Does the Gen 2 Prius inverter cooling pump run continuously?

I recently received a P0A93 and VSC code. I noticed a sudden loos of power, likely the vsc. I was close to home, so just continued. The car appeared to run fine. I cleared the codes using a scanner and they have not returned, although I have only taken short trips. I followed several posts that indicate the inverter pump should run continuously whenever the ignition is on; however, I have also found a Haynes repair manual that says the pump only runs based on the computer demand. Several posts and other YouTube posts say to check the pump is running by checking the tank for a swirling. The only requirement is to place the ignition in the On position, or in ready, the system does not need to be hot. I performed this check and no swirl or pump vibration was evident.

I have checked the pump by using a jumper from a 12 volt battery and the pump runs fine and the swirl is evident when the pump is running. I used my OBDII scanner and monitored the MG1 and MG2 temps and they were relatively stable at 140 degrees average with rapid spikes to 160 quickly returning to 140 when under load. This was a test drive that started with the engine cold, it was about 55 degrees F outside temp. When I return home I checked the tank and the coolant had no swirl and the coolant remained cool, no temperature rise. This could be normal if the pump only runs when computer determines cooling is needed or it could be a problem if the pump should be running continuously. The error codes have not returned; but I am not confident about taking the car for a more challenging drive. Any insight or recommended reference material that defines the inverter pump operation? Thanks.

 

I removed the headlight since I was expecting to need to replace the pump; the posts all indicate that the pump is the most likely cause. Before removing the pump I connected the pump with a jumper to a spare 12 volt battery and to my surprise the pump ran, i could feel the slight vibration and also could see the coolant movement.

 

It appears the inverter pump relay is in the fuse box connector block under the drives side dash. I have been told this is in the “inner circuit” that is part of the body ecu and this type of failure is rare. The car does have 246K miles, so maybe first time failures can be expected. I did the simple check and removed the connector and did a continuity check, the connector is good and spiced it back.

 

I went to the library and used the ALLDATA repair reference material, it has circuit diagrams and troubleshooting. This manual troubleshooting chart shows the inverter pump is continuous, not intermittent. This ALLDATA manual shows the pump control is through the Hybrid Vehicle Control ECU. First thing is to check the relay if I can find it; but I if it is the inner circuit, I may need to replace the block. This seems unlikely, I think I agree it may be more likely a wiring issue as you indicate. Could this be a hybrid control ECU issue, seems unlikely that an ECU would fail for just this one function. wow this is getting complicated.

 

Locating the wiring issue is going to be difficult, the pump wire goes into the fuse box harness under the hood. Note: the pump white / black strip is ground!. Probably need a more advanced tester that can check circuits, not looking to spend a lot of money with a dealer. This is high mileage car and just looking to keep it running a bit longer. I am considering wiring the inverter pump in parallel to the front fog light 15amp circuit. The circuit should have a bit margin to handle the inverter pump which appears to only draw about 1 amp, appears that is an efficient little pump! I would just run with the lights on all the time. Looking for another alternate wire connection that is linked to the inanition on circuit?

 

I cannot see the harness connections without disassembly at the fuse box under the hood. The connector to the pump was in good condition. When I removed the connector, the pump pins were clean. The wire to the pump goes into a bundle and I cannot trace it without a lot of disassembly that would likely damage wiring in the process. In general, the fuse box terminals show no obvious corrosion.

 

I have found the inverter cooling pump relay terminals and confirmed the relay solenoid is functional and the contacts close when IG-ON. I checked the voltage going into the relay and out and discovered the voltage is only 6 volts into the relay. I checked the nearby accessary relay terminal, and it was 12 volts. I think this confirms the wire is intact but has high resistance causing a voltage drop between the AM2 fuse connection 31 to the inverter pump relay. This relay is part of inner circuit fuse block and does not appear to be something that can be replaced without changing the fuse block. The fuse terminals don't appear to have corrosion. I noticed the AM2 is in a fuse block that appears to be removable. Has anyone needed to replace this fuse block? I see it is available through ebay.

 

I measured the voltage at pin 10, 6 volts with ig off. With ignition on the pin 10 volts is 6 and pin 11 out is 6 volts. When ig off the pin 11 is 0 volts, I concluded the relay solenoid is working and the relay is good. I measured the voltage at the AM2 fuse, removed the fuse and measured to ground, 12 volts. I don’t know where to find 31 pin 1?