Help - 15A EFI Fuse blows upon starting engine!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by minivaka, Mar 22, 2018.

  1. minivaka

    minivaka New Member

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    HI!

    I've been reading Priuschat a lot but I haven't found a solution to my specific problem yet.
    My 2004 Prius, the efi fuse blows everytime the engine is started. I read somewhere that the Module B in the relay box may be the cause (easy fix) so I replaced that but the problem persisted. When I unplug module B, the fuse doesn't blow but the engine wont stay on for long (I'm assuming that's because module B is unplugged).

    I read that some wires near the O2 sensor may have been damaged (due to burning when touching the exhaust or something). I checked the O2 sensor for cracks or dirt, but not the wires so I'll check that again.
     
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  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!

    Do you have any dash lights illuminated?
     
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  3. minivaka

    minivaka New Member

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    Yes. The lights shown are: big red triangle with exclamation mark in it, yellow circle with exclamation mark, vsc.
     
    #3 minivaka, Mar 22, 2018
    Last edited: Mar 22, 2018
  4. minivaka

    minivaka New Member

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    If it matters, this was first noticed while driving on a VERY hot day.
     
  5. minivaka

    minivaka New Member

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    I'm so sorry, it's actually a 2007 prius if that changes anything
     
  6. minivaka

    minivaka New Member

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    When I unplugged the downstream O2 sensor and unplugged the module B relay and turned the engine on I received these codes: P0ADF, P3000, P3190, P0A80, P0A84, B1421

    Then I rest all the codes

    When I unplugged the downstream O2 sesnsor and plugged in the module B relay and turned on the engine I saw these lights on the dash:
    Large red triangle with exclamation point, abs, vsc, circle with exclamation point.

    I used techstream to find codes and reset codes
     
  7. ChapmanF

    ChapmanF Senior Member

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    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
     
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  8. minivaka

    minivaka New Member

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    Thanks, Chap! I'll start the process. I'll post any updates if I have them.
     
  9. edthefox5

    edthefox5 Senior Member

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    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.
     
    #9 edthefox5, Mar 22, 2018
    Last edited: Mar 22, 2018
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  10. edthefox5

    edthefox5 Senior Member

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    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,
     
    #10 edthefox5, Mar 22, 2018
    Last edited: Mar 22, 2018
  11. minivaka

    minivaka New Member

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    By MAF M1 do you mean the mass air flow under/infront of the air intake filter? It has 5 prongs, is there a way to see if the connector is shorted or the MAF itself is shorted by using an ohmmeter?
     
  12. edthefox5

    edthefox5 Senior Member

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    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.
     
    #12 edthefox5, Mar 22, 2018
    Last edited: Mar 22, 2018
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  13. minivaka

    minivaka New Member

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    I'm the first owner of the car and it's never had rodent damage. I've actually replaced the cabin air filter while working on fixing this current issue and no rodent signs.

    If I unplug the MAF and the 15amp fuse still shorts, does that mean the MAF or its connector is not a culprit for this issue?

    I'm having trouble finding the location of the VSV on a 2007 prius. Why can't I find any links online for that?

    Is the air/fuel ratio sensor the same as the upstream O2 sensor?

    Thanks for all of the help, by the way!
     
  14. edthefox5

    edthefox5 Senior Member

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    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.
     
    #14 edthefox5, Mar 23, 2018
    Last edited: Mar 23, 2018
  15. edthefox5

    edthefox5 Senior Member

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    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,
     
  16. edthefox5

    edthefox5 Senior Member

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    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.
     
  17. minivaka

    minivaka New Member

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    Thanks for all the help! I'm going to do a lot of troubleshooting today and get back to you with results. In the meantime, could you tell me if this means anything:
    Everything plugged in, start engine, fuse blows.
    Only unplug module b integration relay, start engine, fuse does not blow and engine starts but chug chug.

    Also I unplugged the MAF and the fuse still blew.
     
  18. edthefox5

    edthefox5 Senior Member

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    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.
     
  19. minivaka

    minivaka New Member

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    It's the rectangular box in he fuse box directly to the left of the efi fuse. It doesn't have any fuses on it but cables in the back.
     
  20. edthefox5

    edthefox5 Senior Member

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    Post a picture.
     
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