<e30> re: Oxygen Sensor: Problem

[Christopher Pawlowicz <chrisp@xxxxxxxxxxxxxxx>]

Chris Baisley sez
>At highway speeds under heavier engine loads such as uphill grades, "CHECK
>ENGINE" lights up.  Light goes out if I lift off the throttle, comes back
>on when I accelerate.
>
>DME Code Readout:
>
>1221, which indicates an oxygen sensor problem.

ok, first question: when was O2 sensor last changed ?
if it's been on there for more than 60k miles, it is probably TOAST

>Test: voltage output of oxygen sensor, warm engine running at idle: varies
>from 0.08 to 0.55 volts

I'm pretty sure it should be oscillating up and down to almost 1V
(vary between 0 and 1 V instead of between 0 and .5 V)

>Test: resistance of oxygen sensor heater (engine warm): varying from 5.1
>ohms up to 10 ohms
>Conclusion: heater element is out of spec (should be less than 5 ohms),
>probable cause of problem.
>

I think the heater only used to initially warm up the sensor.. ie: when
engine is warm, heater makes no difference.

>Guidance and comments would be appreciated, before I drop $300 to $400 CDN
>(ouch!) on a new four wire sensor.  Are there other tests that I (or the
>dealer) could do prior to replacing the part?  Anybody know a cheaper
>source for the part in Canada?  (Bav Auto has 'em for $124.95 USD, which is
>probably better even with exchange to CDN and duty).

I'd say that 
a) if your O2 sensor is older than 60k miles it is probably dead
b) if the sensor only works at the bottom of it's range (0-.5 instead of 0-1V)
 it is probably dead
c) a 4 wire o2 sensor from Hott Rodd (among other aftermarket places) is
 $70 USD  ( http://www.allbmwparts.com/bmwpart/ )


The same sensors should be available in Canada.. I think I paid my mechanic
something like $150CDN (~ $100USD ) for a sensor which he spliced in..
worked fine, but even getting one from Rodd would be fine if you can't
find anything locally.


Chris Pawlowicz
'89 325i
'74 2002

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