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P0138 Oxygen Sensor High Voltage requires ECM replacement?

Discussion in '1st Gen Tundras (2000-2006)' started by gzip, Jan 23, 2023 at 6:54 PM.

  1. Jan 23, 2023 at 6:54 PM
    #1
    gzip

    gzip [OP] New Member

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    Hi all,

    New Tundra owner and new forum user here. I recently bought a 2006 Tundra Double Cab 4.7L V8 4x4 and ran right into the all too common Oxygen Sensor problem, in particular DTC P0138 (bank 1, sensor 2 High Voltage).

    I installed a new sensor but it didn't resolve the problem. I tried both a Denso 234-4260 and the original Toyota marked part 89465-0C160. The original part that was replaced also passes the ohm meter test found in the Repair Manual.

    The shop ran through the full troubleshooter in the Repair Manual and I've verified most of it as well. The conclusion is to replace the ECM.

    I did notice one strange symptom at the very end of troubleshooting for shorts which is that sensor 2 in _both_ banks runs at around 0.85-0.9V when they are both connected, even tho an error code is only thrown for the one bank.

    Now the strange part. If I disconnect one side or the other then the opposite side falls into range at around 0.4-0.45v. It's almost as if the two banks are being added together when both sensors are connected.

    Given this strange symptom is there anything more I can troubleshoot or is it just another vote for a failed ECM?

    upload_2023-1-23_19-36-38.jpg
     
  2. Jan 23, 2023 at 7:15 PM
    #2
    Jack McCarthy

    Jack McCarthy Navigating the luminiferous ether to see the light

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    Hard to determine what’s happening without seeing the complete circuit. Did you trace it out in the FSM wiring diagrams? Do the 02 sensor outputs each goto their own input on the ECU? Any series resistors present?

    I would examine the ECU and test out the inputs to insure they’re high impedance and not getting pulled to 0.9 volts as it would seem before checking out the wiring harness for anything unusual. But that’s me.
     
  3. Jan 23, 2023 at 7:28 PM
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    shifty`

    shifty` Better to piss in sink than to sink in piss

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    Question: Have you inspected the wiring on all sensors closely to see if it's ever been cut/spliced?

    Have you checked all grounds around the vehicle, tested out connections to the O2?
     
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  4. Jan 23, 2023 at 7:49 PM
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    gzip

    gzip [OP] New Member

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    Haven't traced the entire run for splices but the connectors between the sensor and ecm have been tested for continuity. Didn't note any significant resistance.

    Haven't tested the impedance, what's the best way to do that? Wouldn't the signal lines be consistently pulled up rather than vary when one or the other sensors was disconnected?

    Is it OK to post the relevant section of the Repair Manual to show what's been done? The shop had a wiring diagram that I saw briefly but I haven't come across it in the manual yet.
     
  5. Jan 23, 2023 at 8:02 PM
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    Jack McCarthy

    Jack McCarthy Navigating the luminiferous ether to see the light

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    It’s OK to post the diagram(s) relating to the circuit as it’s been done here several times before. I personally don’t have an 06 FSM manual since I have the 02 Tundra.

    Best to understand it before going much further into checking the ECU which can be done with a multimeter for both an ohm and diode check.

    You can obviously look at it physically for anything wrong as well as the connection from the 02 sensors to it.
     
  6. Jan 23, 2023 at 8:33 PM
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    gzip

    gzip [OP] New Member

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    I pulled the ECU out just enough to see the part number on top. Didn't notice any obvious damage.

    The only thing I see that hasn't been done in the attached document is to test the EFI Relay. It's in there pretty good. Any advice on how to pop that bad boy out without any damage? Not sure what the symptoms of a bad relay would be...
     
  7. Jan 23, 2023 at 8:47 PM
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    Jack McCarthy

    Jack McCarthy Navigating the luminiferous ether to see the light

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    A good relay should have a resistance to it in the 10s to 100s of ohms or so across the coil. A bad one will act as a short (or very low resistance) or an open for a damaged coil. If you had a vendor part number that would be even better because you could look up the coil resistance in the data sheet.

    Best way to check since you don’t have a data sheet is to charge the coil with a voltage to get it to click open or close.

    I’ll have to defer to someone who’s knowledgeable about pulling it.
     
    Last edited: Jan 23, 2023 at 8:54 PM
  8. Jan 24, 2023 at 6:01 AM
    #8
    shifty`

    shifty` Better to piss in sink than to sink in piss

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    EWD collection. That's one of many helpful links in the intro-to-1st-Gen thread.

    I doubt you'd see physical damage, usually people will pull apart the clamshell and see signs of copper oxide on the PCB if water damage (seen a few times, usually in no-start/no fuel conditions), or maybe a burnt trace (never seen this before). I'm doubting it's the case here.

