I just went to check my son's Avalon (we have 5 in the family). I checked his relay voltages which are as they should be term 5 12.07v, 1, 2, &3 are 0v.
The above is correct for a battery connected, no key in ignition situation.
Terminal1 is 10.9v,
2 is 0v,
5 is 11.94v,
3 is 2.28v
The above is not correct for a properly operating system.
With the EFI Relay removed, battery connected, key out of the ignition (key in OFF position), you should get these values:
- Terminal 5: 12.6 VDC
- Terminal 3: 0 VDC
- Terminal 1: 0 VDC
- Terminal 2: 0 VDC
So your son's Avalon is good. Your own Avalon is not (plus your battery is weak/undercharged). The 10.9 VDC on terminal 1 is very low, likely causing very low magnetic output from the coil side of the relay, and causing the contacts to open/close rapidly. It is not necessarily the fault of the ECU though (but it certainly could be). There could be a problem where a live power wire "B-W" (or black insulated wire with white stripe) is contacting the "L-O" wire (or blue insulated wire with orange stripe) within the wiring harness somewhere. A good way to figure this out would be to disconnect the "E" wiring harness connector (a 22-pin wiring harness connector) at the ECU and then check the voltage on all 4 EFI Relay socket terminals again. If the problem with voltage on terminal 1 remains, the ECU is not at fault - there has to be a wiring harness defect causing a live wire to be in contact with the "L-O" wire feeding EFI Relay socket terminal 1. If the voltage on terminal 1 goes to zero with the "E" wiring harness connector removed from the ECU, then the issue is within the ECU.
So a little more diagnostic testing and you should be able to narrow down the source of the power problem.