355 OBD2 codes P1117 and P1121

I know that these codes are for the heating element in the post-cat O2 sensors, left and right.

Problem is, I've replaced both O2 sensors; in fact, all 4 sensors (pre-cat and post-cat) have been replaced with new sensors. These are new codes after the replacement of all sensors.

The codes come up as pending codes quite quickly after clearing codes, and this behavior can be repeated. I've even tried disconnecting the battery, waiting overnight, reconnecting, getting the car up to temp, and then doing the 10 minute ECU learn procedure. The pending codes will be there after the idle session.

And, I've even driven the car, hoping they are just spurious pending codes, but eventually the Check Engine light turns on with these codes set.

Any ideas? What's the next thing to try? Could the cats be bad? (No Slow Down lights have come on) Could I have gotten two bad O2 sensors? (odds seem unlikely)

 

O2 sensors were replaced because there were other codes for the O2 sensors before. When I get O2 sensor codes, I like to replace all 4 O2 sensors.

As for the pending/set codes: The codes are pending almost immediately after an erase. However, after drive cycles, eventually the CEL turns on and the codes are actually set (not pending).

I did check the fuses for the O2 sensors (heating circuits), and can you believe this? The RH side fuse was MISSING.

Fuse was replaced. Hopes were high. Let it idle for 10 minutes. Same result: P1117 and P1121.

I got some offline advice that one of the thermocouple ECUs might be bad. So, I'm swapping ECUs from a known good car into this one, and I'll report the result.

 

O2 sensors are correct parts, and I have verified that each one is plugged in to the correct connector.

I will check voltage and resistance next, after trying a swap of the thermocouple ECUs.

 

As johnk predicted, thermocouple ECUs did not have any effect.

 

Don't know, will look. Why would that make a difference?

 

I've confirmed that everything is wired correctly. All of the part numbers are correct. Electrical connections are clean and test correctly.

There _are_ high-flow cats on this car. O2 sensor extenders were installed, and the codes do not return.

Of course, now, I have to drive the car for a while, but it looks like the problem is hopefully solved!

I owe all of you a virtual beer, or a real one if you come down to Houston... Thanks for everyone's help. What a great community.

 

Yes. Other than installing new O2 sensors, which caused the P1117 and P1121 codes, the only thing that I changed was adding the extenders to the post-cat O2 sensors.

 

Maybe. However, there were different codes before I replaced the O2 sensors, indicating that the sensors themselves were the problem.

P1117 and P1121 only occurred after the O2 sensors were all changed.