Just recently, like about a month now, I've noticed a noise coming from the engine compartment when it's in electric mode. It sounds like an electric motor running, but in a varying fashion, up and down in pitch. (rrrRRRRRrrrrrrRRRRRRRrrrrrrrRRRRR). It is intermittent and I doubt it's the rad electric fan, as the other eve it was cool out and I had just popped out for a short errand run. Thus there's no way the engine was warm enough for the rad fan. Asked the service reps for ideas during a routine maintenance today and they had no clue.

 

Having n ow browsed a few posts, could it be the MECS pump?

 

Sounds like the MECS pump to me.

 

Try turning the HVAC system OFF and see if the motor stops running while in electric mode. If it does, it's your electric heater pump making the noise. If the noise is your MECS pump, it will run with just the key ON without starting the engine.

Remember, when the engine is OFF while in EV, the belt driven water pump stops. There is a electric water pump that comes ON in EV to circulate heated coolant to the HVAC heater core to continue heating the cabin. The only way to stop the heater pump from coming ON in EV is to turn the HVAC system in the OFF position. I keep my system OFF most of the time to save the HV battery for EV driving. The 12V battery and DC/DC converter uses less energy when the heater pump is OFF. The electric heater pump will last longer and you will improve your MPG. The electric heater pump runs in EV with the HVAC system is in any position but OFF. The smaller electric heater pump is located under the radiator like the MECS pump and they have been mistakenly replaced for each other in the past.

GaryG

 

I have a noise like that and believe it to be the MECS pump.