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2010 toyota prius electrical problem. Wonder if AMD can

Customer Question
2010 toyota prius electrical...

2010 toyota prius electrical problem. Wonder if AMD can help. I read his on-line help for a guy with an Air mass flow indicator problem and was impressed with his help

Mechanic's Assistant: How long has this been an issue? How many miles are on the car?

165000 miles. Just had the intake manifold replaced by toyota dealer two weeks ago. No check engine light leaving the dealer. Car failed 4 days ago on a trip up into mountains and was towed to my house

Mechanic's Assistant: Are you fixing your Prius yourself? What have you tried so far?

Yes, I got it running again by blocking the EGR valve. I think this created a huge vacuum leak that stopped the motor. But now i have a hard ground on the load side the EFI fuse #2. I have disconnected a lot of the emmisions sensors/equipment. ground is still there blowing the fuse as soon and the car is started.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Ground is on load side of the fuse and is there whether the care is running or not. What the mechanic can help me with is what components does this fuse feed? So I can check them.

Submitted: 4 months ago.Category: Toyota
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Answered in 14 minutes by:
12/29/2017
Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
Boxer54
Boxer54, Toyota Technician
Category: Toyota
Satisfied Customers: 1,761
Experience: ASE Master tech with L1 certification, Toyota Master Diagnostic Technician
Verified
Thank you for trusting us with your questions. That fuse goes to several components.
Purge Valve
Mass Air Flow Sensor
Oxygen sensor heater (bank 1 sensor 2)
Air/fuel ratio sensor (bank 1 sensor1) EGR valve
Try disconnecting those one at a time and see when your short goes away. Be cautioned, there could be some normal continuity through the oxygen sensor and Air fuel ratio sensors if the key is on as the circuit is for the heater side of that circuit
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Customer reply replied 4 months ago
I disconnected the purge valve, mass air flow sensor and EGR valve. You have o2 bank one sensor 2. I think this is the post cat sensor. I disconnected it and still have the ground.
Is the air fuel ratio sensor the bank 1 sensor 1 O2 sensor in front of the cat? If not, where is this?
So, I have all these disconnected earlier today with the exception of the post cat O2 sensor and still have the hard ground on the load side of the fuse. I went further and check the connectors (on the fuse side, not device side) and found only one lead for each that was ground with the exception of the Air Mass flow meter. For this connector, pins 3 and 4 are hard ground. Is this OK since this 5 pin connector is also for the IAT device in the air mass flow meter?
Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
the air fuel ratio sensor is the pre cat sensor. Give me a minute to look up the wiring diagram for the MAF sensor.
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Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
Pin 3 (black wire) at MAF goes to the fuse you are having trouble with. Should have power with key on. Pin 5 (white wire) is a ground from the computer.
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Customer reply replied 4 months ago
I found a wiring diagram online. I disconnected the following connectors: Air mass flowmeter, pre and post cat O2 sensors, EGR valve, vacuum purge valve (under intake manifold, and charcoal canister pump module (at the rear of the gas tank). Still have a hard ground on the load side of the fuse. I disconnected the 8 wire connector in the fuse box that has the hot wire for all these components. Ground went away at the load side of the fuse but the pin that supplies all components on the wiring harness side showed ground. So I guess the ground is somewhere in the wiring harness since the ground is still there with all the components disconnected. If so, I'm screwed. Does your diagram show another component that might be causing the ground that I have not disconnected? The car is running fine now since I closed the EGR valve. It no longer is supplying the massive vacuum leak that shut the car down. Besides not being emissions compliant and gas mileage, will the car drive this way? I was thinking about running separate hot wires from the fuse box to each of the components and splicing into the connector. But, this appears to be a job. But it may be my only choice. I can't pay for toyota to install a new harness.
Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
The wiring diagram only shows those components. How are you testing for the short to ground? What equipment are you using?
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Customer reply replied 4 months ago
volt/ohm meter set on ohms X 1. Black attached to the ground wires on the head near the oil filler cap. Remember, this started out with a blown fuse. I replaced and it immediately blew again when the car was started. I find the wiring harness has failed hard to believe. Tracing the wires back as far as I can see, there isn't any chaffing and the wires look good. Of coarse, I can't see under the shielding or under the fuse box. This is my sign's car and he is out of town. He said it just quit going into the mountains. I'll see if he can give some more info on what happened. What do you think of my last question on letting him drive the car to school and back (10 miles round trip)?
Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
With the EGR closed, and the car running, you should be ok to drive. Just have that check engine light. Checking for a short to ground using an ohm meter can be very misleading because literally ANYTHING can back feed across those wires and show on an ohm meter as continuity, even across a load. So, the BEST way to test is actually using a light bulb. I use a standard 1157 light bulb and socket salvaged from a broken taillight assembly. What you will want to do is remove the fuse and install the light bulb in its place. When the circuit is energized, and a short to ground is present, the bulb will light up brightly. When the short yo ground is removed, the bulb will go out or dim to an almost insignificant amount. Try checking it using this method and see if any one of the components we talked about are causing a short to ground. Be careful NOT to use any LED bulbs as this test won't work properly using them.
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Customer reply replied 4 months ago
sorry Boxer, I don't see how using a bulb changes anything. I have all the components disconnected. They are not in the circuit any more. So i am checking the fuse supply to each of the components on the wiring harness side of the connector and they ALL show hard ground for the fuse supply to the component with all the components disconnected at the same time. A bad component may have caused a fault in the harness but that doesn't solve the problem that I have a bad wiring harness somewhere.
Toyota Mechanic: Boxer54, Toyota Technician replied 4 months ago
The bulb actually determines there there is an actual short to ground and is the proper way to test it. Using an ohm meter is not the correct method. The tool companies sell short finders for a lot of money, and basically the tool is as I described to you using a bulb.
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