Swapped out O2 sensors and getting P0031 and P0051

Hey fellas,

My GF and I swapped out both of her exhaust manifolds with the Dorman manifolds from Amazon, along with both Upstream O2 sensors (AFR). Figured, while we were in there, might as well do the O2 sensors. She bought Denso 234-4261 O2 sensors.

This is one of those relationship testing events. She did a lot of the work while I went to my job and cussed a LOT! She re-installed both manifolds and put all the nuts on them while I was at work. I'm not sure which part she hated the most - working with the tiny EGR connection at the rear of the manifolds or re-installing the lower factory skid plates. It was so satisfying to hear someone else cussing and throwing tools around for a change :eyebrows:

Trouble is, the 234-4261 sensors plug didn't mate up to the factory plug on the engine. Apparently, this is a hit/miss deal based on the Amazon reviews. The wire colors matched with the Toyota sensors - Black, Black, White, Blue. Some folks simply lop off the connector and swap them using butt splices. I took the more elegant solution, de-pinned both connectors and swapped. I took pics and made a note of which color wire goes into which port in the connector. It's really hard to mess this up but apparently I did!

Now she gets P0031 and P0051 - A/F sensor heater (bank 1 & 2) range check (low current).

I couldn't find an online manual for an '08 but did find one for '06 http://www.ezdries.net/Vidpics/4Run... Engine Control System/SFI System/0060016.pdf

I'm trying to reconcile the color codes from the Amazon O2 sensors to an EWD. I don't see an online 2008 4Runner 2UZ-FE EWD so I'm using my hardcopy of 2003 4Runner 2UZ-FE EWD. I'm making a huge assumption that the color codes for the O2 sensors haven't changed between the two model years. Someone please correct me if I'm wrong here.

On my 2003 4Runner 2UZ-FE EWD, I see the following terminals out of the ECM:

Term OX1A color: red - this is the Oxygen sensor feedback to the ECM
Term HT1A color: green - this is the O2 sensor heater wire from ECM
Term +B color: Blue w/ White stripe - battery power source from EFI fuse
Term E1 color: brown - this is GND

So, can someone tell me how do I match the above colors from the EWD to the Black, Black, Blue & White?

Using a DVM and a propane torch, this is what I determined:

Black wires are the heater wires. Resistance value changes based on how much I heat up the sensor tip. DVM is on Ohm setting
Blue wire is Positive voltage - DVM on DC volts
White wire is Neg voltage - DVM on DC volts

I'd like to use this knowledge to translate the wire colors.

My understanding has been that different O2 Sensor Part Numbers might be calibrated differently. I could be wrong (never got a definitive answer when I asked) but we've had parts in the past mistake one sensor for another and it causes codes that only the new correct sensor fixes (i.e. one that has the same connector but a 6" cable instead of a 3" one, otherwise they look identical).

That being said...

Not sure about the wire colours though I would imagine they stayed the same for the vehicle. Those DTCs usually indicate a short in the heater circuit, assuming the ECM and the wiring to the sensor is good.

Update-

The wiring colours, pin locations, and connector IDs for B1S2 & B2S2 Oxygen Sensors for the 2UZ-FE are the same across all model years. The B1S1 & B2S1 changed because pre-2005 they used Oxygen Sensors it seems.

Resistance Values for the AFR should be:

HT (Pin 1) to +B (Pin 2): 1.8 Ω to 3.4 Ω at 20°C (68°F)

HT (Pin 1) to AF- (Pin 4): 10 kΩ or higher

If they're not, the sensors are junk. The Relay Values for the AFR Heater Relay should be:

Pin 3 - Pin 5: 10 kΩ or higher
Pin 3 - PIn 5: Below 1 Ω (when battery voltage applied to terminals 1 and 2)

Post Note-

Wait are you having issues with the connector on the AFR Sensors or the Rear O2 Sensors? P0031 & P0051 are for the AFR Sensors (B1S1 & B2S1), I can't tell from your picture? Because the 2003 (at least according to the EWD) didn't have AFRs they used 4 Oxygen sensors, the pinouts are the same (the wiring colours are different); but now I'm wondering if you have the correct sensor installed.

Your Upstream (Air Fuel Ratio Sensor) should be a Denso 234-9051 if your using your Amazon obtained parts.

