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Discussion Starter · #1 ·
Hello there,

Questions:

  1. What (if any) do I need to disconnect? for e.g. AUX 12 v battery before replacing O2 Sensor or Spark Plugs?
    • Typically when should I disconnect the battery, on what kind of DIY
  2. How to troubleshoot p0171 (NO check engine light, only Maintenance Light)
  3. How to replace the Air ratio fuel sensor: where is the harness connected - HiHL seems different from the gas version

HiHL: 3mzFE 170K: 07 V6 Hybrid engine AWD

Guidance please: I am trying to trouble shoot p0171 (the only code)

  • NO: check engine light (has not come on)
  • YES: needs maintenance light??
  • Scanning OBDii, shows p0171 B1S1 with short fuel trim at 25 (warning, the codes were reset 50 miles ago, this data is from the freeze frame)
  • 2500 miles since last oil change
  • Yes: mild oil pan gasket leak, but levels seem fine
  • Car does not hesitate, runs smooth


Steps I have done so far:

  1. The MAF was dirty, I cleaned it out with CRC.
  2. B1S1 only, so its not the MAF right?
  3. B1S1 only, so not a vacuum leak right, else the MAF would go off?
  4. Fuel injector check/clean: sticky/ fuel filter issues, poured 12 oz Chevron Techron
  5. Does not hesitate, so its not the coil packs or spark plugs correct? Or is it because the electric engine is keeping it smooth?

  • Do I need to take off the plenum to get to the Air Fuel Ratio Harness for Bank 1 Sensor 1?
  • Do I need to take off the undercar/ underbody shield?
  • Do I need to disconnect the battery
  • Do I need to reset anything after change, like the check maintenance light?
Pictures of the OBD scan codes

http://imgur.com/a/HecCz :help:

thanks
 

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This is followed by about ten pages of diagnostics. I'd recommend starting Alldata DIY account, it's $40 for 5 years, then you can see all the goodness. Too much for me to post here for you.
You may also look into obtaining a Toyota specific USB to OBD2 port cable, downloading Techstream s/w - it's free - and connecting laptop to your system, All diagnostics are Techstream or equivalent scanner done.
 

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Btw, how is air filter? You may have as simple as air leak somewhere in air ducts, causing lean condition.
 

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Discussion Starter · #4 · (Edited)
@ukrkoz you rock :chug:, this gives me a check list to start with,hunt down. While following the list, I discovered the radiator fluid was low (thanks for that, still checking) - not sure what that has to do with Bank 1 Sensor 1 lean.

Air filter: I had it replaced, you know I was wondering why the fit did not seem very snug... actually it looks fairly clean... so I was wondering the same thing, how would I check if it has a leak, no holes; but MAF was dirty (and I cleaned it), so it could be air getting through. But MAF would catch the lean and compensate right>

  • Can I use any pink/red radiator fluid or should I use only toyota? I have been using all OEM stuff, and been getting fairly expensive!
  • Can you please tell me if I need to disconnect the 12v battery, to test/replace the O2 Sensor (open/short circuit)/or the spark plugs.
  • Is the AirRatio-O2 Harness in the same place as the Gas version? (I ask because the Air Intake seems to be relocated (from comparing with the Gas highlander) to make room for the power-inverter.), can I reach the harness easier in this than the Gas version
  • Where is the EGR valve please, easy to reach?

BTW - what is the humming noise, everyonce in a while, even after stopping the car, I hear some noises/electrical ? wondering if its high voltage or just some pump.
 

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@ukrkoz you rock :chug:,
I don't drink, thank you.>:D

this gives me a check list to start with,hunt down.
No. You should see entire diagnostic procedure just for those 2 codes on Alldata!!

While following the list, I discovered the radiator fluid was low (thanks for that, still checking) - not sure what that has to do with Bank 1 Sensor 1 lean.

You need to really look into this. Use dye or whatever else possible, to determine if your water pump is not leaking. On TCH-s for those years, unti 2010 models, we were plagued with leaking pumps.

Air filter: I had it replaced, you know I was wondering why the fit did not seem very snug...
No doubt it's clea, but if you do not have sealed fitment anywhere past it, too much air is going into the system and then O2 catches on this and tells ECM.

actually it looks fairly clean... so I was wondering the same thing, how would I check if it has a leak, no holes; but MAF was dirty (and I cleaned it), so it could be air getting through. But MAF would catch the lean and compensate right>

  • Can I use any pink/red radiator fluid or should I use only toyota? I have been using all OEM stuff, and been getting fairly expensive!
I use Prestone that says "compatible with any color any make antifreeze".


  • Can you please tell me if I need to disconnect the 12v battery, to test/replace the O2 Sensor (open/short circuit)/or the spark plugs.
Once again, you need quality scanner to check on the system - or, laptop with Techstream connected and running diagnostics. 12V is not quite doing same thing it does in conventional cars, it's simple backup power source for ECM, security, clock. I honestly never had 12V disconnected on conventional cars and had no issues. But I know that you taking quite a chance for your system to go nuts if you DO disconnect 12V. Your call.


  • Is the AirRatio-O2 Harness in the same place as the Gas version? (I ask because the Air Intake seems to be relocated (from comparing with the Gas highlander) to make room for the power-inverter.), can I reach the harness easier in this than the Gas version






Do not forget, this is 2012 Alldata vehicle account.


  • Where is the EGR valve please, easy to reach?
BTW - what is the humming noise, everyonce in a while, even after stopping the car, I hear some noises/electrical ? wondering if its high voltage or just some pump.

Noise is very normal. It's brakes accumulator. Get used to it. Those cars "talk" all the time.
 
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