Yes, the downstream sensor does affect fuel trim. At $57.79+shipping,
I'd just swap it out with a Bosch planar -- and nothing less. I
wouldn't use OEM Densos here. The Bosch universal type (#15733)
requires splicing the old connector on there, but it's easy to do IMO;
otherwise get one with a connector for $20 more.
The catalytic converter is basically a ceramic honeycomb coated with
platinum. It's usually the victim and not the villain. So before
replacing it (it's too late in your case but for others), I'd make
sure the engine is properly tuned up, no internal oil/coolant leaks,
timing belt and valve clearance should be correct etc. Make sure there
are no vacuum leaks. Make sure there are no exhaust leaks upstream of
the sensors/converter.
So swap out the downstream with a Bosch planar (not any cheap thimble
type). I hpoe that converter is still under warranty?
BOSCH Part # 15733 $57.79+shipping
www.rockauto.com
NGK Iridium-IX or Laser-Iridium spark plugs
www.ngksparkplugs.com
Bosch planar type sensor:
http://www.boschautoparts.com/Products/OxygenSensors/PlanarO2.htm
On Feb 19, 9:54 am, oparr <op... DeleteThis @hotmail.com> wrote:
> CEL came on the other day and the corresponding code is P0420
> (Catalyst efficiency below threshold (bank 1)). Cleared code so CEL is
> now off. Mileage is 148,000. Upstream sensor was changed 20,000 miles
> ago (heater went), still have original downstream sensor. Midas
> indirectly changed the catalytic converter back in September (blown
> silencer on that section of exhaust pipe).
>
> I've narrowed the list of usual suspects down to a faulty downstream
> sensor or flaky new converter. Based on cost, should I have the sensor
> checked/replaced or have tailpipe emissions checked first? Or should I
> take the car back to Midas and let them figure it out? Finally, is the
> downstream sensor part of the closed loop emissions setup or is just
> monitoring the converter its sole purpose? Thanks.
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