Yesterday my e30 started generating a persistant CEL (Check Engine Light) error 1221 which indicates the o2 sensor has failed or is sensing values so far out of spec it can’t be interpretted. I suspect that driving around with a nagging misfire for almost a month fouled the sensor. The sensor is only a couple months old, which is a shame. Thankfully I kept my old sensor which I’ll use until it fails or I finally swap in a s52 engine.

February 12, 2013 mechanical, repairs

Picked up a very reasonably priced and brand new o2 sensor. Took 5 minutes to install:

  1. locate the o2 sensor on the passenger side of the engine bay where it is screwed into the exhaust manifold
  2. spray it with some PB blaster and wait over night
  3. disconnect the o2 sensor from it’s harness
  4. because the o2 sensor is very close to the chasis you will not be able to use an o2 sensor wrench, instead use vise grips (push towards the firewall to loosen)
  5. remove the old o2 sensor
  6. manually thread the new sensor being careful not to get anti-seize compound on the tip
  7. you may have to flip the wiring harness around to keep it from getting twisted. tighten with the vise grips, turn towards radiator to tighten

The most important thing I learned was that all the commonly available o2 sensor wrenches will not work on the e30, but vise grips work perfectly. So I have 3 tools to return to Pepboys. I didn’t have access to the special BMW wrench but it’s hardly necessary.

This seems to have made no difference to how my car runs. Even though the old sensor was entirely encrusted in carbon and crud it was working fine or had no bearing on the car’s stalling, bogging and CEL.


Above: The new o2 sensor fitted to the exhaust manifold.

Part Numbers:

Oxygen Sensor, 325i/is/iC/iX (9/87-91) 11-78-1-734-393-M14

November 18, 2012 repairs