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sprinkles08
sprinkles08, ASE Certified Technician
Category: Toyota
Satisfied Customers: 21583
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I received a p0161 code for my 2002 Tundra. Replaced Bank 2

Customer Question

I received a p0161 code for my 2002 Tundra. Replaced Bank 2 sensor 2 O2 sensor and check engine light still reads same error. It keeps coming back on. Replaced it again. Same problem.
JA: Does the light stay on, or does it blink?
Customer: Stay on
JA: Are you fixing your Tundra yourself? What have you tried so far?
Customer: Yes. Replaced sensor
JA: Anything else you want the mechanic to know before I connect you?
Customer: I wouldn't know what else to do
Submitted: 1 month ago.
Category: Toyota
Expert:  Genchi Genbutsu replied 1 month ago.

Thank you for allowing me to help you with this concern today and am sorry to hear that this is happening. I will have to ask you a few questions so that I can get a better understanding as to what may be going on with your Tundra.

This is a rare code that we dont see too often and the fix is usually not the sensor itself. Just to ask, what brand sensor are you installing? Denso brand?

.

Customer: replied 1 month ago.
I specifically purchased Denso because I know the OEM part is Denso. I purchased 2 of them. In researching the code on the forums, it appeared that it is a common problem from what I read. Since it's very easy to access and replace, I replaced BOTH bank 1 and 2 downstream sensors. Upon replacing the downstream sensor from bank 2 sensor 2, I started the car, drove it and the light came back on. I thought it highly unlikely but I read that a couple people purchased new sensors that were bad so I swapped the 2 new rear sensors thinking if the sensor was bad, then I would get a new code from the Bank 1 sensor 2. That did not happen. It was the same code, p0161. Not sure what else it could be.
Expert:  Genchi Genbutsu replied 1 month ago.

It sounds like you have some knowledge in this. So the P0161 is a low voltage circuit code on B2S2 which is located on the passenger side, rear O2. The problem we see with this is usually a bad ecu or connector/wiring issue. The first thing we do is check for voltage at the ECU and depending on what we find will then check the continuity of the wiring. Is something you are capable of doing?

Customer: replied 1 month ago.
With a couple pictures of locations and location of the leads to test, I would be able to.
Expert:  sprinkles08 replied 1 month ago.

Hello and welcome to JustAnswer!

This code is for a heater circuit issue for the right downstream sensor. The heater circuits are powered constantly and ground is duty cycled by the engine controller to control the heater. The problem may be wiring but could still be the sensor. Even though it's the same vendor that supplies the factory sensor if you buy one from a parts store it's substantially cheaper for a reason, it isn't the same sensor. I've seen many cases of aftermarket sensors from the same vendor as factory, Nippondenso included, still set codes. The heater circuit resistance characteristics of aftermarket sensors are often incorrect.

What you need to do is test for power on the red wire at the sensor connector when running. If ok then the yellow heater driver wire needs to be tested between the ECM and sensor for an open or short.

Customer: replied 1 month ago.
Why then when I swapped the 2 newly installed downstream sensors, then swapped them, didn't it trigger the Bank 1 sensor 2 to show a code? Could you tell me the location of the wires to test?
Expert:  sprinkles08 replied 1 month ago.

If you moved a known good sensor to that location, cleared the codes and the same code returned but it didn't set one for the other bank then that should rule out the sensor.

I gave the wiring information in my first post:

What you need to do is test for power on the red wire at the sensor connector when running. If ok then the yellow heater driver wire needs to be tested between the ECM and sensor for an open or short.

Customer: replied 1 month ago.
At the sensor, the harness wires are blue, white and 2 black wires, no red. The wire colors are identical on the OEM Toyota sensors and the Denso so I don't know where there is a red wire.
Expert:  sprinkles08 replied 1 month ago.

You're testing the wiring in the harness, you're not concerned with the wiring on the sensor itself.

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