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O2 Sensor Troubles

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by voltech444, Apr 14, 2018.

  1. voltech444

    voltech444 Junior Member

    Joined:
    Oct 2, 2016
    25
    36
    3
    Location:
    Pontiac, MI
    Vehicle:
    2006 Prius
    Model:
    Two
    So got a 2005 Prius with 244k, had a MIL come on, scanned car, got a P0037, upstream A/F B1S1 (wideband O2) sensor. Since the mileage is pretty high, I did a complete fuel system cleaning with a pressurized cleaning machine I bought, first I clean throttle plate and body, then use spray wand (with MAF disconnected and moved out of the way) and spray 100% seafoam fine mist into intake while engine is running. Then I disconnect the fuel pump, plug fuel line, and hook up the cleaner to the fuel rail, run 50% seafoam 50% ethanol free 90 octane gas (17oz total). I've done this on 5 prii including my own and got the process down pretty good. So I did the cleaning, and changed the plugs, then I replaced the upstream O2 sensor. Car ran good for first two miles before MIL came back on, this time it showed P0137 downstream O2 (B1S2) circuit low voltage. The downstream is real easy to change and I had one I ordered off Ebay, direct fit no splicing required. Put it in, drives great but guess what, MIL back on with same code P0137. I've gone over all the common stuff, 12v, maf (cleaned it with maf spray), oil level, checked for any intake or exhaust leaks, I have to search more for a vacuum leak but couldn't find anything so far. I saw one other thread on here where somebody had the same issue but nobody ever responded after their post. I'm wondering if theres a problem with the cat but theres codes that are specifically for that but I don't have any, just the P0137. When I get the car back again i'll have to test the circuit, its possible its not getting adequate voltage or theres a problem with the ECM, but 9/10 its something stupidly simple, probably a bad connection somewhere in the circuit. Any thoughts or help is greatly appreciated!
     
  2. voltech444

    voltech444 Junior Member

    Joined:
    Oct 2, 2016
    25
    36
    3
    Location:
    Pontiac, MI
    Vehicle:
    2006 Prius
    Model:
    Two
    Just wanted to give an update on this problem child. When I increase fuel injection by 12.5% on TS, the rear O2 starts reading 0.8v, when I return it to 0% the sensor voltage drops back to 0.05v. I've back probed the connector on the sensor with the car running and I get the same reading as what I see on TS. This means the circuit is working, and the ECM can read it accurately. Basically this car is running lean. I have a couple Prii around so i've been able to swap parts from a known working vehicle to see if I can get the sensor to read correctly. I swapped the MAF, the rear O2, I cleaned the throttle body, removed the fuel injectors (bench tested and cleaned them), cleaned the fuel rail, double checked the timing (its good), removed and cleaned and bench tested the cam phaser solenoid (and the filter screen for it). When I took off the fuel rail, the electrical connectors on the fuel injectors were filled with engine oil (I can't find how they got filled with oil, no obvious leaks from valve cover) I cleaned them real good, still no dice. I found a ground wire that looked like it was connected, but it wasn't (the ground that goes from front hood area to engine block near the cam phaser solenoid) still didn't make any difference. Can't find any intake or exhaust leaks. Going to try adding another ground to the ECM. When started in maintenance mode, the engine idles kind of rough. It stalled on the customer before (with the only code being the P0137) which doesn't make sense, most vehicles only use the rear O2 to measure OSC of the cat, from what i've read about Prius it looks like it does use data from rear O2 to adjust fuel trim, but it shouldn't make the engine stall, that to me proves there's something else thats causing this. Heater circuit for both O2 sensors are working. The cam phaser works when commanded by TS. I'm almost at the end of my rope here, could this really be a bad ECM? I can't find very many cases of this happening in Prii but at 245k I guess its possible.
     
  3. voltech444

    voltech444 Junior Member

    Joined:
    Oct 2, 2016
    25
    36
    3
    Location:
    Pontiac, MI
    Vehicle:
    2006 Prius
    Model:
    Two
    Here's a video i made:
     
  4. audiodave

    audiodave Active Member

    Joined:
    Feb 3, 2017
    783
    268
    0
    Location:
    US
    Vehicle:
    2004 Prius
    Model:
    Five