Help - 15A EFI Fuse blows upon starting engine!

Welcome to PriusChat!!

Do you have any dash lights illuminated?

 

When I see a situation like that, I just roll up the sleeves. Your wiring diagram (on techinfo.toyota.com) will show you exactly what circuits are downstream of the 15A EFI fuse, and the locations of connections and junctions where those circuits branch off. With a multimeter and some patience, you can divide & conquer by disconnecting some of the downstream circuits and checking in isolation whether they show continuity to ground, or whether the remaining, still-connected circuits still blow the fuse.

It can be tedious, but you eventually find the fault. If it sounds like too much fussing for you, your friendly local auto electrical shop will be where they do that kind of thing all day.

-Chap

 

Don’t know why your messing with o2 sensors.

Efi fuse B+ has 2 main paths. One is hardwired one is controlled by relay EFI M.

The hardwired goes directly to pin6 of the engine control module. That’s main power to that module. That module is prob ok because if it was blown the engine would not start.

The relay PATH goes to VSV PURGE coil V1 and MAF M1 and AIR FUEL RATIO SENSOR A5.
The VSV IS A VACUUM EGR SOLENOID,

My first suspect is the Maf is shorted. Followed by the VSV.

 

A good tech would put a light bulb in place of the fuse hardwire out the relay and if the bulb on bright start disconnecting the components I listed tillthe light bulb goes dim. Find the short.

Good luck. Need to find a guy who knows what he’s doing,

 

yeah in ohmmeter one lead on ground one lead on pin 1 see what the impedance is. Then disconnect that maf
Connector and see what that impedance is on pin 1.

Pin 1 is fuse b+
Pin 5 is ground,

See which one is dead shorted to ground. The dead short is the ground pin.Pin1 is on the other end of the connector. Hopefully pin 1 is really low like 10 ohms
With the plug disconnected. A dc short is easy to find. Not many devices on that path.
Keep ohmeter on that pin and disconnect the plugs I mentioned till short goes away.

Most likely is a compromised wire catching chassis somewhere. Is this a salvage title car or does it show signs of rodent damage? Take the cabin air filter out from behind the glove box and look for mouse doo doo. If mouse sign in there your pretty screwed.

 

Yes if you unplug the MAF and it does not blow the fuse ffrom there on its pretty positive the maf is shorted. Btw never heard of the EFI
fuse blowing so usually that means its something caused by someone and not a component failure per say.

I can look in my engine compartment for you tonight for parts location but the parts diagram shows the VSV EGR solenoid in the front of the engine to the left of the valve cover.
The air fuel is shown just to the right of the valve cover over by the PCV valve proabaly plugged intop the intake. I can get you wire colors to look for so just unplug them one by one till the fuse stops blowing or measure the ohms at the MAF pin 1.

With the maf unplugged and you have one lead of your ohmmeter on pin 1 and the other test lead on chassis what impedance does it measure what ohms? Remember pin 5 is ground so will show zero ohms or a dead short so pin 1 is on the other end..

I bet its like 10 ohms. Monitor pin1 and unplug the components watching for the low ohms to go away.

Be aware the car engine may not start with the maf unplugged. Even if it does all it will do is chug chug chug. So dont start the car with the maf unplugged.

 

sorry meant to say if you unplug the maf and then the fuse does not blow the maf is shorted. You can measure with your ohm meter across pin1 and 5 of the maf itself. If shorted will be like really low ohms.
But never seen a shorted maf. When the maf is not working the car will likely not run and if it does it will sound really bad,
Hope it’s the maf that’s easy,

 

Wiring color

Maf—- pin1 wire is black 12 volt pin5 is ground brown wire
VSV ——Black is 12 volts red wire is VSV valve to engine ecm pin 14
AIR FUEL SENSOR-black wire pin2 is 12 volts pin1-3-4 yellow green red all go to engine em

Engine ECM is behind glove box in cabin. In metal can.

 

Don’t know what

Module b integration relay means

You said the short was on the efi relay path.

In the meantime stop blowing fuses that will cause subsequent damage in a Prius, it does not enjoy a dead short on its 12 volt buss and can eventually take out an ECM. The 12 volt path is not to trifled with in a Prius.

Find a 12 volt headlight bulb and clip it in series too whatever fuse is blowing if there’s a short on that fuse line it will light up bright and not damage anything.

 

Post a picture.