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P0172/P0175/P0496 - 2008 Chevrolet Suburban LTZ 5.3L V8 with Flex Fuel: EVAP System and Lean/Bank Issues

Model: 2008 LTZ Chevy Suburban 4WD Fault Code: P0172 Posted: 2015-11-20 15:23

2008 Chevrolet Suburban LTZ 5.3L V8 (Flex-Fuel) - I recently experienced check engine light activation with diagnostic codes P0172 (System Too Lean Bank 1), P0175 (System Too Rich Bank 2), and P0496 (EVAP System Flow During Non-Purge). I initially used top-tier fuel additive (Supreme) and replaced the purge solenoid (Bank 1), as it was accessible. Afterward, I confirmed the gas cap was properly sealed and replaced the vapor canister and vent solenoid hose. The engine light cleared for approximately two months before returning with P0172 and P0496. I inspected all hoses connected to the purge system and found no visible damage or leaks. Given that the issue persists, I am now considering cleaning or replacing the Mass Air Flow (MAF) sensor, performing a tune-up including spark plug replacement, or installing a new air filter. I have already used fuel additive in the tank, which temporarily resolved the issue for about five days before it returned. I am not a certified mechanic and rely on YouTube tutorials to maintain my vehicle. I also own a 1972 Chevelle that I use for hands-on experience. Any advice or troubleshooting steps would be greatly appreciated. Thanks in advance! Note: The vehicle is stock with no aftermarket modifications.

Related fault codes

P0172P0175P0496

Comments (4)

Anonymous 2015-11-20 16:13

DTC P0172 indicates a lean fuel condition in Bank 1; DTC P0175 shows a rich condition in Bank 2. The presence of both codes suggests an EVAP system issue, not just a fuel trim problem. P0496 specifically points to an EVAP system flow anomaly during non-purge cycles — this is typically caused by vacuum leaks past the purge solenoid valve. Before addressing fuel trims or sensors, ensure there are no unintended vacuum connections downstream of the purge valve. Avoid using premium additives like Supreme in Flex-Fuel vehicles as they may interfere with EVAP system operation. Never top off the fuel tank after the pump shuts off — this can introduce air into the fuel line and affect purge function. Please confirm your vehicle is stock (no aftermarket parts) to ensure accurate troubleshooting.

Anonymous 2015-11-21 08:27

You mentioned replacing the purge solenoid (Bank 1). Could you clarify whether you replaced the purge solenoid or the oxygen sensor? Misdiagnosis here could lead to incorrect repairs and recurring codes.

Anonymous 2015-12-11 08:43

Cedric, have you found a resolution for your P0496/P0175/P0172 issue? I'm experiencing the same symptoms on my 2008 Suburban LTZ. I use Super Unleaded — should I stop using it? I've also topped off the fuel tank after the pump stopped, and filled up while the engine was running — could this be contributing to P0496? Any insight would be helpful.

Anonymous 2015-12-11 09:27

Using Super Unleaded is unnecessary and costly for a Flex-Fuel vehicle. It may disrupt fuel system chemistry and interfere with EVAP function. Never top off the tank after the pump stops — doing so introduces air into the fuel system, which can damage the purge valve and trigger P0496. Filling up while the engine is running is also not recommended; it can cause vapor lock or air ingestion. As a guess: Do you use a K&N air filter? If so, ensure it's compatible with your vehicle’s emissions system to avoid interfering with airflow and sensor readings.