*310,000 Miles* Something w/Ignition system not working

Discussion in 'Gen 2 Prius Technical Discussion' started by AlaskaLad, Aug 22, 2020.

  1. AlaskaLad

    AlaskaLad New Member

    Aug 22, 2020
    Juneau, AK
    2004 Prius
    Hello...first off I've had my prius for 6 years and have only had 1 previous problem which was changing out the ignition coils and spark plugs 4 years ago which fixed it. Until now Ive been extremely lucky and its reached 310,000 miles without major mechanical issues (odometer stopped at 299,999 and I keep track with the trip logs).

    Currently the car will start, have a rough shake and then the engine will fail and all the lights on the dash come on. It will not allow me to go out of park or neutral. Before this the car would shake when starting and then shake when accelerating which I'm familiar with because that is what happened when I had to change the coils the first time. Side-note I live in a rainforest and this happened on both EXTREMELY rainy summers 4 years apart. So I got home parked it and changed out the coils and plugs once they arrived, all of them. I ordered online because parts where I live in Alaska are stupid expensive, I tested the coils and they were all functioning fine. Once I replaced everything the car started perfectly, I drove about 6 miles roundtrip but when I parked it turned it off and started it again it now shakes and then the engine fails within seconds. I re-checked all the plugs and coils and they are working, a friend read the codes and it just said ignition coils but didnt specify which (dont remember code, sorry). Weirder is that 10 days later when I decided to re-arrange the coils again it did the same thing where it started perfectly and then i drove it around once and when parking it stalled again and then when I turned it back on its back to stalling right after a few seconds. So when the ingnition coils do get the power they need the car works perfectly but only once and then not again so Im thinking a bad ignition relay?

    The ignition relay, which I cant seem to locate anywhere on the internet as to where that is on the 2004 prius. My thinking is because it is acting the same way that it does if I were to unplug the coils while its running, the engine stalls but the electrical components remain on. Somehow electricity isnt getting to the coils or not enough power is getting there.

    Ive checked battery voltage and its fine, 12V battery was just replaced less than 6 months ago.

    Has anyone else had this or can offer any advice before I give up and have it towed to a mechanic here.

    Before anyone comments, No Alaska isnt always dark and cold and yes it does have a rainforest...the largest temperate one in the world.
    edthefox5 likes this.
  2. ydpplqbd

    ydpplqbd Active Member

    Aug 1, 2019
    2006 Prius
    Start with basics:

    1.) Next time CEL (CEL turns on when DTC(s) arise) comes on, review DTC codes and WRITE THEM DOWN in a dedicated notebook. Only after documenting DTCs should you reset CEL .

    2.) Do you have spark on each coil (IOW take off coil pack one and place a known good spark plug into coil pack (while pack is sitting on top of valve cover and check whether you have good spark)?

    3.) Do you have any grounds that are unconnected, crapped-out, green and crusty, etc.?

    4.) What is the voltage at each coil pack?

    5.) Do a voltage drop test from known under hood known excellent ground (such as strut tower bolt) to each of the coil packs.

    6.) Let us know the results of your testing. ignition_2004_2006_coil wiring.JPG

    PS I have a ttached a schematic from a Prius Gen2 repair manual showing coils (and injectors) attached to ECM (through the required harness. See pic.