Help - 15A EFI Fuse blows upon starting engine!

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

  1. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,045
    6,016
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    The B integration relay contains four relays in one assembly. When you look in the main relay/fuse box next to the inverter, you will see two integration relays, one marked B and the other marked C. The B relay has four fuses in it while the C does not have any fuses.

    The 15A EFI fuse provides power to the engine ECU and the mass air flow sensor via the EFI M relay which is part of integration relay B, and the fuel pump via the C/OPN relay, which is part of integration relay C.

    As Ed suggested, stop stressing the circuit by repeatedly installing a new fuse when you know you have a short. Instead, rig up a little 12V light across a burnt out fuse's pins (for example, a W5W or Sylvania 2825 side marker light bulb) and plug that assembly into the EFI fuse socket. The light will remain on as long as power is applied to the circuit and a short persists.

    Then work on figuring out whether the problem is with the wiring to the mass air flow sensor, or to the engine ECU, or the wiring to the fuel pump, or maybe the MAF sensor or the fuel pump itself is shorted.

    Also, you should put a charger across the 12V battery as it is getting drained with all of this testing going on.
     
    #21 Patrick Wong, Mar 24, 2018
    Last edited: Mar 24, 2018
    Andyprius1 likes this.
  2. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    7,449
    3,165
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    That’s what I thought he’s killing all b+ downstream by disconnecting the module so the efi relay is now dry so yeah no more blown fuses now lol.....
     
  3. minivaka

    minivaka New Member

    Joined:
    Dec 18, 2017
    12
    2
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Yea, sorry. Here's that. There is a red circle around the efi fuse and a blue circle around the B module
     

    Attached Files:

    Raytheeagle likes this.
  4. minivaka

    minivaka New Member

    Joined:
    Dec 18, 2017
    12
    2
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    I've just set up a lightbulb to the fuse and will work from there. The fuses are on my C integration relay, not B. I posted a photo. Before I hooked up the bulb I tried one more time with the MAF, A/F sensor, and the VSV, and the fuse still blew. I will not be doing any more tests without the bulb rig.
    I think the issue is either the engine ecu or the hybrid battery ecu (because I did replace a battery module in the hybrid battery and may have messed up the wiring or damaged a wire). It's just difficult to actually troubleshoot all of the wiring. I was able to locate the engine ecu and just by visual inspection the wiring seems fine but I'll have to go at it with an ohmmeter, just unsure exactly how. I might want to get someone more experienced and knowledgeable to look at this but the car can't move anywhere. I'll post here with updates. Thanks for the help!
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,045
    6,016
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Yes, you are right. I just looked at my 2007 and the fuses are on the C integration relay. My electrical wiring diagram is for the 2006 model year so it may have errors in it. For example it labeled the B relay as located in the C position and vice versa.

    If you are going to continue to troubleshoot this yourself you may want to obtain the electrical wiring diagram for 2007 as it may help you to see exactly what circuits are powered by that fuse, so that you have a chance to find where the short is. techinfo.toyota.com

    Good luck.
     
    Andyprius1 likes this.
  6. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    7,449
    3,165
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    Engine control module is not shorted because it is hardwired to the efi fuse and if shorted would continuously blow that fuse just sitting there with the engine off.


    If I was there I would replace the fuse. I would pull the efi relay.on the relay itself is a pin diagram of its connectors. 2 pins are control coil. Other 2 pins are the relay contacts. With your headlight bulb fuse jumper light jump across those contact pins. If that circuit shorted light will be on bright.

    Jumping out the relay with load light allows you to work on it.
    Pull the maf and VSV solenoid and purge valve plugs and if light still bright you have a wiring short.

    You can also use an ohmeter instead of the light bulb. Not sure of your level of electronics. First thing I woul like to see is what is the impedance of the rail after the relay contact. Is it a dead short?


    Using ohmeter With car off in ohms what does pin1 of the maf measure to ground? I’m just measuring that rail impedance nothing to with maf. Disconnect maf connector and measure pin1 to ground.

