P0138 code problems - Page 2 - Toyota RAV4 Forums
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#11 (permalink) Old 01-26-2011, 02:14 PM
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looking at the diagram its not saying that the voltage for the heater is high, its saying the sensor is reading higher than it should right?
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#12 (permalink) Old 01-26-2011, 03:18 PM
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Quote:
Originally Posted by wake_100
looking at the diagram its not saying that the voltage for the heater is high, its saying the sensor is reading higher than it should right?
If the ECM had detected a problem with the heater circuit, you would have obtained a P0037, P0038 or a P0141 code. You can look at the following PDF file for information on troubleshooting one of these codes. Link

Your code, P0038, indicates that the voltage seen between pins 64 & 87, on the B30 connector of the ECM, is higher than it should be. Pins 64 & 87 at the ECM are connected to Pins 3 & 4 (respectively) on the O2 sensor.

I don't know if you have a Scangauge, or if you were just asking out of curiousity, but if you do, use it to see if the O2 readings are changing, or if they are locked at a fixed value.

If you see the voltages are fixed, then unplug the O2 sensor and see if they drop to zero. If they drop to zero, then the high voltage is coming from the sensor. If the voltage doesn't drop, then it is coming from a short circuit within the harness, or it is a defective ECM.

If you don't have a Scanguage, then unplug the sensor and you should get a P0137 code ( a low voltage error). If you don't get the P0137 then you still have wiring problems.

Be aware that when you unplug the O2 sensor you will also get a P0037 ( and possibly a P01410) because the heater circuit will also look failed.
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#13 (permalink) Old 01-26-2011, 03:24 PM
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I dont have a scanguage, really thinking about getting one now... Thanks for your help so far. I have an appointment tomorrow to take it to the dealership and see how badly they try to rip me off... :/

and why does it take 20 minutes to almost an hour for the light to come back on? i would think there would be a faster response from the ECU
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#14 (permalink) Old 01-26-2011, 03:47 PM
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Did you ever say which sensor you changed? Hope it was the downstream sensor: http://www.obd-codes.com/p0138
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#15 (permalink) Old 01-26-2011, 03:54 PM
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kinda, maybe I wasnt clear but yes it was sensor 2 also known as the downstream sensor. the one after the cat. im wondering because it was a bosch sensor i replaced it with also :/ I ohmed out the original sensor according to the service manual and it checked good
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#16 (permalink) Old 01-27-2011, 12:53 AM
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#17 (permalink) Old 01-27-2011, 08:12 AM
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Okay. I only got P0138 and the O2 sensor didn't fix it. I see a lot of talk that the sensor life span is 100K miles. I am at 88K... Just out of the emission warranty also :/
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#18 (permalink) Old 01-29-2011, 08:40 AM
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Took it to the dealer and it turned out that sensor 1 was the one that was bad.
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#19 (permalink) Old 01-29-2011, 10:04 AM
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It may not be the sensor. The system uses two O2 sensors, a narrowband one in the exhaust manifold to set the air/fuel ratio to 14.7:1. The downstream one is a wideband which checks if the AFR is set right AND the catalytic converter is doing its job.

My RAV4 replaced a Subaru Forester which kept giving a downstream code which I didn't believe was the sensor itself partly because as you mentioned it doesn't come on instantly. On eBay I found a listing for a catalytic converter that said "keeps the code (they gave the specific one) from repeatedly coming on." Bought and installed their converter - end of problem.

Quote:
Originally Posted by wake_100
Took it to the dealer and it turned out that sensor 1 was the one that was bad.
Okay, my post overlapped your latest. Replacing the narrowband sensor is a lot easier than the cat!

Fred
2006 RAV4 V6 4WD Red Limited - wife's
2006 Accord V6 Hybrid - Dr. Dyno's - quick as the RAV but +8 mpg
2003 Odyssey V6 - handy people & cargo mover
1999 F-250 4X4 Diesel - snow plow, Bully Dog chip
2001 F-250 4X4 Diesel - truck camper, TS chip, 20' bike/trike dyno trailer
2004 Suzuki DRZ-400S Dual Sport

It's the pedal (or the handgrip) on the right!!
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#20 (permalink) Old 02-26-2014, 12:36 PM
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Angry

Have a P0138 code on 2006 Rav4 (secondary O2 sensor). Installed a new Bosch O2 sensor and cleared the code. Check engine back on in a few trips, same code.
Brought my scan tool over to view live data. The rear O2 showing zero voltage.
At the 4 wire connector FROM the vehicle, one wire has 12v for the heater, guessing 2 other wires are eventual grounds, but isn't the 4th wire suppose to have a reference voltage for the O2 sensor? Something like .3 to .5 volts?

Trying to determine if it's related, but just prior to the check engine light illuminating (a few startups ago) the Rav4 was at the Toyota dealer for a recall regarding the sticking throttle situation, involving a software upgrade and some cable replaced. Unsure if they touched or replaced the ECM.
Vehicle starts and runs fine, no drivability issues.
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