O2 sensor question

Hi guys

I have a few questions regarding o2 sensors..

Is an upstream sensor different from a downstream sensor?

I know that they serve different purposes, example:

1. If I need to replace an o2 sensor in a vehicle that only uses one sensor, will a downstream sensor work without any problems? (Besides the connector and wire length being different)

2. If i need to replace an upstream sensor in a vehicle, will a downstream sensor work without any problems aswell?

I have seen that the prices of an upstream vs downstream differ quite abit on various vehicles and im sure that its not because of a different wire length or type of connector.

Another question (a kind of stupid one too)
A) A 3 wire sensor is grounded via the exhaust and has:
1 - heater wire
2 - heater wire
3 - signal wire

A 4 wire sensor has:
1 - heater wire
2 - heater wire
3 - signal wire
4 - ground wire

Question: Will a 4 wire sensor work properly on a car that uses a 3 wire sensor, if the ground wire from the 4 wire sensor is disconnected or bolted onto the chassis of the vehicle?

Also, whats you guys opinion on universal sensors?
(Back to the above questions) Do u get an upstream universal sensor and a downstream universal sensor or are they the same?

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I know guys who hate universal sensors, I've never had a come back from one.

Upstream and downstream zirconia sensors operate the same way. If you had an AFR upstream sensor (out wideband sensor), that is not the same as a zirconia sensor, and therefore not the same as the post cat sensor. So far, I'm unaware of any manufacturers using AFR sensor after the cat.

Hope that makes sense.

Ash03 wrote: I know that they serve different purposes, example:

1. If I need to replace an o2 sensor in a vehicle that only uses one sensor, will a downstream sensor work without any problems? (Besides the connector and wire length being different)

2. If i need to replace an upstream sensor in a vehicle, will a downstream sensor work without any problems aswell?

I have seen that the prices of an upstream vs downstream differ quite abit on various vehicles and im sure that its not because of a different wire length or type of connector.

It might work? :blink: I know that on most makes/models, one big difference between the upstream and downstream sensors is the amount of heater current draw. For example, an '08 Escape:



It's possible that you may end up with a functional sensor, but still get a heater circuit code because the computer doesn't like the current draw. Some cars monitor heater current, some don't, so that'd depend on the specific vehicle.

Question: Will a 4 wire sensor work properly on a car that uses a 3 wire sensor, if the ground wire from the 4 wire sensor is disconnected or bolted onto the chassis of the vehicle?

Again, possibly? I've honestly never seen anyone do this before! :lol: If you do this, I'd genuinely like to know if it works.

On the model that make up the majority of vehicles I see the upstream and downstream sensors are the same part number, but swapping random sensors in from other vehicles has a 50-50 chance of working even if they are both zirconia types.
Also there are also a few very special cases with narrow band Titania sensors upstream and Zirconnia downstream

Thanks for the replies guys, really appreciate the input..

Currently working on a 1998 Kia Sportage 2.0 16v..

The car had an issue where its not drivable, would just start up - idle for a second then stumble and die.

My biggest issue is, this car is an OBD1, it does not even have an engine check light or anything of that sort , and i dont have an OBD1 scanner..
Anyway i gave it a shot without reading codes:

The car seemed like it was being starved of fuel, so i pulled of the intake pipe and added a fuel source and bam! Runs fine.
So when i pulled off the intake pipe, i happened to have a look at the maf and it was completely broken. (No hotwire or anything of that sort to measure the air flow).. did an unplug test, made no difference.. ordered a new maf - will get it replaced.

Since the car ran with an alternative fuel source, i decided to check the o2 sensor.. I wasnt surprised to have seen the o2 wiring being cut and joined (somebody has already fitted a universal o2 sensor some time back)..
I dont own a scope, so i pulled out my dvom and ran a voltage check on the signal wire, and the o2 signal is fixed rich at 2v (tested with added fuel source and a forced vac leak - made no difference to the reading).

So, it makes sense that the ecu is reading a super rich mixture hence its reducing fuel so much that its making the car stumble and die.

The issue is that the dealer does not have stock of an o2 sensor for this vehicle because its "old", and the price is ridiculas, so i have no choice but to use a universal sensor.
Another issue is that most of the part stores nearby mostly sell 1, 2 and 4 wire universal sensors and this car uses a 3 wire sensor.
The cost is not bad though, R395 which is about 33USD or so.

The owner (a friend of mine) agreed to "experiment" on the car by trying to fit in a universal 4wire sensor lol..

Will post the results after i get a break to work on that car..

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Paul has video on KIA MAF ---- really worth watching before fitting an aftermarket MAF to one of these.

Tyler wrote: [quote="Ash03" post=15204
It might work? :blink: I know that on most makes/models, one big difference between the upstream and downstream sensors is the amount of heater current draw. For example, an '08 Escape:

It's possible that you may end up with a functional sensor, but still get a heater circuit code because the computer doesn't like the current draw. Some cars monitor heater current, some don't, so that'd depend on the specific vehicle.

I was unaware of that Tyler! Could it be due to duty cycle variation of the heaters between upstream and downstream, or those just straight power and ground when activated?

Andy.MacFadyen wrote: Paul has video on KIA MAF ---- really worth watching before fitting an aftermarket MAF to one of these.

Thanks, will look into that.. already bought an aftermarket maf though.. an original from the dealer is half the price of the car (not exaggerating)

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Ok so the final result:

Fitted in a universal 4wire o2 sensor (ground wire bolted onto chassis) with a new aftermarket maf..

Car seems perfect now with a super smooth idle, no overfueling, and my friend says the car has gained some power (probably running bad previously from a dead maf and faulty o2)..

Thanks for all the input guys

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Noah wrote: I was unaware of that Tyler! Could it be due to duty cycle variation of the heaters between upstream and downstream, or those just straight power and ground when activated?

I believe these are the result of a full field test, but I could be wrong! These numbers also fall in line with what I've come to expect from O2 heaters. I can double check these numbers later this week.

Ok so the final result:

Fitted in a universal 4wire o2 sensor (ground wire bolted onto chassis) with a new aftermarket maf..

Car seems perfect now with a super smooth idle, no overfueling, and my friend says the car has gained some power (probably running bad previously from a dead maf and faulty o2)..

Thanks for all the input guys

So it works! I bet your friend is pumped to have his Kia running right again.

Honestly, I'd never even considered using a universal sensor this way. