2004 PRIUS WONT START

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by brianFord, Jul 28, 2025 at 7:00 PM.

  1. brianFord

    brianFord New Member

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    Little back story. Last year during an unusually rainy spring I had the red triangle and brake warning light come on while driving. Kept driving normal until i parked it. Once park i could not get it to go into drive or reverse, only neutral and park. Pull the negative on battery, let it sit, hook back up and down the road i go. This happened several time during the rainy season. Once the we went into our normal texas dry spell the car was fine. Fast forward to present. Went to have new tires put on and on the way home i come to the turn off to my house. Im slowing down, assume the engine shuts off like noral as im coasting and when i turn onto my street and press the gas pedal engine does not come back on and red triangle and brake warning light comes on. Im a few 100 yards from home so i go the rest of the way on electric. get home, unhook battery , hook battery back up and nothing. Red triangle, brake warning light and no Ready mode and no engine start. scanner showed code for gas pedal malfunction. replaced it, still nothing. only other code is PAO94 for dc/dc converter performance. Ive checked all fuses, fusible link, verified my 2 year old axillary battery is good. No repair shops withing 100 miles of me. Any help would be greatly appreciated.
     
  2. bisco

    bisco cookie crumbler

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    did you mean P0A94? watch
     
  3. Brian1954

    Brian1954 Senior Member

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    What was the actual trouble code you saw, not the verbal description.

    What scanner are you using to read trouble codes?
     
  4. brianFord

    brianFord New Member

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    P0A94 (DC/DC Converter Performance) and P1121 (throttle/pedal position sensor/Performance problem/coolant flow control valve position sensor circuit stuck). I changed the pedal assembly, no change. Ive had the CE light on for 5 years due to the coolant flow control valve. Had a toyota mechanic tell me not to worry about changing that. The scanner was a local GM certified mechanic with his SnapOn scanner. It was probably only pulling codes on the "surface" and not ones deeper in the system.
     
  5. brianFord

    brianFord New Member

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    Yes P0A94 (DC/DC Converter Performance), sorry. No brake system codes tho.
     
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  6. Tombukt2

    Tombukt2 Senior Member

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    If DC to DC is fubar 12 v won't charge . So at ready you'd see like way less that 13 v etc the 12v going down . As it not charging . DC to DC is essentially you're alternator
     
  7. brianFord

    brianFord New Member

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    I checked voltage with power off and it was 12.7V. Hit the Power Button and voltage jumps to 14V, but no Ready light and no engine start. I even put a battery charger on it to bring it up to 13.1V, put a jump box on it at the distribution area and still nothing.
     
  8. bisco

    bisco cookie crumbler

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  9. brianFord

    brianFord New Member

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    bisco: 2 year old battery. I charged it up and took it in and had them load test it. They said it was good.
     
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  10. dolj

    dolj Senior Member

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    That's not surprising as P1121 has nothing to do with the throttle or pedal sensor. That is a catch-all fortune cookie phrase to cover that code in multiple cars and/or models. The part of that phrase that is applicable is "coolant flow control valve position sensor circuit stuck". The best advice is to look up Toyota Prius DTCs in the Toyota Prius repair manual.

    The P0A94 has several sub-code that would help in the diagnostic effort. If you can share which sub-code your car has here that would help.