DTC P0138 at highway speeds

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Prius Pete, Feb 29, 2008.

  1. Prius Pete

    Prius Pete Active Member

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    My 2004 got a check engine light. Code P0138 means high voltage from the post catalytic converter oxygen sensor. The dealer replaced the sensor (cost me $400) and cleared the code but it still comes on at highway speeds. I bought a Scangauge so I could try to understand what is happening. I can drive all week in the city with no error. As soon as I go on the highway, the light comes on within a minute or two. If I clear the code while driving on the highway, it comes back on in a couple of minutes.

    Gas mileage seems normal and the car behaves fine. I'm reluctant to let the dealer do more trial-and-error parts replacements at my expense. Anyone have any ideas?
     
  2. lumpy95

    lumpy95 Member

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    My first suspect would be whoever replaced it.
    In the Haynes manual instructions for replacing it there are some major warnings about special handling and replacement instructions. Evidently the sensor is very fragile and won't tolerate a number of things, especially involving the electrical connections.
     
  3. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    Shouldn't this replacement have been covered by the federally mandated emissions control system warranty?
     
  4. jayman

    jayman Senior Member

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    Canadian gasoline contains MMT (Methylcyclopentadienyl manganese tricarbonyl) which can adversely affect O2 sensors and catalytic converters. The emissions warranty on Canadian model vehicles is generally shorter than US Federal emissions warranties

    The ACEA (Association des Constructeurs Européens d'Automobiles)conducted tests and determined that there were apparent increases in emissions - and fuel consumption - by 50,000 miles using MMT gasoline. By 100,000 miles, the difference was significant, especially for emissions

    Ethyl Corp - the same nice folks who put lead in gasoline - have an army of lawyers and are always fighting the removal of their cash cow from gasoline.
     
  5. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    My bad. I did not notice that the OP is from Canada.:doh:

    I do know that US laws do not apply north of the border.
     
  6. jayman

    jayman Senior Member

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    No worries. Here, have a drink on me

    Gluk-gluk-gluk-gluk-gluk-gluk-gluk <clink>
     
  7. Bob64

    Bob64 Sapphire of the Blue Sky

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    Perhaps that gas damaged the catalytic converter?

    If the problem is not the sensor, then its likely that the Catalytic Converter might be faulty...
     
  8. jayman

    jayman Senior Member

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    There should be two O2 sensors, one before the catalytic, one after. The one after is responsible for performance measurements of the catalytic. This could turn out to be a pricey repair

    In Canada, Toyota only provides emissions coverage for 36 months or 60,000 km, with some parts only covered for 24 months or 40,000 km. The 96 month or 130,000 km emissions coverage in Canada has many exclusions

    If you're interested, the ACEA has very specific evidence of emissions control equipment damage running MMT gasolines. This is in their WWFC report

    http://www.acea.be/images/uploads/pub/Final WWFC 4 Sep 2006.pdf

    The discussion of MMT starts on pdf page 26, near the bottom of the page. Many photos are included
     
  9. Bear68

    Bear68 Member

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    Just to get technical here... There is only one O2 sensor.... The front sensor is an air/fuel ratio sensor. Much more reactive and sensitive and also much more expensive.....


    BTW A/F sensors and O2 sensors are only covered 3 year 36000 miles in the USA. The catalytic convertor is 8/80.
     
  10. Prius Pete

    Prius Pete Active Member

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    That explains why my Scangauge only gets a reading from O12! The O12 oxygen sensor reading rises from 0 to 84-93 when warmed up. I can drive all week with no CEL, but as soon as I get up to 60 mph or so, the light comes on in a minute. If the trip has set the light, then I slow down and clear it, I'll get another P0138 even if I stay at a low speed (same trip without shutting down). The gauge shows "closed loop" continually once warmed up but the freeze parameters captured with the P0138 always shows "open loop".

    It seems to me like the oxygen sensor is working. Since I can drive a lot with no code, I think the catalytic converter is working -- at least most of the time. I'm wondering if it could be related to fuel trim. I think the car learns the fuel trim and stores it in memory somehow. Maybe this needs to be reset.

    Thanks everyone for your comments.
     
  11. kocho

    kocho Member

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    Did you provide this TSB information to them?

    http://www.vfaq.net/docs/TSBs/EG018-03.pdf

    Not sure if you are still in warranty though...

