P2647 is a Honda-only trouble code. The VTEC system is one of the many Honda inventions and P2647 is a trouble code indicating a problem with the way the VTEC system is working. But before jumping into specifics, let’s go over some background information.
WHAT IS THE HONDA VTEC SYSTEM?
The VTEC system allows for an engine to have two separate camshaft profiles. One profile provides a smooth idle for better emissions and comfort. The other provides more power when the engine is revving faster. It’s the best of both worlds.
Honda vehicles with the VTEC system have two sets of cam lobes. One for low speed, the other for power. Hydraulicly controlled rocker arm pins engage the high-speed cam lobes.
This is controlled by a VTEC solenoid that routes pressurized oil to the rockers. To make sure the system is working properly, Honda adds a VTEC oil pressure switch to the oil passage to verify the valve is working when commanded.
What the Honda VTEC system isn’t
P2647 has nothing to do with variable valve timing on a Honda. Older Honda vehicles had VTEC only, but newer Honda cars also have VTC (valve timing control).
VTEC controls the cam profile. VTC controls the valve timing. The two acronyms are pretty similar. To make the confusion worse, Honda sometimes refers to the two systems together as i-VTEC.
Regardless, if your Honda has a P2647, don’t waste time checking the variable valve timing actuator / sprocket, or the control valve. It’s not related, other than both systems rely on oil pressure to operate.
Can low engine oil cause P2647 on a Honda?
Low motor oil frequently causes Honda VTEC codes, but it’s usually not the culprit with P2647. Why? It’s because P2647 sets when the VTEC is stuck on, and low engine oil causes the VTEC to not work at all.
However, don’t let my talk you out of checking your engine oil. Maintaining your engine oil level is the single most important thing you can do to take care of your Honda.
HONDA SERVICE BULLETIN FOR P2647
As I mentioned in the meta description, P2647 has a common cause on Honda cars – The VTEC oil pressure switch. Honda has issued a service bulletin 13-021. This covers both P2646 and P2647.
The service bulletin affects the following cars:
- Honda Accord 2003-2012
- Honda Civic Si 2002-2005
- Honda CR-V 2002-2009
- Honda CR-Z 2011
- Honda Element 2003-2011
- Honda Fit 2007-2011
- Honda Civic 2012-2013
What if the VTEC oil pressure switch doesn’t fix it?
Service bulletins, tech tips, Identifix, and talking to other mechanics are all fine. Someone handing out the answer is certainly easier than doing the work yourself.
However, if that’s all you ever do, you won’t get the necessary practice and you’ll find the only way to fix cars is to find someone to guide you. If you’re DIY guy or gal, that’s fine. If you’re doing this for a living, you’ll need to learn and practice constantly.
How to figure out a P2467 on your own
The first step is always to figure out how a system works. For that you’ll need to read the service information, which isn’t always easy to decipher. I’ll summarize.
First, if your Honda has VTC, ignore that system. It will just add complexity and it isn’t related to P2647. The only commonality is that they both are fed pressurized motor oil.
How the VTEC system works
The system is pretty simple. Pressurized oil is fed to the VTEC valve. When the ECM (engine computer) want to turn on the VTEC, it supplies power to the VTEC valve, which is grounded to the engine block.
When the valve is energized it opens a passage between pressurized oil provided by the oil pump to the passages leading to the rocker arm pins. The rocker arm pins lock now the high-speed profile is active.
In order to verify the system is working, the ECM monitors the VTEC oil pressure switch. The ECM expects to see pressure in the rocker arm passage when the VTEC is commanded on and no pressure when the VTEC isn’t commanded on.
What causes P2467
Your Honda will set a P2647 when there IS OIL PRESSURE on the rocker side of VTEC valve AND the VTEC command is OFF. This will occur at idle, so if you want to see if the problem is occurring right now, you don’t need to drive. Just start the car and let it idle for a wall.
There’s a separate code (P2646) for the inverse (NO OIL PRESSURE on the rocker arm side of the VTEC valve AND the VTEC is commanded ON.
What’s tricky about that?
Here’s the part that confuses some people. Many people assume that when the VTEC oil pressure switch is ON, there is pressure to the VTEC.
That’s not the case. It’s counterintuitive, but when the switch is on there’s no pressure. When it’s off, there is pressure.
Some scanners will have a code description of “Rocker Arm Oil Pressure Switch Circuit High Voltage” for P2647. This can also be a little confusing, while technically correct.
You see, at idle the switch should be ON. When the switch is “ON”, it’s closed. When the switch is closed, it’s grounding a voltage from the ECM.
The description is accurate. The switch is off at idle, indicating high oil pressure when there should be low oil pressure, and the voltage at the switch is the ECM reference voltage, since the switch isn’t pulling it to ground.
Normal conditions:
Idle = VTEC OFF = switch ON = pressure low
Driving w/RPM over 2500 RPM = VTEC ON = switch OFF = pressure high
Abnormal conditions:
Idle = VTEC OFF = switch OFF = pressure high (sets P2647 Honda DTC)
Driving w/RPM over 2500 RPM = VTEC ON = switch ON = pressure low (sets P2646 Honda DTC)
Honda V6 engines with bank 1 and bank 2
The diagnosis for a P2647 on a Honda Odyssey V6 is the same as the 4-cylinder models. Some Odysseys use VTEC to turn off the valve actuation for the rear bank cylinders for better fuel economy, but if this form of VTEC fails, a different OBD II trouble code is set.