BlackWorksInc said:

Wait are you having issues with the connector on the AFR Sensors or the Rear O2 Sensors? P0031 & P0051 are for the AFR Sensors (B1S1 & B2S1), I can't tell from your picture? Because the 2003 (at least according to the EWD) didn't have AFRs they used 4 Oxygen sensors, the pinouts are the same (the wiring colours are different); but now I'm wondering if you have the correct sensor installed.

Your Upstream (Air Fuel Ratio Sensor) should be a Denso 234-9051 if your using your Amazon obtained parts.

Click to expand...

Yes, I'm having issues with the AFR sensors, we swapped out the exhaust manifolds so these sensors were swapped out. The #s you posted below match the #s I linked above for an '06 so it's good to know at least I can use an '06 FSM EWD for her '08. However, I can't find an '08 EWD online. Can anyone give me a link to an '08 or '06 EWD?

Unfortunately, without knowing what color wires are suppose to be pin 1,2,3,4 on the new sensor, the info below is hard to work with. That's where I'm stuck, how do I equate black, black, blue and white wires to the colors shown on the EWD. I need to know what color is AF-, B+, AF-, Heater. Assuming I can find an '08 EWD that shows the color. I have a hardcopy EWD for '03 but that's not compatible with an '08 EWD.

Resistance Values for the AFR should be:
HT (Pin 1) to +B (Pin 2): 1.8 Ω to 3.4 Ω at 20°C (68°F)
HT (Pin 1) to AF- (Pin 4): 10 kΩ or higher
If they're not, the sensors are junk.

The Relay Values for the AFR Heater Relay should be:
Pin 3 - Pin 5: 10 kΩ or higher
Pin 3 - PIn 5: Below 1 Ω (when battery voltage applied to terminals 1 and 2)

alia176 said:

Yes, I'm having issues with the AFR sensors, we swapped out the exhaust manifolds so these sensors were swapped out. The #s you posted below match the #s I linked above for an '06 so it's good to know at least I can use an '06 FSM EWD for her '08. However, I can't find an '08 EWD online. Can anyone give me a link to an '08 or '06 EWD?

Unfortunately, without knowing what color wires are suppose to be pin 1,2,3,4 on the new sensor, the info below is hard to work with. That's where I'm stuck, how do I equate black, black, blue and white wires to the colors shown on the EWD. I need to know what color is AF-, B+, AF-, Heater. Assuming I can find an '08 EWD that shows the color. I have a hardcopy EWD for '03 but that's not compatible with an '08 EWD.

Resistance Values for the AFR should be:
HT (Pin 1) to +B (Pin 2): 1.8 Ω to 3.4 Ω at 20°C (68°F)
HT (Pin 1) to AF- (Pin 4): 10 kΩ or higher
If they're not, the sensors are junk.

The Relay Values for the AFR Heater Relay should be:
Pin 3 - Pin 5: 10 kΩ or higher
Pin 3 - PIn 5: Below 1 Ω (when battery voltage applied to terminals 1 and 2)

Click to expand...

AFR B1S1:

Pin#1 [HT] (Red w/ Blue)
Pin#2 [+B] (White)
Pin#3 [AF+] (Yellow)
Pin#4 [AF-] (Brown)

AFR B2S1:

Pin#1 [HT] (Black w/ White)
Pin#2 [+B] (White)
Pin#3 [AF+] (Pink)
Pin#4 [AF-] (Blue)

BlackWorksInc said:

AFR B1S1:

Pin#1 [HT] (Red w/ Blue)
Pin#2 [+B] (White)
Pin#3 [AF+] (Yellow)
Pin#4 [AF-] (Brown)

AFR B2S1:

Pin#1 [HT] (Black w/ White)
Pin#2 [+B] (White)
Pin#3 [AF+] (Pink)
Pin#4 [AF-] (Blue)

Click to expand...

This is good info, thanks. So, if this is the color of the front AFR sensors according to the EWD, any idea why do the AFR sensors on her vehicle have Black, Black, Blue and White color wires? Her sensors are the original Toyota AFR sensors.

alia176 said:

This is good info, thanks. So, if this is the color of the front AFR sensors according to the EWD, any idea why do the AFR sensors on her vehicle have Black, Black, Blue and White color wires? Her sensors are the original Toyota AFR sensors.

Click to expand...

The black, blue, and white are and have been standard for AFR/Oxygen sensors for a while now. If you look at the diagram you'll see that the coloured wires actually stop at the AFR connector, the blue/white/black is part of the sensor itself not the vehicle harness.

I imagine this is done because of standardization and thus multiple wire colors don't have to be used for production, just wire length when making sensors.

