Common Check Engine code reference for Honda/Acura

These codes indicate a misfire on a specific cylinder (e.g., P0301 is cylinder #1, P0304 is cylinder #4). On Honda/Acura 3.0L and 3.5L V6 engines, this is widely known to be caused by buildup on the spark plugs directly resulting from VCM (Variable Cylinder Management) operation.

Over time, the buildup of uncombusted fuel and oil in deactivated cylinders causes micro-abrasions on the cylinder walls. This leads to high oil consumption and lower compression, typically manifesting in the 40k–50k mile range. Many mechanics speculate that during cylinder deactivation, engine vacuum starves the deactivated cylinders of necessary oil and lubrication.

VCM-1 Engines (2005-2007 3.5L V6): Deactivates cylinders 1-3. Because only half the cylinders are deactivated, oil consumption and misfire issues usually present later, around the 100k mile range.

VCM-2 Engines (2008+): Deactivates cylinders 1-4. Due to this aggressive programming, vehicles exhibited high oil consumption as early as 10,000 miles, ultimately leading to the Honda engine misfire class-action settlement in 2013/2014.

These codes indicate a Rocker Arm Oil Pressure Switch issue:

• P3400: VPS stuck off (Bank 1)
• P3497: VPS stuck off (Bank 2)

1. Check the engine oil level. Low oil pressure can trigger these codes. If low, top off or replace the oil, and refer to Honda Service Bulletin (S/B) 11-033 regarding engine oil consumption.
2. If the oil level is fine, clear the codes and turn the ignition switch to ON (without starting the engine). If the codes return immediately, the rocker arm oil pressure switch circuit is likely faulty.
3. Unplug the affected switch connector. Check the signal on the PGM-FI Data List. If the signal reads OFF, the wiring is okay, and the switch itself needs replacement. If the signal reads ON, there is a wiring or PCM problem.

This code indicates that the catalytic converter is operating below normal efficiency. On a VCM-equipped Honda, this code is typically the direct result of uncombusted fuel and oil passing into the catalytic converter. The precursor to this code is almost always engine misfires on VCM-affected cylinders (P0301-P0304).

• Debris Buildup: The converter is filled with soot from high oil consumption caused by ring wear and VCM operation.
• Aged O2 Sensors: Worn sensors (5-10 year lifespan) cause the air-to-fuel ratio to run too rich.
• Worn Converter: The EPA rates the useful life of a catalytic converter at roughly 100,000 miles or 10 years.

1. Disable VCM: Install a VCMTUNER or VCMTUNER II to stop the oil consumption and spark plug fouling that destroys the catalytic converter.
2. Check Spark Plugs: Only use genuine NGK Iridium plugs. If they are covered in black soot, replace them immediately.
3. Cleaners (Use Caution): Additives like Cataclean may help clear minor buildup. However, use caution: products like SeaFoam (which is oil-based) can sometimes gum up the catalyst honeycomb or dislodge carbon deposits that further damage O2 sensors. We recommend driving the vehicle rigorously at 3k-4k RPM in a lower gear to assist in naturally blowing out deposits.
4. Replacement: If oil consumption is under control but the code persists, you likely need a new catalytic converter ($800–$1,500+ depending on state emissions laws).

This code relates to the ECT1 sensor. It triggers if the vehicle fails to reach 160°F during two consecutive drive cycles. If you are not using a VCM disabling device, this usually points to a stuck-open thermostat.

If you are using a dial-based VCM disabling device, this means the resistance is set too high and the reported temperature is below 160°F. This prevents the vehicle from entering "closed loop" mode (158°F+), forcing it to run in "warm-up" mode, which causes poor gas mileage.

Note: The VCMTUNER II avoids this entirely by dynamically adjusting the resistance to maintain a perfect 163°F–165°F.

This code triggers if the ECT1 circuit is disconnected while the ECU is monitoring it. This frequently occurs during the physical installation of a VCM disabling device. Once the installation is complete and the connection is secure, this code will clear itself after a few normal drive cycles.

This code triggers if the 12v connection to the VCMTUNER II is disconnected while the ECU is active. It can also indicate a bad or intermittent connection at the ECT sensor.

In rare circumstances, this code can occur if the VCMTUNER II experiences a massive ESD startup surge (often from a non-OEM starter emitting surges in excess of 500v), causing the unit to freeze. If the temperature gauge does not move past the cold mark, try power-cycling the unit by pulling and re-inserting the 12v inline fuse. If the unit remains unresponsive to a warm-up cycle under any circumstance, please reach out to our support team.