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The warning lights on the dash came on( Engine, VSC Off, VSC Trac, Slipping )and I had my brother check the codes with his SnapOn scanner. The codes are P0031 Bank1/1 Heater control ckt low and the other is C1201 Engine control system fault. I think I have a bad sensor, either a wheel speed sensor or an oxygen sensor or a bad wire in the harness, maybe all three. This happened about a week after wheeling in the mud. I also had the whole front suspension apart replacing the struts before the wheeling trip. Also it went away for about 2 days when the outside temp was -5. Any input would help. Thanks
 

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The warning lights on the dash came on( Engine, VSC Off, VSC Trac, Slipping )and I had my brother check the codes with his SnapOn scanner. The codes are P0031 Bank1/1 Heater control ckt low and the other is C1201 Engine control system fault. I think I have a bad sensor, either a wheel speed sensor or an oxygen sensor or a bad wire in the harness, maybe all three. This happened about a week after wheeling in the mud. I also had the whole front suspension apart replacing the struts before the wheeling trip. Also it went away for about 2 days when the outside temp was -5. Any input would help. Thanks

disconnect battery for a minute or so and hook it back up and see if it helps.

had to do that once and it worked. same lights you mentioned I had issues with
 

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Discussion Starter #3
disconnect battery for a minute or so and hook it back up and see if it helps.

had to do that once and it worked. same lights you mentioned I had issues with
I tried that and it didn't work. They also came right back on after my brother cleared the codes. Something is definately wrong.
 

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are all the codes identified by your reader? some codes are only readable by dealer though I am sure someone here has them posted somewhere.
 

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The warning lights on the dash came on( Engine, VSC Off, VSC Trac, Slipping )and I had my brother check the codes with his SnapOn scanner. The codes are P0031 Bank1/1 Heater control ckt low and the other is C1201 Engine control system fault. I think I have a bad sensor, either a wheel speed sensor or an oxygen sensor or a bad wire in the harness, maybe all three. This happened about a week after wheeling in the mud. I also had the whole front suspension apart replacing the struts before the wheeling trip. Also it went away for about 2 days when the outside temp was -5. Any input would help. Thanks
P0031 is the oxygen sensor in front of the catalytic converter. The relay for the sensor could be bad, the sensor could be unplugged or the wire broken, the sensor could be bad, or (most unlikely) the ECM could be bad.

I don't think C1201 is a Toyota code, must be a Snap-on scanner code.
 

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Discussion Starter #6
Why would three different VSC lights turn on in the dash if it was just an oxygen sensor? I thought maybe the wire that suppies voltage to the oxygen sensor also supplies voltage to the wheel speed sensors, but I don't know. We were also able to read wheel speed from all four wheels. I'm puzzled.
 

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Why would three different VSC lights turn on in the dash if it was just an oxygen sensor? I thought maybe the wire that suppies voltage to the oxygen sensor also supplies voltage to the wheel speed sensors, but I don't know. We were also able to read wheel speed from all four wheels. I'm puzzled.
I don't know. They may not necessarily be related; you may have two separate issues coincidentally happening at the same time.

Since it happened after you were mudding, the first things I would look for would be disconnected, broken, or wet connectors to the wheel speed sensors and the oxygen sensors.
 

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Make sure your gas cap is on tight.
 

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For some reason on these vehicles, they decided to light up the dashboard like a christmas tree whenever there is a decent fault code instead of just tripping the 'check engine' idiot light. I have no idea why and haven't heard a good reason for it. Most everyone freaks the first time it happens.

DEWFPO
 

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Discussion Starter #10
I don't know. They may not necessarily be related; you may have two separate issues coincidentally happening at the same time.

Since it happened after you were mudding, the first things I would look for would be disconnected, broken, or wet connectors to the wheel speed sensors and the oxygen sensors.
:thinkerg:You got me thinking......I think I may have two separate issues. I didn't have the front aligned after I changed the front struts. That may be why the VSC lights are lit up. The VSC is possibly shut down because the sensor on the steering column is out of whack.
The other is probably an ox sensor.
I'll fix those things and post up if it worked
 

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I have had the same lights and according to the dealership my cats are gone. I have headers and they will not replace the cats. Cost through a SoCal dealer is around 4500 bucks so I went to URD and bought their little spacers and eliminated the light problem. I will replace with aftermarket cats when they are available in California.

Hopefully before smog is required in November.
 

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p0031 is a fairly common issue on current yota veh's typically it is a a/f sensor failure internal b1s1 befor the cat but may be a differnt issue such as damaged wireing etc, the outher code is a yota cod p1201 typically sets with many powertrain codes such as this, p1201 is nothin to worry about it will clear when the a/f sensor is repaired also any powertrain code also disables vsc,trac etc this is normall the reason for this is if the engine is having a drivabilty issue such as misfires atc the ecm cannot control the vsc, trac system properly the ecm does not know how the veh will respond to applying brake force to the wheels etc it may worsen ur skid etc or possibly further damage the powertrain depeding on the problem its having.
 

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no, you dont have two separate issues. that c1201 code always sets with CEL's.

active test the sensors and see if they are bad, if so, replace the one thats bad. or if they are responding, replace the cat.
 

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I have the same exact problem as of this morning :( Did you ever find the problem? I am going to have to take it to the dealer after work, that should be fun...
 

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no, you dont have two separate issues. that c1201 code always sets with CEL's.

active test the sensors and see if they are bad, if so, replace the one thats bad. or if they are responding, replace the cat.
Active test what? If it's a heater code for the sensor it's done. Simple continuity test will reveal if it's good or not.
 

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Discussion Starter #17
Thank you for all of the replies everyone. I still have not fixed it yet due to cold weather. I'm not fond of laying on my back in the snow. Its supposed to warm up this Saturday so I'd like to try and replace the sensor. I think b1s1 is located before the cat on the passenger side and the Denso part number is #234-9051. If my thoughts on location or part number is wrong please post up.
Thanks, Randy
 

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P0031 is the oxygen sensor in front of the catalytic converter. The relay for the sensor could be bad, the sensor could be unplugged or the wire broken, the sensor could be bad, or (most unlikely) the ECM could be bad.
I am having the same issue. I have the battery disconnected now to see if that works, if it doesn't, could you provide some guidance as to where in front of the cat the sensor is located? It's -9 degrees C here right now so I'd like to spend as much time inside the house as possible! lol

Thanks,

Steve
 

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Discussion Starter #19
It is fixed. I replaced the A/F O2 sensor with a Denso part and had my brother clear the codes with his Solus scanner. All of the warning lights on the dash turned off and stayed off. Two more things I learned (1) the lights won't go out until the codes are cleared from the ECM and (2) Amazon.com was the cheapest place to buy that part. I appreciate all of the replies from the forum members here. I would have probably taken it to the dealer if it wasn't for your help. Thanks guys.

-Randy
 

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I am having the same issue. I have the battery disconnected now to see if that works, if it doesn't, could you provide some guidance as to where in front of the cat the sensor is located? It's -9 degrees C here right now so I'd like to spend as much time inside the house as possible! lol

Thanks,

Steve
Sorry, I just your post right now. If it's not too late, the heated O2 sensors are located in bungs right in front of the cats proper, on the top side of the exhaust pipe-front of the cats, one on each side. The driver's side one is right behind the flange where that cat hooks into the down-pipe from the manifold on that side. The passenger side one is closer to the cat proper. You may have to remove the transmission-support frame cross-member to get at them very easily; I don't remember for sure because I don't have the stock frame cross-member any more.
 
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