    Btw I have a 2007 electrical wiring diagram. So I know it’s correct.
     
  7. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    7,449
    3,165
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    I do see something odd in this circuit though. This is confusing.

    There’s 2 relays is the area of interest. The one that’s labeled EFI
    provides power to the maf and VSV and the airfuel.
    But EFI means electronic fuel injection.

    The relay next to it in my book is labeled IG2. That relay only goes one place the fuel injectors. So why is that relay labeled IG2 and not EFI.

    The fuses are labeled the same as the relays.
     
  8. Mrs.Diamond

    Mrs.Diamond Junior Member

    Joined:
    Feb 20, 2018
    44
    8
    0
    Location:
    Minneapolis, MN
    Vehicle:
    2009 Prius
    Model:
    Three
    Removing my post as it got posted in the wrong threaf
     
  9. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    7,786
    5,434
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    There are no wrong threafs.

    Ed, you've discovered something I also like to repeat from time to time ... the short labels on the fuse boxes are really not enough to diagnose with. Sort of like the fortune cookies for the trouble codes, they are kind of broad hints at what the engineers might have been thinking about when laying out that circuit, but other stuff gets included on the same circuits for various reasons, and so on. To be fair, they are probably about as accurate as the scribbles on the door of most people's breaker panels at home.

    When you're working on a problem that really requires knowing where the juice comes from and goes to through each fuse ... wiring diagram.

    -Chap
     
    Mrs.Diamond likes this.
  10. Erik Owens

    Erik Owens Member

    Joined:
    Mar 25, 2018
    162
    55
    0
    Location:
    Florida
    Vehicle:
    2010 Prius
    Model:
    Three
    Classic short to ground you sillies.
     
  11. TMR-JWAP

    TMR-JWAP Senior Member

    Joined:
    Aug 12, 2016
    2,425
    2,882
    0
    Location:
    Columbia, SC
    Vehicle:
    2007 Prius
    Model:
    Touring
    The EFI fuse is the power source for:

    Pin 6 of the ECM


    And via the EFI M relay:
    Canister Pump Module Vent Valve
    VSV (fuel Vapor Containment Valve)
    Pin 4 of the ECM
    MAF Meter
    Heated Oxygen Sensor Bank 1 Sensor 2
    Fuel Pump

    The Oxygen sensor is the one after the cat converter, on the horizontal piping.
    The air-fuel ratio sensor (bank 1 sensor 1) is located on the exhaust manifold just before the first flange where the exhaust manifold bolts to the exhaust piping.

    The connector for the O2 sensor is under the carpet on the passenger side. Kind of where that persons left ankle/calf would be.
     
    #31 TMR-JWAP, Mar 28, 2018
    Last edited: Mar 28, 2018
  12. Erik Owens

    Erik Owens Member

    Joined:
    Mar 25, 2018
    162
    55
    0
    Location:
    Florida
    Vehicle:
    2010 Prius
    Model:
    Three
    Shorted to the 5 Volt reference. I would start with disconnecting every one of those except the ECM until the lights goes out on your jumper or untilt fuses stop popping. Wasnt that easy?
     
  13. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    7,786
    5,434
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    It's especially easy if you've got somebody like TMR to look up the necessary information for you.

    -Chap
     
  14. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    7,449
    3,165
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    TMR your right my bad. In my haste to help this guy I looked at my print too quickly and missed junction block eb1 I just followed the line from the relay in and out of that block. It goes to everything you posted.
    May have Fod damage on the o2 wiring under the car and caught a short. Lots of b+ connections to the ECM and that may be shorted but he said the car started also hardware b+ to pin6.
    So can’t see how the car started with shorted ECM unless it’s not starting just spinning.

    Been trying to get this guy to hang an ohmeter on this path like I suggested in post #12 but he may not understand that. Pretty easy and fast pin1 of the maf is on this b+ Rail. Measure that to ground start unplugging.
    I have the factory manual.
     
Loading...