Anyone else dealing with this 12B701 error… what’s the fix?

Toyota Passenger and Sports Car Forums Supra
1

I keep getting a check engine light for this code: “12B701 - Oxygen sensor after catalytic converter, heating: Internal resistance too high.”

I put in an AA catted downpipe and tuned with MHD. At first, everything was fine, but after about a week, the CEL popped up. I cleared it, but it comes back every few days. I left it alone for over a month, and it never disappeared.

I reached out to AA, and they say it’s not an issue with the cat. Some people say it’s an O2 sensor issue, others say it’s not.

Anyone got a clear answer? This downpipe wasn’t cheap, and I got it to AVOID a check engine light.

Appreciate any help!

2

Try swapping out the oxygen sensor. Also, double-check that it’s installed correctly and not loose.

3

Hale said:
Try swapping out the oxygen sensor. Also, double-check that it’s installed correctly and not loose.

It’s not the O2 sensor. I replaced mine, and the problem didn’t go away.

4

My AA catted downpipe threw codes after two years. Could be something similar.

5

I have the same issue, and it’s driving me nuts. MHD support is useless. They just blame my setup, but this only started happening after I tuned it.

I’ve seen a few other people mention this too, so it’s not just us.

6

Running MHD with an AA catted downpipe here too. No issues so far, but I’ll keep an eye on it. Had the downpipe for years with no CEL, would be frustrating if the tune suddenly triggered one.

7

Same issue here, and no fix yet. I usually notice it when I push the car before it’s fully warmed up. You could try replacing the O2 sensor just in case. Make sure there are no leaks first. If everything checks out and AA isn’t helping, maybe ask your tuner if they can code it out.

8

I’d start by checking the install. Make sure everything is tight and nothing got on the sensor during installation.

9

Try swapping the stock downpipe back in and see if the code still comes up.

10

It’s probably the aftermarket downpipe. Did you select the aftermarket DP option in the Configure Flash Options menu?