I have a 1996 Plymouth Grand Voyager SE with a 3.3L. The check engine light has intermittently come on. Some times it will remain lit for the entire time that the engine is running, other times it won't light for a month. The key on-off method displays a code 21, which according to my manual is the O2 sensor. Is there any way of telling if it's the upper or lower sensor, without spending $150.00 for both?
I've had the same thing going on for a couple months now, same vehicle too. It will stay off for a couple weeks and then back on again for a couple days. I purchased an Actron OBD II scanner, read the codes, and found out it is the upstream sensor. Rather difficult to get to, probably have to pull the intake manifold. I'm waiting for cooler weather before I attempt that. Maybe you know someone who has a scanner you could borrow, or pull in to Autozone or Checker and get a free scan. Also, haven't had much luck in finding a proper tool to remove/replace the device. The upstream sensor sits in a hollow on top of the exhaust manifold junction where you can't get a wrench on it so you need one of those special sockets with a cut-away to clear the wiring. I can't find one long enough to accept the size of this new Bosch O2 sensor.
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