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2010 Prius EC P0A4A, P07E8, and more. Help Diagnose

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Prius-gang07, Jan 9, 2023.

  1. Prius-gang07

    Prius-gang07 New Member

    Jan 9, 2023
    2007 Prius
    I got a 2010 Base Prius and have had a rough couple of months with it. Now it turns on, but won't move.

    Around 8 months ago I had Engine Codes P0420 and P0403. It idled pretty rough, but not too bad. I cleaned up and got the EGR Cooler looking brand new. I did not clean the EGR Pipe or the Intake Manifold as I've now seen in some recent videos.

    Definitely helped and had the car running well a few weeks, but then I had some rough and loud idles, this time it sounded like a helicopter.

    Took it to a shop and got the Exhaust Manifold Gasket and Catalytic-Manifold Donut Gasket replaced. Seemed to do the job, but they found a chunk of my Catalyst broken off inside.

    Had the car running well for a few more weeks when I started getting some rough idles again, but it didn't sound like an exhaust leak this time. This happened after some really rainy days. Had the Check Engine Light on so I scanned and pulled many codes (cheap Walmart scanner):
    P0300, P0301, P0302
    P0101, P0171
    P0A4A, and P07E8 (NOT $7E8)

    I cleared them thinking it could've been a short circuit considering the heavy rain, but the last four codes remained. Took it back to the shop, and they found a hole on the Intake Manifold on the runner for cylinder 2 in it's EGR passage. Looks like it had burned/melted through. That explained the P01XX codes.

    They told me to bring it back when the new manifold came in, but on the way home I barely topped of at 25MPH when it stopped accelerating. No engine sound, no eCVT sound, just coasting, so I pull to the side of the road.

    Check Hybrid System warning came on, and the car would no longer enter any gears (D,R, or B) except for Neutral. Turned it on and off a couple times, but to no avail. Had the car towed home and the P07E8 and P0A4A codes were there.

    Only information I could find was for P0A4A which mentioned a position sensor for Motor B
    repairpal com/obd-ii-code-p0a4a-drive-motor-b-position-sensor-circuit-overspeed

    I also saw a few videos showing how to "Reset/Clear" the CHS warning by disconnecting the Auxiliary Battery and a White Cable in the Engine Bay Fuse Box for about 10 minutes. Will try tomorrow, but unsure if it will really resolve anything.

    Please Help. I know its a long read, but I'm trying to be clear as can be.
  2. tankyuong

    tankyuong Senior Member

    Nov 9, 2012
    Central MO
    2012 Prius c
    blown head gasket
  3. ChapmanF

    ChapmanF Senior Member

    Mar 30, 2008
    Indiana, USA
    2010 Prius
    I don't see any smoking gun for the head gasket here. I'd be very interested in a photo of the melted manifold though.

    I'm questioning the codes reported by the cheap Walmart scanner. A 2010 Prius repair manual (at least the old edition I'm looking in right now) doesn't have any P07E8 code, in fact no P07xx codes at all.

    It does have a few P0A4x codes. It can give P0A4B, P0A4C, or P0A4D. Those all have to do with the resolver circuit for MG1. (The resolver circuit for MG2 can also give three codes, P0A3F, P0A40, or P0A41.)

    Those three codes detect (in order): an interphase short in that resolver circuit, a signal from that resolver out of range, or a plain open/short in the circuit. The repair manual doesn't say any "overspeed" code will be given.

    Because all P0 codes are standardized by SAE, you can see a list of them (including the ones a 2010 Prius doesn't use):

    P0Axx Hybrid Diagnostic Trouble Codes

    You can see there are groups of "drive motor A" resolver codes (P0A3F through P0A44), "drive motor B" resolver codes (P0A45 through P0A4A), and "generator" resolver codes (P0A4B through P0A50). The Prius uses the "drive motor A" codes to talk about MG2, and it uses the "generator" codes to talk about MG1. It doesn't have any other MG, so it would be weird for it to give a P0A4A, which is a "drive motor B" code, ever. Even if it wanted to give an MG1 overspeed code, the one in the "generator" group for that would be P0A50.

    So if it were me I think I'd try to see what codes come up in Techstream, or even just a second opinion from any other decent scan tool.
    Prius-gang07 likes this.