. Using an OEM cap is highly recommended.
  Trusted brands: ACDelco, Motorad
  OEM price range: $20-$40
  Aftermarket price range: $15-$25
• Vapor Canister Purge Valve / Solenoid (OEM #ACDelco 12610560 (superseded by 12690512)) — A very common failure point on GM 3.6L V6 vehicles that causes P0442 and P0496. It gets stuck open, allowing un-metered vapor into the engine.
  Trusted brands: ACDelco, Bosch, Dorman
  OEM price range: $40-$70
  Aftermarket price range: $25-$50
• Vapor Canister Vent Valve / Solenoid (OEM #ACDelco 214-2324 (Example, verify by VIN)) — This valve, located near the fuel tank, can fail to seal properly during the EVAP self-test, causing a small leak. A GM TSB points to this part as a possible cause after checking hoses.
  Trusted brands: ACDelco, Dorman, Standard Motor Products
  OEM price range: $45-$65
  Aftermarket price range: $30-$55

Related Codes That Often Appear With This One

• P0455 — This code indicates a large EVAP leak. It can appear with P0442 if the leak is intermittent or on the borderline between small and large. TSB #21-NA-124 specifically mentions diagnosing P0442 and/or P0455 together.
• P0496 — This code means 'EVAP Flow During a Non-Purge Condition' and almost always points directly to a faulty EVAP purge valve that is stuck open or leaking internally. If you have P0496 with P0442, the purge valve is the primary suspect.
• P0171 / P0174 — These 'System Too Lean' codes can be caused by a vacuum leak. If the EVAP purge valve is stuck open, it can create a vacuum leak that affects the engine's air-fuel mixture, triggering these codes alongside the P0442. A 2014 CTS owner documented this exact combination of codes being caused by a bad purge valve and a cracked vacuum line.

Technical Service Bulletins (TSBs) & Recalls

• PIT4943D: Directs technicians to use an Evaporative Emissions System Tester for diagnosis of P0442, providing a step-by-step process to isolate leaks in the purge solenoid versus the rest of the system.
• 21-NA-124: Provides diagnostic tips for testing EVAP leaks related to DTCs P0442 and/or P0455, recommending inspection of lines first, followed by the vent valve, then the purge valve.

Platform-Specific Known Issues

• TSB #21-NA-124 provides diagnostic tips for technicians dealing with P0442 and/or P0455. It advises a specific order of operations: 1) check all EVAP lines are seated and undamaged, 2) investigate the vent valve, and 3) investigate the purge valve.
• TSB #PIT4943D refers technicians to a specific Techlink article from May 2013 for advanced diagnostics using an evaporative emissions system tester, highlighting that this code can require more than simple part swaps.

Mechanic-Grade Diagnostic Values

• EVAP Purge Valve Solenoid Resistance — expected: 20 - 30 Ohms. Failure: A reading that is too high, too low, or infinite (open circuit) indicates a faulty valve.
• Fuel Tank Pressure (FTP) Sensor Voltage — expected: Approximately 1.5V with the gas cap off (atmospheric pressure). The voltage should change as pressure/vacuum is applied.. Failure: A sensor that is stuck at a high or low voltage, or does not respond to pressure changes, is faulty. One owner reported a sensor stuck in a negative voltage reading which was resolved by replacement.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): EVAP Service Bay Test — This is a technician-level function used to command the EVAP system into a test state. It allows the user to close the vent solenoid and command the purge solenoid on/off to check for leaks and proper valve function, which is essential for diagnosing a P0442.
• GDS2 (GM Global Diagnostic System 2): Purge Solenoid Control — This bidirectional control allows a technician to manually open and close the purge solenoid while monitoring fuel tank pressure data. If the system pressure doesn't change when the valve is commanded, or if it changes when the valve is commanded closed (indicating a leak), it points to a faulty valve.

Wiring & Ground Locations

• EVAP Canister Vent Solenoid Valve — On the evaporative emission canister, which is typically located near the fuel tank, under the rear of the vehicle.. This valve must seal correctly for the EVAP system to hold pressure. A poor connection or damaged wiring at this location can prevent the valve from closing, causing a P0442 leak code.
• Fuel Tank Pressure (FTP) Sensor — For a 2014 CTS, wiring diagrams show it at the rear of the right rear wheelwell. A repair video for a 2008 model shows it accessible by going straight up from the passenger side rear wheel.. This sensor provides the pressure reading to the ECM. If its wiring is damaged or its ground is poor, it can send false signals, leading to an incorrect P0442 code.
• G107 (Ground) — On the engine block, near the ignition coils (for a 2003 model, but locations are often similar).. The Engine Control Module (ECM) and its related sensors require a solid ground reference. A loose or corroded engine ground can cause erratic sensor readings and incorrect diagnostic codes.
• Cnstr/Vent Fuse — In the underhood fuse block (for a 2014 model).. This 10A fuse provides power to the EVAP canister vent solenoid. If this fuse is blown, the vent valve may not operate correctly, leading to a failed EVAP test and a P0442 code.

Real Owner Repair Stories

• YouTube video from 'The Flat Rate Mechanic' (Vehicle with GM 3.6L engine) — Check Engine Light with codes P0442 and P0496.
  ❌ Tried (didn't work) The video focuses on direct diagnosis rather than failed attempts.
  ✅ What actually fixed it The diagnosis confirmed a bad EVAP purge valve. The technician demonstrated that with the valve removed from the car, he was able to blow air through it, proving it was stuck open. Replacing the purge valve fixed the issue.

"I Checked Everything" — The Actual Cause

• In a diagnostic video for a persistent P0442, the technician notes that intermittent solenoids (purge or vent) can be a cause. The solenoid may pass a test at one moment but stick just enough to fail the vehicle's self-test later. He mentions that running the scan tool's bidirectional test on the solenoid multiple times (8-10 times) can sometimes force an intermittent failure to reveal itself.

When the Usual Fixes Don't Work

• While a faulty gas cap is a very common cause, it will not typically trigger a P0496 (EVAP Flow During Non-Purge Condition) code. If P0442 is present alongside P0496, the focus should immediately shift to the EVAP purge valve, as it is the most likely component to cause both codes simultaneously.

OEM Part Supersession History

• ACDelco 12610560 → ACDelco 12690512 — Standard part lifecycle update by the manufacturer.
  Heads up: No known incompatibility issues; 12690512 is the direct replacement for 12610560 for the specified applications.

Model Year Variations Within This Range

• 2011-2014 (Second Gen) vs 2014-2018 (Third Gen): The 2011-2014 models are on the Sigma II platform, while the 2014+ models are on the Alpha platform. This major platform change means component locations, wiring harnesses, and some part numbers are different. For example, the EVAP canister replacement cost and labor time is significantly different between a 2013 and a 2014 model, indicating a different design and location. The purge valve location also changed between generations, moving from the driver's side to the passenger's side of the engine.