"Raul" <alpesh.patel@gmail.com> wrote
> My 94 Civic has the check engine light on. Mechanic says
> its the O2
> sensor, which sounds reasonable.

You should be able to get the code read at an Autozone at no
charge.

The code may indicate a problem with the O2 sensor, but this
does not mean it must be replaced. Are their symptoms of
rough running when the car is driven?

Your car certainly is old enough that the O2 sensor may be
failing.

> However, he says that the sensor is
> essentially melted onto the intake manifold, so that the
> IM needs to
> be replaced too.

The O2 sensor is mounted on the exhaust manifold. It
monitors the oxygen content of /exhaust/ gases and sends a
signal to the engine control system to maximize engine (fuel
burning) efficiency and minimize pollution.

Has your mechanic actually put a wrench to the sensor and
tried to remove it?

If it seems the sensor has failed, and if you are the least
bit handy, I would take off the exhaust manifold shield (and
maybe any other small interference of parts), soak the O2
sensor's threads as best I could with the penetrating oil
"PB Blaster" (around $5 a can at Autozone and Wal-Mart).
Then I'd borrow an O2 sensor wrench from Autozone (no
charge) and try to remove it. If you can remove it, you can
buy an OEM sensor online and replace it yourself.

Here's a drawing of the O2 sensor location:
http://www.hondaautomotiveparts.com/...NIFOLD+%281%29

Great and inexpensive OEM O2 sensors:
https://www.automedicsupply.com/

For most 1994 Civics, the sensor costs about $70 at this
site.