Dashboard illuminated with too many warning lights

The Prius has two integration relays. They are labeled B and C within the main relay/fuse box next to the inverter.

An integration relay is just a fancy name for four relays that are housed in one rectangular housing.

It does sound like a relay is not working since the problem is intermittent.

The troubleshooting process is basically to pick a circuit that is having a problem, and trace from the battery to the circuit. For example, if the overhead cabin lights do not work, that is an important clue because that circuit also keeps alive various ECU memories.

Consult the electrical wiring diagram (techinfo.toyota.com) to see all components between the 12V battery and the dome light. Look for the relays in the circuit path, since the problem is intermittent. When the light is not working, hit each relay with a screwdriver handle to see if the mechanical shock will encourage the relay to engage. Hopefully you can find the failing relay that way.

Another way to test the relays is to remove each one that is suspect. Look at the relay socket contacts and the relay pins that mate with the socket, and clear any corrosion using electrical contact cleaner spray. Apply 12VDC to the relay coil terminals (use an ohmmeter to figure out which are the coil terminals and which are the switched terminals. The coil terminals will measure ~100 ohms resistance.) Then measure resistance across the switched terminals. If the resistance is not 0.5 ohm or less (after accounting for test lead resistance), replace the relay.

 

Is OK as-is.

 

Well, the electrical wiring diagram shows that there are three wiring harness connectors that mate with the three connector sockets on the B relay.

 

At this point, what problems remain with your car?

 

Also, were you able to try the diagnostic test that Patrick suggested?
what were the results?

- Apply 12VDC to the relay coil terminals (use an ohmmeter to figure out which are the coil terminals and which are the switched terminals. The coil terminals will measure ~100 ohms resistance.)
-Then measure resistance across the switched terminals.
-If the resistance is not 0.5 ohm or less (after accounting for test lead resistance), replace the relay.​

 

According to the electrical wiring diagram, Unit B has the four fuses on top. It has three wiring harness connectors. Unit C has no fuses and only has two wiring harness connectors.

Also, Unit B is supposed to be closest to the driver's side fender.

Let's focus on the power windows for a moment. Use your digital multimeter set to measure voltage. Make sure you have 12VDC at the following fuses when the Prius is READY: 15A DOME, 7.5A ACC, 7.5A ECU-IG, 30A PWR, 10A GAUGE, and 20A FR DOOR. (Pull one fuse at a time and make sure you can measure 12V to body ground, from one of the fuse terminals. Measure resistance across the fuse to make sure each fuse has continuity.)

If any of those fuses do not have 12VDC, record which ones have a problem and post.

 

The car should be IG-ON or READY when you are measuring voltage at the fuse box. When you are measuring continuity of the fuse it doesn't matter what the state of the car is since the fuse is removed from its socket.

Depending upon the fuse that you pull, the car may drop out of READY state into IG-ON state.

 

Deleted since I not remember if info was correct.

 

Ambrosia,
My customer had similar issues.
After some troubleshooting I determined that the receptacle for the 15 amp fuse for the dome light was bad.
The fuse itself was fine.
I could put my finger on the fuse, and wiggle it back and forth while watching the dome light.
Customer had been living with the problem for 3 years.
Randomly the dome light, clock, door locks, audio beeps, would stop working.
Car fob would start the car only when in the ignition slot.
But he never had a situation where the car would shut itself off.

 

You don't have to test every fuse, just the ones Patrick noted. And did you do the test for 12V at the fuse contacts in the fuse block? That's just as important. Checking those contacts should also show loose contacts as mentioned above.

You should not be testing HV circuitry right now.

You measured the internal resistance of the oscillator's circuitry.