    Main purpose of a relay is to toggle a circuit between two different values: open and closed, or path A and path B. Thus a good indication you have a bad relay is something is always-on/always off, or toggled onto a path/circuit that's unexpected (ex: Fuel pump in always-low-speed or always-hi-speed mode)
     
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  9. Jan 24, 2023 at 6:09 AM
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    BubbaW

    BubbaW Saw it right off

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    From your first post, I was initially going to ask if your reader shows live data and if so, what was your MAF reading. It can affect O2 readings. Also, the 12vdc for the sensors comes from the EFI relay. Our O2 sensors are fed gnd signal from ECM.

    Now that you mention EFI check, I would suggest either checking for 12vdc at the MAF sensor red wire to gnd with IGN ON. Before attempting to pull relay....yes they can be stubborn....I would check the EFI fuses, in particular EFI NO. 2, both of which are in the Eng bay and EFI NO. 2 feeds O2 sensors and MAF.

    EFI NO. 2.jpg


    On a side note....there is no Z in DC !
     
    Last edited: Jan 24, 2023 at 6:17 AM
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  10. Jan 24, 2023 at 11:06 AM
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    gzip

    gzip [OP] New Member

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    The EFI relay and both fuses are good. The relay came out relatively easy with a gloved hand a continued wiggle. Tested open then applied a 9V battery across the leads and heard an audible click and the relay closed.

    I do have live data, attached is a screenshot.

    Screenshot_20230124-113348.jpg
     
  11. Jan 24, 2023 at 11:37 AM
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    BubbaW

    BubbaW Saw it right off

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    MAF reading looks decent according to FSM tolerances(2.0 to 3.9 g/s: Idling) or somewhat close to Eng size of 4.7 which is what some folks use as a rule of thumb

    O2 readings are best read after Eng is normal operating Temp and at idle. From those high readings and 152 temp, my first thought is Eng is still trying to warm up, RPM is high, with the O2 readings showing rich condition.

    Would like to see those readings again, along with both bank sensor 1 after normal temp at idle

    Edit to add....
    Just saw that and have to say, "Do what". Definitely a head scratcher or if it's coming from gauges presentation, makes me wonder if you accidently ask for S1 and S2 but actually chose S1 and S1, yep sounds crazy even typing it !
     
    Last edited: Jan 24, 2023 at 12:05 PM
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  12. Jan 24, 2023 at 4:46 PM
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    gzip

    gzip [OP] New Member

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    Here it is warm at idle (note that B2 was fluctuating between ~0.2 and 0.7):

    upload_2023-1-24_16-35-25.jpg

    (For some reason O2S1 has no bank associated with it and that's the only one.)

    And here it is while driving after releasing the gas and coasting:

    upload_2023-1-24_16-39-7.jpg

    I'm using a dirt cheap elm327 bluetooth adapter and a free app so errors and bugs are a possibility.

    In the meantime I've ordered this ECU, hopefully these guys are legit:

    89661-0C731 for 2006 TOYOTA TUNDRA 4.7L ECM ECU PROGRAMMED PLUG&PLAY
     
  13. Jan 24, 2023 at 5:25 PM
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    shifty`

    shifty` Better to piss in sink than to sink in piss

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  14. Jan 24, 2023 at 5:36 PM
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    BubbaW

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    Yeah, hard for me to interpret those readings.
    Might be misunderstanding you but we have 4 sensors, 2 in front of TWC and 2 behind.
    Front sensors should read from approx .8vdc(rich) to .2vdc(lean) in a sine wave pattern.
    Rear Sensors should not oscillate like the front sensors, rich to lean but some what of a straight line reading.
     
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  15. Jan 24, 2023 at 8:21 PM
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    assassin10000

    assassin10000 New Member

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    Download torque (torque lite is free) and it has an option for graphs. It's what I use.
     
  16. Jan 26, 2023 at 8:57 AM
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    gzip

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    Right, it's just an issue with my app which only has one display option for S1. Maybe it assumes they will always be the same value, not sure. I've installed Torque Lite as well and will have to give it a whirl.

    3 questions...

    The manual says over 0.6V is high. So both downstream/front sensors continue to run rich altho bank 1 is even moreso. Why would one side run richer? I'm not sure why the code only fires for bank 1. Does the system check continue after the first fault or does it just stop there? The other option is that the fault only triggers above 0.8V, which the following freeze frame shows, but the manual says nothing about. Anything else stand out in the freeze frame?

    P0138-Freeze-Frame.jpg
    P0138-Freeze-Frame2.jpg
     
  17. Jan 26, 2023 at 9:13 AM
    #17
    shifty`

    shifty` Better to piss in sink than to sink in piss

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    Why would one side run richer? A few reasons. Fuel is metered based on what the MAF sees incoming for air, and what the pre-cat O2 on that bank sees for fuel/ox ratio after combustion, in some cars it'll factor in throttle position/butterfly position/other sensors to the equation, I'm not sure about this specific engine.

