I need to buy a new o2 sensor for my 2001 2.5 and my car has a 5 wire sensor...the 4 wire units are much cheaper ...what is the extra benefit gained by having the 5th wire

just a guess, but probably heated... heated units need an extra wire, and are generally quite a bit more expensive. no they aren't interchange either.

I have tried to look on the internet for some better understanding, but to no avail...For example: My old VW Canadian vanagon has 2 wires while for the same year in the States they had a third wire for heat..but the purpose for the 4th and 5th wire in the subi still seems to puzzle me..I am further confused by the fact that since I buy all my parts thru the US, there is no cross reference or part number given by the US parts suppliers for a 5 wire O2 sensor for a 2.5 canadian subi..a 4 wire is no problem even with the same snap on connector...just maybe between the two countries the O2 sensors were different just a guess, but probably heated... heated units need an extra wire, and are generally quite a bit more expensive. no they aren't interchange either.

I was able to find the correct O2 from Napa in Michigan..the only parts place with the correct 5wire and snap on connector for $72..a very good price considering the other parts suppliers wanted any where from $360 downwards

Different sensor technology. In general:
-- 1 wire sensor is old-school, just a signal wire with the ground coming from the exhaust itself
-- 2 wire sensor added a separate ground wire for a cleaner signal
-- 3 wire sensors added a heater circuit and both the heater and signal share a ground
-- 4 wire sensors have been the norm for a while and you basically have 2 circuits -- 2 wires for the heater, and 2 wires for the signal (adds dedicated ground to the 3 wire)

Recently, there have been more 5-wire sensors which are actually wide-band type sensors (as opposed to a simple "rich/lean" switching sensor). These sensors utilize a pumping current and different control scheme than the "simpler" switching sensors which simply generate a voltage based on O2 content....

Basically, if you've got a 5-wire O2 your car is running a wideband front sensor and you need to replace it with a similar sensor...

I was able to find the correct O2 from Napa in Michigan..the only parts place with the correct 5wire and snap on connector for $72..a very good price considering the other parts suppliers wanted any where from $360 downwards

I can get the front o2 from the local dealer for $75. Did you ever check with your local dealer. The rear one is more expensive but can be had at Autozone for about $65-70 with the factory connector. Subaru wants about $120 for the rear one.
My 2000 RS has a wideband and is the same for all the RS's with MAP's and no MAF.

Yes I did check with my local dealer and that is where I got the subaru part number, which become very useful when getting the O2 from napa..napa brings up the wrong sensor when just giving the yr of the car Etc.(3 wire) ..when searching and useing the subaru pt # it comes up with the 5 wire one at half the price of the 3 wire...$75)..the local dealer wanted some $350 for the orginal part# and $148 for the upgraded part #...their local jobber quoted over $400....their must be a lot of profits made in the parts business...interesting enough Rockauto/importecparts/ and several other places did not carry the o2 sensor for an automatic outback, which represents most of the outbacks..manaul trannys are rare I can get the front o2 from the local dealer for $75. Did you ever check with your local dealer. The rear one is more expensive but can be had at Autozone for about $65-70 with the factory connector. Subaru wants about $120 for the rear one.
My 2000 RS has a wideband and is the same for all the RS's with MAP's and no MAF.

Different sensor technology. In general:
-- 1 wire sensor is old-school, just a signal wire with the ground coming from the exhaust itself
-- 2 wire sensor added a separate ground wire for a cleaner signal
-- 3 wire sensors added a heater circuit and both the heater and signal share a ground
-- 4 wire sensors have been the norm for a while and you basically have 2 circuits -- 2 wires for the heater, and 2 wires for the signal (adds dedicated ground to the 3 wire)

Recently, there have been more 5-wire sensors which are actually wide-band type sensors (as opposed to a simple "rich/lean" switching sensor). These sensors utilize a pumping current and different control scheme than the "simpler" switching sensors which simply generate a voltage based on O2 content....

Basically, if you've got a 5-wire O2 your car is running a wideband front sensor and you need to replace it with a similar sensor...

This isn't quite right.

The 2-wire sensor adds a lead for the heater circuit. Both the sensor & heater ground through the exhaust. (I haven't seen many of these used)

The 3-wire sensor adds a ground for the heater circuit. The sensor still grounds through the exhaust.

The 4-wire sensor adds a separate ground for the sensor. In this configuration, nothing grounds through the exhaust.


Josh

Yes I did check with my local dealer and that is where I got the subaru part number, which become very useful when getting the O2 from napa..napa brings up the wrong sensor when just giving the yr of the car Etc.(3 wire) ..when searching and useing the subaru pt # it comes up with the 5 wire one at half the price of the 3 wire...$75)..the local dealer wanted some $350 for the orginal part# and $148 for the upgraded part #...their local jobber quoted over $400....their must be a lot of profits made in the parts business...interesting enough Rockauto/importecparts/ and several other places did not carry the o2 sensor for an automatic outback, which represents most of the outbacks..manaul trannys are rare

Goto subaruparts.com for prices and parts. If they are going to charge you that much. I say report them to SOA. I have been lucky with the local parts people. I mention to them if their prices are way off and tell them I can get it cheaper at subaruparts.com (which is a Subaru dealer) or another dealer. They have dropped the price in the past.

Thankyou for the advice..Goto subaruparts.com for prices and parts. If they are going to charge you that much. I say report them to SOA. I have been lucky with the local parts people. I mention to them if their prices are way off and tell them I can get it cheaper at subaruparts.com (which is a Subaru dealer) or another dealer. They have dropped the price in the past.