SES Light - Code P0155 - How to fix?

[RacerJ]

My car's had the SES light on for a long time, and I finally got it scanned last weekend and found out it had been throwing code P0155 - O2 Sensor Heater Circuit (cylinder bank 2, sensor 1).

Well I had changed the spark plugs and plug wires last weekend, and for some reason that had fixed whatever was wrong and cleared the SES light. As you might imagine, I was doing a happy dance. [img]graemlins/fluffy.gif[/img] So the light stayed off for a week, until last night it came on while I was driving down to my friend's house. I checked the plugs and wires this morning and everything looks good. I haven't done anything else to the car since last weekend.

Any ideas what's causing the problem? The car's idling more roughly than usual, but other than that there's nothing that looks out of the ordinary.

My big problem here is that I have to get my car smogged within the next 2 or 3 days. :( So any help ASAP would be appreciated.

Thanks guys,
-James

BTW- bank 2 sensor 1 is the passenger side header sensor, right?

[John_D.]

Heater circuit... The newer o2 sensors have a built-in heater (and the 2 extra wires). Sensors don't read accurately when cold. Until the exhaust heats it up to about 600 degrees, the pcm can't use it. So the heater gets it there quicker. Also while idling, the exhaust is cooler than when under a load. The sensor can give inaccurate readings while idling, without a heater. So the obd2 checks that the heater circuit looks ok, and tells you if it doesn't. Replacing the sensor is the only way to fix the heater, since it's inside the sensor.

I don't recall the banks off the top of my head, but I'm pretty sure it's been posted or is in the technical library section. I've heard shops say if they only replace one side, the car often comes back a couple of weeks later, and the other side needs to be done. So many of them do both sides while they're at it, instead of having the customer think they didn't do it right the first time.