What Does The P2646 Code Mean In A Honda?


Not all trouble codes are made for every vehicle manufacturer. Some are specific to a particular lineup, just like the P2646 Honda code. Because this code is so rare, you may not know what it means and it can be difficult to find accurate information online. 

In this guide, we look closer at the definition of this trouble code and show you what symptoms you can expect. We also look at the causes, so you can figure out the right fix. Hopefully, with all of this information, you’ll be able to get your Honda back on the road. 

Code P2646 Honda Definition

P2646 – Rocker Arm Oil Pressure Switch Circuit Low Voltage or VTEC Oil Pressure Switch Circuit Low Voltage

What Does the Honda P2646 Code Mean?

The P2646 DTC means that there’s a voltage discrepancy between the rocker arm oil pressure switch (VTEC oil pressure switch) and the hydraulic circuit, determined by the ECM/PCM command. Once these parameters are different, the computer sets the code and the Check Engine Light comes on.

Honda uses a Variable Valve Timing and Lift Electronic Control (VTEC) system that’s unique to these and Acura vehicles. This system is responsible for activating the Rocker Arm Oil Control Solenoid, otherwise known as the VTEC Solenoid Valve. It’s commanded by the Engine Control Module (ECM) or the Powertrain Control Module (PCM). Its purpose is to charge the hydraulic circuit of the VTEC mechanism responsible for altering the valve timing from Low to High.

What Are The Symptoms Of P2646?

You can count on the Check Engine Light to come on the dashboard when the P2646 code is set. Aside from that, there can be some serious consequences to this trouble code. 

Here are a few to consider:

  • Check Engine Light
  • Stuck valve train
  • Engine performance issues
  • Noisy valve train, especially if a rocker gets stuck
honda vtec

What Are The Causes of the P2646 Honda Code?

In some cases, the reasons for the P2646 code are simple and won’t be difficult to diagnose. However, that doesn’t negate the fact that there could be some serious causes requiring more work to repair.

Here are some of the most common Honda P2646 causes.

  • Wrong motor oil viscosity
  • Clogged oil passages
  • Sludge clogs rocker arm actuator
  • Clogged oil control screener
  • Malfunctioning VTEC oil pressure switch
  • ECM malfunction

How Serious is the P2646 Code?

Severe – You don’t want to continue driving with the P2646 Honda trouble code. Once you realize this is the problem, it’s imperative that you get to a safe location and stop driving until repairs are made.

With the wrong oil in the system, permanent engine damage can occur. Additionally, if there is sludge or a blockage in the passages, the engine could fail to work at any time. 

How Do I Fix the P2646 Code?

You can’t determine how to fix this Honda trouble code until you perform complete diagnostics. We outline that information below, based on what we would do as professional mechanics. 

Until then, here are the most common fixes.

  • Oil change with the correct viscosity
  • Flush oil passages
  • Replace the rocker arm actuator
  • Clean rockers
  • Replace the VTEC oil pressure switch
  • Update/Replace ECM 
car head parts

Common P2646 Diagnosis Mistakes

Many mechanics want to rush right to the more complicated issues while overlooking the engine oil. In most cases, all that’s needed is an engine oil and filter change. Make sure you perform the change with the right viscosity. 

Additionally, technicians fail to check the factory service bulletins for this problem. It’s especially important if you have one of these models. 

  • 2003-2012 Accord
  • 2002-2005 Civic Si
  • 2002-2009 CR-V
  • 2011 CR-Z
  • 2003-2011 Element
  • 2007-2011 Fit

All of these models have bulletins telling technicians to replace the VTEC oil pressure switch. The part number for this replacement is 37250-PNE-G01 or H/C 6737217.

How to Diagnose the P2646 Honda Trouble Code?

If you want to diagnose this trouble code like us, you should follow the same guidelines we do. As a novice, you may prefer to read the factory service manual before getting started. This is a wise decision. 

After that, follow these steps. 

  1. Scan the engine codes. 
  2. Reset the codes and start the engine once again.
  3. Once the Check Engine Light comes back on, reread the newest codes. 
  4. View freeze frame data.
  5. Check the trouble codes with our DTC library for more assistance. If multiple codes exist, fix the others first, as this may inadvertently repair your problem. 
  6. Perform an oil change, ensuring you have the right engine oil viscosity. Remember to also install a new engine oil filter. 
  7. Use the manufacturer’s procedures for a pinpoint test on the rocker arm actuator system. 

Beyond these steps, you are getting into advanced territory. Unless you have knowledge about cleaning out the valvetrain, it’s best to leave these steps to the professionals. Contact a local auto repair shop that specializes in VTEC engines for more support. 

How Much Does It Cost To Fix Code P2646?

The great news about P2646 is that something as simple as an oil change can repair your problem. This is one of the cheapest solutions available. However, there are also some costly options you may need to consider.

On average, this is what you might spend on parts and labor. 

  • Oil and filter change – $50-$175
  • Flush oil passages – $50-$450
  • Replace rocker arm actuator – $85-$650
  • Clean rockers – $75-$425
  • Replace VTEC oil pressure switch – $65-$225
  • Update/Replace ECM – $250-$2,500

A Mechanic’s Tips About The P2646 Code

The Honda P2646 trouble code can in many cases, be completely avoided. With a normal oil change while using the right viscosity, the engine won’t get sludge buildup inside. Since this is the most common cause of the P2646 DTC, you won’t need to worry about it if you follow the recommended maintenance schedule

Keep in mind that the P2646 code isn’t common, except with Honda vehicles. The majority of vehicles don’t contain actuators for the rocker arms. Only engines with variable rockers are going to throw this code. 

Is code P2646 serious?

Yes, you don’t want to drive with the P2646 Honda trouble code. By using the wrong oil viscosity, permanent engine damage can occur. Plus, if any sludge has built up or there’s a blockage in the passages, the engine could fail to work at any time. 

How do I fix error code P2646?

In most cases, simply performing an oil and filter change can resolve the problem. It’s possible that there’s some sludge buildup or you are using the wrong oil. Otherwise, the fixes can be complicated and may require the help of a professional auto mechanic. 

What does the rocker arm actuator do?

The rocker arm actuator works as an oil pressure switch responsible for controlling the flow of oil to the cylinder head. It’s not included in every type of vehicle but common in the Honda VTEC engines. 

What is the VTEC oil pressure switch?

The variable valve timing oil pressure switch is located with the VVT solenoid and it tends to remain as an open switch. If it closes, the voltage drops to zero, telling the PCM that the oil pressure has been applied to the system. If the switch isn’t working, an engine code will be set, often P2646. 

Working with a Honda VTEC engine is never an easy task. Even as certified mechanics, we aren’t often thrilled to work on them. That’s why there are special Honda technicians available that have the expertise needed to figure out these advanced problems. 

Thankfully, you may only need to perform an oil change with the P2646 code. Even if you don’t want to do the advanced repairs, you can probably handle this maintenance job without much stress. At worst, you can take it to the local lube shop for a minimal amount of money. 

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Categories: OBD Codes

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