Intermittent C1239, C1241 C1467

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Nick Seifert, Apr 21, 2024.

  1. Nick Seifert

    Nick Seifert Junior Member

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    Prius Chat brain trust:
    I've browsed and searched the Gen3 forum, finding similar but not identical threads on this topic.

    C1239 and C1467 Left Rear | PriusChat
    ABS C1467 Faulty Rear Speed Sensor Left | PriusChat
    Xmas Lights situation: Slip+ Brake Trouble + yellow Electric Park + ABS with BLINKING Cruise Control | PriusChat

    rather than re-start / hijack one of those, a new thread...

    My symptoms are:
    • when driving, intermittently the traction control will light up, seemingly for little to no reason.
    • After a few of these TC turn on events, the expected ABS fault light combination comes up.
    • The ABS fault lights seem to come on when cruise control is turned on as well.
    • The lights usually clear after a vehicle restart, and/or a bit of driving.
    • While the ABS lights are active, regen braking is effected / non-functional.
    • When scanned i'm seeing C1239, C1241, and C1467.
    The main difference i have from the threads above:
    • The C1241 code is not mentioned by other threads. It is a relatively new 12V AGM battery. no other known issues.
    • Maybe worth mentioning this is the Plug in Prius model. IDK.
    • I recently (approximately 6 months ago) replaced the rear wheel bearing assembly with a Timken, purchased from RockAuto, so i assume not a counterfeit part...

    As for diagnostic work, so far:
    • I removed the both rear wheels, and measured resistance of the speed sensors:
      • Left sensor reads 200kOhm with leads in one orientation, approximately 2Mohm with meter leads swapped. This is the sensor reported bad.
      • Right sensor reads 4MOhm with leads one way, ~40MOhm with meter leads swapped.
      • Left and right harness resistance readings were similar, very high MOhm, both meter lead positions.

    All signs here are pointing to a bad wheel sensor... i'm just surprised given it's new.

    Any other thoughts or ideas for how to further diagnose this?
     
    #1 Nick Seifert, Apr 21, 2024
  2. ChapmanF

    ChapmanF Senior Member

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    Well, the code isn't about the voltage at the 12V battery, but the voltage arriving at the brake system. What voltage readings there are shown in your freeze frame for the C1241?

    It might be tricky to interpret that; these sensors are not simple coils with a resistance to measure. They are active electronics producing digital signals, and what 'resistance' they appear to have to an ohmmeter might not indicate much. (I'm also not sure whether they like being probed with reversed voltage.) The troubleshooting instructions in the manual never mention using an ohmmeter on the sensor, only on the wiring. It concludes the sensor is probably at fault if the wiring isn't.

    You could give some more details here. The troubleshooting instructions give multiple readings to take, of the little extension harness at the back and also of the main harness from there up to the ECU. Naturally, they want low (< 1 Ω) readings between pins that are supposed to be connected, and high (> 10kΩ) readings between the ones that aren't, or to body ground.

    The voltage supplied by the ECU to the sensor is also checked in one step. As the ECU has given a code about the supply voltage it is getting, I suppose there's a chance it's also struggling to supply the sensor with the spec'd voltage.
     
    #2 ChapmanF, Apr 21, 2024
    Nick Seifert likes this.
  3. Nick Seifert

    Nick Seifert Junior Member

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    Thanks for the suggestions and feedback, ChapmanF.

    Unfortunately i do not see any freeze frame information for C1241. The faults are not always present and don't always stay latched after a vehicle restart. I tried to reproduce the issue today, but no luck. Possibly this is an OBD2 scanner issue? or maybe just no freeze frame data? Any suggestions would be appreciated about how or when to get freeze frame data.

    I have an older OBD2 scanner i purchased its "enhanced diagnostics" and I'm now also seeing a P1578 code. Based on this post it looks like that might have come through when the cruise control was on and this ABS fault happened. Seems related but like a symptom not the cause.

    I have not used TIS before, but digging into diagnostics may be my weekend project.

    When this happened while driving it felt like the disc brakes were working just fine. No changes in brake fluid level. Any concerns about driving the vehicle? I'm comfortable with no ABS/TC for short periods, i'm in rural driving with little traffic.
     
    #3 Nick Seifert, Apr 22, 2024
  4. Nick Seifert

    Nick Seifert Junior Member

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    No recurrence of this issue still. I'll update if this changes.
     
    #4 Nick Seifert, Apr 28, 2024
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