P0051 and 31 after headers installed.

[BioHAzard050]

Allright folks, need some guidance here. I just had some thorley headers dropped in my 05 V8, aka the Yank. Now, the headers are great, big gain in power and a boost in MPG. One issue though, both AF sensors are tossing a bad heater circuit code. Ive looked at both and the seem fine from the outside, both are connected. So far Ive checked the fuse, it was fine, dropped in a spare anyway. No dice. Switched the AF heater relay with the fog light relay (same part for both) to no avail. Before I start pricing out new sensors, what do yall suggest checking? Worst case scenario I swap one sensor and see if that sides code goes away.

 

[blackoutt]

Heater circuit faults often mean that the heater (little resistor heating element) is bad and have no effect on air fuel ratio other than the sensor must be within a certain temp range to work properly. Normally you can test the heater circuit for proper resistance at a given temp but I do not know what resistance spec would be or what pins to check. Is it possible that they got fried when headers were being welded on? The other common cause of heater circuit failure is poor O2 sensor placement or incorrect orientation causing water/condensation droplets to hit the sensor during it's start up warm up cycle and suffers from thermal shock. Sorry I couldn't help more, just what I know about O2 sensors.

 

[Brokeazzlos]

O2 sensors are bad if you have a heater code.

 

[BioHAzard050]

Yeah, I think they got toasted. Neither me nor the shop that installed the headers are particularly happy with the muffler shop that did the welding. Messy welds and by the looks of it, they left the damn sensors in when doing it. :mmph:

 

[BioHAzard050]

Can I get a part number for Densos? Not 100% sure the system at work (autozone) has the right one listed, would not be the first time.

 

[MT Runner]

Reviving an old one here. I have a little different situation and setup, but the same code.
I’ve contacted URD, just waiting to hear back, so hopefully I’ll have a good answer direct from them here soon.

I had the URD equal length headers and their O2 sim installed today. I have the P0051 code popping up. I can clear it with my scangauge but it pops right back up about 10 seconds later.

Could this be from the O2 sim being either bad or installed incorrectly?
Or could it just actually be a bad O2 sensor in Bank 1?

 

[blackoutt]

P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

This is the upstream sensor for a/f ratio, your O2 sim shouldn't be wired to anything to do with sensor 1 of either bank. This fault is for heater circuit on the passenger side header mounted O2 sensor. Do you have plug n play O2 sim? Should be installed on REAR O2 sensors, bank 1 sensor 2 and bank 2 sensor 2. If installed correctly then most likely back bank 2 sensor 1 heater, you can measure the resistance of the heater circuit to see if there is even continuity. Possibly just a bunged pin or plug not clipped all the way as well.

 

[MT Runner]

P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

This is the upstream sensor for a/f ratio, your O2 sim shouldn't be wired to anything to do with sensor 1 of either bank. This fault is for heater circuit on the passenger side header mounted O2 sensor. Do you have plug n play O2 sim? Should be installed on REAR O2 sensors, bank 1 sensor 2 and bank 2 sensor 2. If installed correctly then most likely back bank 2 sensor 1 heater, you can measure the resistance of the heater circuit to see if there is even continuity. Possibly just a bunged pin or plug not clipped all the way as well.

I have the plug and play O2 sim. The directions are specific and says to plug into rear O2’s. I double checked with the shop and they insisted that’s what they did, but I haven’t had a chance to look myself yet.

I know the code is officially for one of the front sensors, but the nature of this O2 simulator is that it tells the computer that the fronts are still reading properly, so I figured it could just be a bad O2 sim altogether or plugged in wrong if it’s throwing a code for a front sensor.

I’m not mechanically inept by any means but I’ll be the first one to admit that this is out of my element and not something I’ve dealt with before, so I’m looking for any advice in trouble shooting.

I suppose I can start by making sure that everything is plugged in securely, then I can always see if I can flip the plugs around in case they’re plugged in to the wrong sides.

 

[blackoutt]

I have the plug and play O2 sim. The directions are specific and says to plug into rear O2’s. I double checked with the shop and they insisted that’s what they did, but I haven’t had a chance to look myself yet.

I know the code is officially for one of the front sensors, but the nature of this O2 simulator is that it tells the computer that the fronts are still reading properly, so I figured it could just be a bad O2 sim altogether or plugged in wrong if it’s throwing a code for a front sensor.

I’m not mechanically inept by any means but I’ll be the first one to admit that this is out of my element and not something I’ve dealt with before, so I’m looking for any advice in trouble shooting.

I suppose I can start by making sure that everything is plugged in securely, then I can always see if I can flip the plugs around in case they’re plugged in to the wrong sides.

The O2 simulator tells the rear sensors that they are still reading a signal as if there were a catalyst installed. O2 sim or not, catalysts or not, the front "O2" which are actually A/F ratio sensors (using more than 0-1v) do not care what the rear sensors say. The rear sensors are only there for emissions to let you know when you catalyst has gone bad or missing so since you went to no cat in the headers any longer you have to trick it.

So back to the fault code, there are two circuits in an O2 sensor, one is for the O2 sensor feedback - a voltage value driven by oxygen content in the exhaust stream. The second is a heater element. Your fault code is for the heater element. It's possible to damage the heater removing/installing an old sensor or with a pin/plug pushed back or not clipped completely. As mentioned you can use a multimeter to measure resistance of the heater circuit to see if it open or shorted (replace sensor) or reasonable resistance (look at other wiring).

 

[MT Runner]

The O2 simulator tells the rear sensors that they are still reading a signal as if there were a catalyst installed. O2 sim or not, catalysts or not, the front "O2" which are actually A/F ratio sensors (using more than 0-1v) do not care what the rear sensors say. The rear sensors are only there for emissions to let you know when you catalyst has gone bad or missing so since you went to no cat in the headers any longer you have to trick it.

So back to the fault code, there are two circuits in an O2 sensor, one is for the O2 sensor feedback - a voltage value driven by oxygen content in the exhaust stream. The second is a heater element. Your fault code is for the heater element. It's possible to damage the heater removing/installing an old sensor or with a pin/plug pushed back or not clipped completely. As mentioned you can use a multimeter to measure resistance of the heater circuit to see if it open or shorted (replace sensor) or reasonable resistance (look at other wiring).

Gotcha, that makes sense. Thank you

 

[MT Runner]

So this ended up being frustratingly simple.

I was able to get under the 4Runner yesterday, I was going to check all the connections to make sure everything was snug.
The issue was very obvious, the first O2 sensor was in the header, but the plug was not plugged in, it was just dangling there.

I couldn’t quite reach it myself so I brought it back to the shop today. They plugged it in and the check engine light is off now. All is good.

 

[rdruss]

Kinda problems we like!