P2646 OBD II Trouble Code

Need information on the code P2646? You’ve come to the right place. In this blog post, we cover everything you … Continued

Need information on the code P2646? You’ve come to the right place. In this blog post, we cover everything you need to know about the “’A’ Rocker Arm Actuator System Performance / Stuck Off Bank 1” or P2646 code, including its meaning, potential causes, repairs and so much more.

Meaning and Cause of the P2646 Code

Because it starts with the P2xxx, the P2646 is a powertrain generic, or government-required code that applies to all vehicles with the OBD-II system. In other words,  all newer makes and models (1996 and newer). Although generic, the specific repair steps for this Diagnostic Trouble Code (DTC) vary from vehicle to vehicle.

What does the code P2646 mean? You’ve seen the code’s definition – “’A’ Rocker Arm Actuator System Performance or Stuck Off Bank 1” – but unless you’re a mechanic, it doesn’t tell you much, does it? Although it sounds awfully complicated, the actual meaning behind this code is far from difficult to understand. To put it bluntly, P2646 indicates that there is a problem with the ‘A’ rocker arm actuator system for Bank 1, meaning it either isn’t working properly or it’s stuck in the ‘Off’ position. The letter ‘A’ refers to the intake camshaft, while Bank 1 simply refers to the side of the engine that has the #1 cylinder.

Before we get into the possible causes of this DTC, we need to address the function of rocker arms and camshafts. A properly working cylinder lets the air in and out with the help of valves that open and close in relation to piston position. The valves ‘know’ when to open and when to close thanks to our vehicle parts of interest – rocker arms and camshafts. Here’s how that goes: using the timing belt, a part of the crank called crankshaft drives the camshafts; these in turn press down rocker arms, which in turn press those valves. By pressing them, valves let the air in and out of the cylinder.

Alright, so the meaning of the P2646 code should be at least a little clearer by now. But what causes it? The most common causes of this DTC have to do with oil problems and/or oil sludge, although this particular code can have a number of causes.  In any case, the most common ones are:

  • Low oil level
  • Oil pressure not up to specifications
  • Low quality oil/too thin or too thick oil
  • Clogged oil passages
  • The rocker arm actuator is clogged with sludge
  • Excessive sludge in the engine preventing the rockers from moving
  • The rocker arm actuator is sticking intermittently.

Springs of valves cylinder head

Symptoms of the P2646 Code

Although the causes of the P0646 code may vary from model to model of the vehicle, the symptoms are usually experienced in the same or at least very similar ways. The following symptoms are the most common ones across all makes and models:

  • Illuminated Check Engine Light
  • Reduced engine performance
  • Poor fuel economy
  • The engine valve not moving as it should, causing low power condition
  • Choppy acceleration
  • The engine valve train may be too noisy (this can happen if one or more rockers are stuck in the ‘Off’ position).

Diagnosing and Repairing the P2646 Code

Although the ‘A’ rocker arm actuator will usually be the problem (and will need to be replaced), this is not always the case. Often, the culprit will be the oil itself (low oil level, inadequate oil pressure or viscosity), but mechanics will replace components in error, causing the P0646 code to return. Misdiagnoses are costly and can actually cause further damage to the vehicle, so it’s crucial to avoid them. To do this, thoroughly inspect your vehicle, especially oil and oil pressure, as well as electrical components.

Your mechanic will diagnose the P2646 code by doing the following:

  • Mount the OBD-II scanner into the OBD-II port and record all stored codes and freeze frame data. Having freeze frame data is important as it can tell you in what condition the vehicle was in when the P2646 code turned up.
  • Start the inspection of the vehicle by checking the oil level and pressure. To properly function, the VTEC system needs adequate oil level and pressure, but if there is insufficient oil in the system, there cannot be enough pressure. If all is well there, check oil viscosity. Oil that is too thin cannot build enough pressure either, and as a result, the VTEC cannot operate properly. One of the ways this can happen is if the last oil change was performed in an incorrect manner. It’s also possible that there is fuel in the crankcase which can happen because of leaking injectors or even misfiring. Finally, check if there is any oil sludge. Irregualr oil changes can lead to residue and sludge, which in turn can clog oil passages and cause the VTEC system to stop operating. One of the ways to fix this is to perform an engine oil flush and switch to synthetic oil as this can clean out residue.
  • Check electrical connectors. Look for broken or bent pins, corrosion and other damages and repair or replace as needed. Also check wire harness for damage and repair if necessary.
  • Perform the manufacturer pinpoint test on the rocker arm actuator system.

Note: make sure you clear the code every time you perform/replace a component.

To conclude, the following repairs may fix the code P2646:

  • Replacing the ‘A’ rocker arm actuator
  • Changing the oil and filter to improve oil viscosity
  • Flushing the oil passages of sludge
  • Repairing the electrical connectors
  • Repairing the wiring harness.

Machanic repairman at automobile car engine repair

Additional Information About the Code P2646

This DTC doesn’t pose any serious danger to the driver but since it causes low power situation, it’s is a serious code that should be fixed as soon as possible. That being said, any code that lights up your Check Engine Light should be dealt with as quick as possible, so the P0646 code is no exception.

Another important thing to keep in mind is that the code P2646 is not very common. In fact, although generic, one could also say that this DTC has some of the properties of manufacturer-specific codes, because not all vehicles have engines with the rocker arms or actuators for the rocker arms. For this reason, you won’t see it in all vehicles, but those that do get it (Honda, Acura and others), will usually have a problem with the oil. This can happen due to irregular oil changes or if the oil used is of low quality (too thin or too thick). Another common offender is oil sludge as it blocks oil passages and stops the VTEC system from functioning properly. Whatever the cause though, it’s a good idea to let a professional check your vehicle as advanced tools are often necessary to deal with the P2646 code.

Code Explanations

These links will provide more detailed insights into what code means in your vehicle:

P0303 Code
P0456 Code
P0155 Code
P0430 Code
P0705 Code
P0741 Code
P0449 Code

Be sure to also read our essential guide to the best OBD2 Scanner.

Sources:

  1. P2646 OBD-II Trouble Code: ‘A’ Rocker Arm Actuator System Performance / Stuck Off Bank 1 – YourMechanic.com