How to Fix A Faulty O2 Sensor/Heater on Honda CivicIf you get a engine warning light, get it checked ASAP. I had a faulty O2 Sensor showing and kept putting it off and nearly killed my car.
The problem first started when going to work one morning. The MIL light came on and wouldn't go out. The car drove fine, with no problems all the way to work. Coming home later that day, there was no MIL, so I thought it was a one-off and left it like that. Over the next week, it would intermittently come on, but with no adverse effects on the performance, until one morning when the car would not start.
On ignition, revs rose to about 3k, fell to 500, dropped off, and stalled. I started back up again, and revs fell to about 100, then slowly rose to about 600-700 and started to idle ok except for a bad misfire every second. Lightly revved engine (to about 3k), the revs dropped to about 50 (nearly touching the pin); the whole car shook before the revs rose again to normal idle.
I checked all my spark plugs and wires and the vacuum lines but could not find anything wrong. The car was serviced only two months prior. At this point, I decided to find out what the ECU thought the problem was by checking the Diagnostic Trouble Code, which I found to be Error 41 - Primary Heated Oxygen Circuit, Circuit Malfunction. Driving over to my garage to get the pros to look at it, it cut out on me three times (while stopping at junctions, revs went down to nearly zero and stalled). They diagnosed the same problem and swapped out the whole sensor.
The ECU uses this sensor to calculate the air/fuel ratio, so it is no wonder why it kept cutting out!
