Darned Oxygen Sensor, help appreciated

Alrighty, this 1997 Voyager 3.3 with 83K is really starting to nickle and dime me, service engine light retruns a 21...Oxygen Sensor.

I figure, I'll take a stab at wrenching this one myself.

I figure start on the forward, check the light see if it goes out, if not go and do the lower sensor as well.

Problem you ask? Where is the darn thing. I can see the lower but not the upper.

Chilton's refers to it when they describe replacing the manifold cover...they say, remove the accessory belt, remove the Alternater, remove the Oxy Sensor.

Is it really under the alternator?

I don't want to yank the alternator and still not be able to get at it and I can't see it at all from under the car.

Also, any "pitfalls" to expect? Asa far as I know it's a bolt in part, attach the wires and remount, no?

Any calibration or such?

My mechanic deserves every penny he's paid and then some but I have to save some money if I can.

Mine is a 4 cylinder, so it will be slightly different. You get to the front oxygen sensor from above. On the 4 cylinder (and probably the 6 cylinder), it becomes quite easy, once you remove the resonator chamber from the air intake (the thing that everybody thinks holds the air filter, until they can't get it apart, and then realize there is no fillter in there anyway). You DO need an oxygen sensor socket for the front one. They don't cost all that much - certainly less than paying a mechanic the labor.

BUT, replacing parts to make the check engine light go out is an expensive way to go. So of the major auto supply stores (like Autozone) will let you borrow a code reader. Plus they have gotten pretty cheap (around $99). It's worth owning one.

Thanks,

Yes, the set-up oon the six is different, hoping someone can come long that has a 6 and confirm that I'll be able to get a hold of the thing if the alternator comes off.

I have seen some reference from people going at it from below but I am not even able to see it from under, unless I am just looking in the wrong place...logically it shuold be right above the cat. converter.

There is an auto supply every 20 yards or so around here, should be no problem getting the socket.

Also I did receive the code 21 and have been told the first step in that case is to replace the O2 sensor...reccomended that both be changed but I figure at least try the top side first than the lower.

Am I missing something else that could be checked with a code 21?

Oxygen Sensor codes are P0131 through P0141. OBD-2 Code P0021 is "camshaft position timing overadvanced or system performance (Bank 2)". That's a pretty unlikely condition. If the timing belt had jumped a tooth, the cam timing would be retarded, not advanced.

Hex code 21 is "Engine is cold too long. Engine did not reach operating temperature within acceptable limits." (I.E. the thermostat is stuck open.) There is a note on this code that says that it will not light the check engine light. It says to check for it using the procedure below:

The check engine light can display trouble codes: "Cycle the ignition switch on, off, on, off, on, within 5 seconds and any diagnostic trouble codes stored in the PCM will be displayed."

The upstream sensor is in the top of the rear exhaust manifold. I access them from underneath, it is not a fun job. The sensor is directly behind the middle rear spark plug.

mprtech, thanks, that is right about where I figured it was.

jagplates, the proceedure you describe is how I accessed the codes...I got:

blink, pause blink, blink = 12 (battery recently disconnected)

Blink, Blink, pause Blink = 21 (list I was looking at had it as Oxy sensor)

blink, blink, blink, blink, blink pause blink, blink, blink, blink, blink = 55 (end of codes)

Did I interpret the codes incorrectly.

BTW, the light has been on and off for a couple weeks, stared staying steady on for the last 3 days or so but today is off again...all day with several start ups and 30-40 miles traveled.

Thanks again for the help.

http://www.robskorner.freehomepage.com/faqs/computercodes.html

Here is one list of the fault codes I have found, matches the list I referd to ...did I make an error?

I am using the online manual at www.alldatadiy.com. They make reference to:
MIL Code Number: nn
Hex Code Number: nn
Scan Tool Code Number: Pnnnn
but interestingly enough, they only seem to offer charts for the scan tool codes and Hex codes. I have to assume that the MIL code is the code that you extract from the MIL (Malfunction Indicator [check engine] Light).

Oxygen sensors should be replaced every 100,000 miles or so, so it couldn't hurt to replace them.