You are using the rear 02 sensors in place of AF sensors. Completely different. Reason the plugs were different.

In your first pic the top sensor is the AF sensor and the bottom the 02.

97hb said:

In your first pic the top sensor is the AF sensor and the bottom the 02.

Click to expand...

That's what I was thinking also... but I thought he said earlier that the numbers matched what I linked he should have been using, so I dunno...

BlackWorksInc said:

That's what I was thinking also... but I thought he said earlier that the numbers matched what I linked he should have been using, so I dunno...

Click to expand...

I think both of you guys are prolly right. When she bought the sensors from Amazon, I think she bought O2 sensors and not AFR sensors. Hence, they don't fit the connectors.

We tried multiple pinout combo to no avail so we'll return to the original AFR sensors. What is troubling is that the EWD colors that BlackWorks laid out above do NOT match the AFR sensor (Toyota OEM) wire colors that we removed.

Still, no biggie, if we end up sending these back and getting the correct part that BlackWorks pointed out previously.

Removing the sensors from the manifold has been a PITA and we need a special tool like this one on Amazon https://www.amazon.com/Oxygen-Senso...1493222502&sr=8-13&keywords=o2+sensor+remover

When we dropped the manifolds previously, the sensors came with them and it was simple to remove them. But now that the manifolds are on the engine, dealing with the AFR sensors is a PITA.

Thanks again for all the inputs.

Help w/ P0051 Code (Bank 2 Sensors Already Replaced)

Hi there,

Similar to this issue, I have been struggling to fix a P0051 code on my 2005 SR5 (V6 / 4.0L). I recently failed emissions for high NOx, with the check engine light also being on.

I have replaced both Bank 2 sensors (Sensor 1 upstream of CAT and Sensor 2 downstream of CAT) and am still seeing the issue after clearing the code. The A/F relay and fuse also appear to be good, with no noticeable damage on the sensor wiring or pins.

When running diagnostics, I am seeing both upstream sensors (B1-S1 & B2-S1) fluctuating around 3.3 V nominal, which seem to be behaving normally. On the downstream sensors, B1-S2 seems to fluctuate within the 0.1 V to 0.9 V range I have seen called out on some of these threads, however, B2-S2 generally reads around 0.035 V, occasionally reaching up to 0.115 V.

I believe all the sensors are good, but it seems like there is an issue with the connection to the B2-S2 sensor based on the OBD data. As mentioned, the wiring looked good so I'd like to check the voltage at the ECM but am struggling to find a good pin-out to identify which pins I should be checking for B2-S2. Does anybody have a good diagram or photo to help understand?

Any other thoughts on how to solve this problem would be greatly appreciated.

Thanks,
Ryan

[email protected] said:

Hi there,

Similar to this issue, I have been struggling to fix a P0051 code on my 2005 SR5 (V6 / 4.0L). I recently failed emissions for high NOx, with the check engine light also being on.

I have replaced both Bank 2 sensors (Sensor 1 upstream of CAT and Sensor 2 downstream of CAT) and am still seeing the issue after clearing the code. The A/F relay and fuse also appear to be good, with no noticeable damage on the sensor wiring or pins.

When running diagnostics, I am seeing both upstream sensors (B1-S1 & B2-S1) fluctuating around 3.3 V nominal, which seem to be behaving normally. On the downstream sensors, B1-S2 seems to fluctuate within the 0.1 V to 0.9 V range I have seen called out on some of these threads, however, B2-S2 generally reads around 0.035 V, occasionally reaching up to 0.115 V.

I believe all the sensors are good, but it seems like there is an issue with the connection to the B2-S2 sensor based on the OBD data. As mentioned, the wiring looked good so I'd like to check the voltage at the ECM but am struggling to find a good pin-out to identify which pins I should be checking for B2-S2. Does anybody have a good diagram or photo to help understand?

Any other thoughts on how to solve this problem would be greatly appreciated.

Thanks,
Ryan

Click to expand...

Get the Torque app and see what your LTFT & STFT (long and short term fuel trims) and graph it. Compare them to what YouTube says and see if something is noticeable.

Googled says:

What the P0051 code means. This code is set when the car's computer, or Engine Control Module (ECM), detects low system voltage in the heater control circuit. Specifically, the code is referencing Bank 2 Sensor 1

The heater circuit is fault, interesting. So, I'm curious why the heater circuit isn't getting the proper voltage from the ECU?