P2646 Honda: Rocker Arm Oil Pressure Switch → Low Voltage

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P2646 is a common diagnostic trouble code that affects Honda made vehicles.  It indicates that there is an issue with rocker arm oil pressure switch.  The Rocker arm oil pressure switch verifies the correct oil pressure in the Variable Valve Timing (VVT) mechanism, and is often referred to as the VTEC (Variable Valve Timing & Lift Electronic Control) switch.

If you are getting P2646, one of the most common reasons that it pops up is the wrong weight oil was used during the last oil change.  So, if you’ve recently had an oil change, you may wish to start by replacing the oil with the proper oil recommended by Honda.

 

Honda P2646 Diagnosis
Typical VTEC Switch

 

P2646 Symptoms

Honda P2646 when it appears by itself does not usually correspond to any noticeable drivability symptoms.  You may notice a minor dip in performance and fuel mileage.  If the VTC strainer screen is clogged, the engine may die under heavy acceleration

 

Common P2646 Causes

The VTEC system controls the variable valve timing in your Honda.  It does this by activating the VTEC/Rocker arm solenoid.  It uses the Rocker Arm oil pressure switch to monitor the pressure of this system.  When the pressure is lower than the solenoid, the check engine light will come on and you’ll get P2646.

Here’s a great video on diagnosing P2646 from jimthecarguy on YouTube.

 

 

Here are the most common causes for P2646:

  • Wrong Oil– If you are unsure of the oil weight in your Honda or Acura, this would be a great place to start.  Even if you are sure of the oil weight, take a look at the dipstick.  Make sure that it doesn’t look milky.  If it does look milky, you could have some coolant leaking into the oil pan.  This would hurt the oil’s viscosity and trigger the P2646. 
  • Low Oil– If the dipstick is not registering oil at all, it may be too low for the VTEC system to function properly.
  • Wiring Issue– P2646 indicates that the voltage from the VTEC/Rocker oil pressure switch is low.  This means that a wiring issue very well could be at fault.  Take a look at the wiring harness where it plugs into this switch.  Make sure that it is undamaged and securely plugged in.  Trace the wiring back and see if it is damaged anywhere. 
  • Bad VTEC/Rocker Oil Pressure Switch– After looking at the oil and making sure that it’s ok, and checking the electrical connection, replacing the switch is the next thing to try.  On most Honda made vehicles they aren’t that hard to get to.  And, they aren’t that expensive.  There are many technical service bulletins on Honda made vehicles for this switch.

 

P2646 Conclusion

Good luck diagnosing P2646 in your Honda.  If there is anything that you would like ta add that could help someone else with this code, please leave a comment below.  Thank you.