    Anyway, having similarly high-way only DTC code (P0420), I can tell you my guess why you are getting your DTC at high-way only. It is that the car computer would not even attempt to perform certain diagnostic tests unless you are driving on the highway after the car has reached certain state. Look at the TSB above for conditions for this code. Basically, your "readiness" status would never be "ready" if you never go thru the compete set of diagnostics the computer does. And that would never happen if you do not drive on the highway. In my case, I could drive for weeks and not get the code but my emissions system check readiness was "not ready". Once I got on the highway, the car went thru the diagnostic cycle and sure enough the DTC would come-up.

    Not sure however how to diagnose/repair your problem. Mine was a clear-cut Cat Converter failure so I had to replace the cat converter, reusing the old O2 sensor and it worked great. Btw, the sensor part can be had from Toyota for about $100. Charging you additional $300 labor is a little excessive IMO to replace it...
     
  12. Prius Pete

    Prius Pete Active Member

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    Thanks kocho for the TSB. My 2004 is after this -- so it does not apply to me. My understanding of this TSB is that the codes happened due to burning off some "new car" deposits somewhere. My car has 95000 km, so it is definitely broken in. My full-vehicle warranty is gone but I have a bit left on my drivetrain warranty. This only covers certain specific items, apparently not related to the exhaust system.

    You might be right that there is a diagnostic that runs and fails at highway speed. My scangauge says "Ready", once I clear the code. I thought that meant ready for emissions testing.

    The dealer price for the O2 sensor was $267. With labor and tax it came to $400.

    Maybe it's my catalytic converter. Maybe I damaged it driving over a snowbank or something. I don't plan to replace it "just in case" unless I really have to.
     
  13. patsparks

    patsparks An Aussie perspective

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    An out of range oxygen sensor would most likely be caused by an exhaust leak. Air (oxygen) getting into the system or the engine is misfiring.
     
  14. kocho

    kocho Member

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    This is certainly true for emission systems. If you clear codes, unless the ScanGauge does it somehow differently, the I/M status should *not* be ready immediately. I think ;). In my '02, after I clear a code my scanner says "I/M status not ready". It is not a scanGauge but a generic OBD-II scanner with "Live View", so similar to ScanGuage I suppose. It takes me several days and highway cycles of 5 minutes over 55 mph to clear all the emission system checks and then the status becomes ready.

    Dealer prices I find often are inflated. I have checked the price from ToyotaParts4u.com and I've seen a quote on these forums for another online/phone Toyota dealer at around $109. But this is for the rear O2 on a '01-03 model. Not sure if the rear O2 sensor on the '04+ is different/more expensive though (I think only the front is different on the newer Prii but I might be wrong here).
     
  15. jayman

    jayman Senior Member

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    Not in the mood to jack up my Prius, so I will take your word for it. Didn't pay much attention to the catalytics on my FJ, but I thought a month ago when I greased it I noticed O2 after the cats. Perhaps just a truck thing
     
  16. jayman

    jayman Senior Member

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    It wouldn't hurt to inspect the plugs, though a misfire should also set a CEL. An exhaust leak, well I wonder just how much effort that Toyota dealer put into fixing the problem.

    Using the genuine Toyota scantool, it would have been easy to look at live data and confirm the performance of the O2 sensor.

    Additionally, they should have done the drive cycle as suggested by the TSB. If they are only willing to replace parts until the problem is "fixed" it's time for him to find a different dealer
     
  17. lumpy95

    lumpy95 Member

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    True, according to the Haynes manual.
     
  18. jayman

    jayman Senior Member

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    Ok checked the TIS manual. Yep, one O2
     
  19. Bear68

    Bear68 Member

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    A/F sensor before the cat tells the ECU how to adjust fuel trim. O2 sensor after the cats tells the ECU how well the cats are functioning.:attention:
     
  20. rick57

    rick57 Member

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    Sorry kocho, but I just checked and that TSB is listed as Obsolete by Toyota. The revised one is EG038-04 and involves reflashing the ECU. Not sure about the dealers north of the border, but here in the states,we are now using a new diagnostic tester, Techstream. It is a notebook that took the place of the previous tester. By going into the Health Check section, any updates for any calibrations will be highlighted here. It is a lot faster and does more then the older tester. According to TSB, the warranty is for 96 months or 80000 miles,whichever comes first. Have the dealer recheck for any updated calibrations, Prius Pete, which may take care of your condition. Not sure if Canada is different in calibrations, but it might be worth a try.
     
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