O2 Sensor Problems (1221 CEL Code)

[RobertK]

After trying to get everything squared away before the fall rally I still have a CEL error code 1221.

I've verified the that the O2 sensor heater relay is fine, the wiring is correct, and tried 2 brand new sensors. I also cleared the ECU, removed the O2 sensor from the exhaust bung and started the car then got a 1222 error (which is what it should do). This verifies that the ECU is getting a signal from the O2 sensor. As soon as I clear the ECU again, plug the O2 sensor back into the exhaust and start the car I get 1221 again.

I'm now leaning toward a fuel mixture problem but I cannot figure out if I'm running rich or lean or if the car doesn't like not having a catalytic converter.

The car idles and drives around great no matter if the engine is hot or cold. I've driven the car all over town with no issues just this stupid CEL.

[Uber E30]

Did you check the intake boot? If its leaking it can cause that code too.

[RobertK]

Boot is brand new, found out today that it is running a little rich.

[87-325ic]

shouldnt that throw the 1222 code though? not the 1221?
im suffering the same problem, and it seems that replacing exhaust/ cats is the reason behind all of this.. it is so damned annoying that 1221 code!

sorry to revive the dead.

[SamE30e]

1221 is heater relay right? Make sure that there is actually 12v at the sensor. I had the same problem and there was a break in the wire.

[hoveringuy]

I started getting a 1221 code when idling for more than 1/2 minute.

My wideband A/F was showing very lean idle at around 19-20. The ECU was trying to compensate but when it couldn't get it back to 14.7 it threw the CEL.

I used propane gas through a plastic tube to pin-point the problem to the back of the intake manifold.

The smoking gun was a deteriorated rubber cap on a vacuum connection.

Problem solved!