    It could suggest the pre-cat O2 on that side is reading 'off', or you have a pre-combustion/post-combustion leak, or the ECU isn't getting an accurate depiction of how much air is actually coming into the intake. I mean, I suppose a vacuum leak could potentially cause wonky stuff like this, but ...

    Given it's not doing this on both banks, I doubt it's anything between the throttle body assembly and the filter box.
     
  18. Jan 26, 2023 at 10:01 AM
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    BubbaW

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    A few things do indeed stand out, but as mentioned before, it's best for some/most of these checks to be at idle, full warmed up eng with proper temp(you are @ECT of 187deg) and Cat's good and hot,(you are @1900deg).

    Setting aside you are moving 37MPH at 1900RPM, the LTFT +17 stands out(positive reading can indicate an air leak)....anything over 20> you're gonna throw a code. The MAF reading, even @ 37MPH/1900RPM, is bonkers at 41 g/s....2 to 7 g/s at idle and maybe 15 to 25 g/s at 2500 rpm are considered somewhat normal.

    Have you cleaned your MAF, checked your air filter box for oil(possible bad PCV), is air filter good and what kind.

    There could more I'm not mentioning but I would check for air leaks, check MAF below instructions, air filter condition and recheck again BUT at IDLE fully warmed up with CATS hot like before.
     
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  19. Jan 26, 2023 at 10:11 AM
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    gzip

    gzip [OP] New Member

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    Fwiw, we were climbing a hill for a while when the code triggered. I was trying to stay under 40 during the trip since that's the minimum that the drive cycle specifies. I'll check everything you suggested.
     
  20. Jan 26, 2023 at 11:33 AM
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    gzip

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    MAF sensor is super clean.

    20230126_120133.jpg 20230126_120140.jpg

    Air filter is pretty clean, based on the part # it looks like it's brand Premium Guard. There's no oil in the filter box.

    20230126_113345.jpg
    20230126_113336.jpg

    Waiting for temps to even out before attempting an evap ready cycle, then I'll get you those numbers on idle.
     
  21. Jan 26, 2023 at 11:48 AM
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    BubbaW

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    I have never had a need to check the # 1 step in the below MAF Inspection but I have for chits and grins did the # 2 check.
    While I agree your MAF looks good and don't wish to run you down a rabbit hole but if time permits, do those checks if you wish just to see what it shows ?

    MAF.jpg
     
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  22. Jan 26, 2023 at 12:40 PM
    #22
    shifty`

    shifty` Better to piss in sink than to sink in piss

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    Just a point to make: Coatings on your MAF aren't necessarily visible, dust is enough to make weird things happen. My MAF looked cleaner than yours, actually. I cleaned mine a couple tanks ago, probably for the 1st time in its life, and saw improvements. 1.5mpg+ and more noticeable throttle response. Just make sure you use an apropos cleaner designed for MAFs, and let the part come to ambient temperature before reinstall, the cleaner product will make it icy cold.
     
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  23. Jan 26, 2023 at 1:22 PM
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    gzip

    gzip [OP] New Member

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    Down the rabbit hole we go. I'm getting some strange readings here. At 20k it shows 1/open. At some of the higher settings it only flashes a value then goes to 1. I only got a steady reading of 1733 at the 200k setting. (It's about 50 deg F out.) Looks way off the chart right, is there no DTC for this type of condition?

    Is it even worth doing the #1 check now? I was thinking about trying a 9V battery as source.

    BTW, does the MAF provide IAT as well or is that a different sensor?
     
  24. Jan 26, 2023 at 1:28 PM
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    BubbaW

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    Gonna answer this and then attempt to decipher those readings :eek2:

    The MAF does indeed have the IAT inside it also. Those 2 resistors you're showing in your picture....one for MAF reading and one for IAT.
    BTW, where did you get that PBT-GF40 and what is MFG name ?

    Never done or needed to do # 1. We like others being Guinea pigs. Knock your self out and yes on 9v. I use a 9 vdc transistor radio battery(what we called in the 70's) for a number of tests as long as it's not large current draw which a MAF won't be.
     
    Last edited: Jan 26, 2023 at 1:35 PM
  25. Jan 26, 2023 at 1:41 PM
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    gzip

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    20230126_143420.jpg

    I've had the truck a little over a week. The MAF is likely from the dealership or an original.

    Interestingly enough I've been waiting for my IAT to fall into range for hours but it remains higher than ECT.
     
  26. Jan 26, 2023 at 2:04 PM
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    BubbaW

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    Blow in it....TWSS !
    Possibly help with equilibrium between the 2 :confused:

    Not necessarily a caution but just so you know, if you unplug MAF with key in IGN ON position, you will set an immediate code, possibly P0102 will strike first detecting low input to MAF.
     

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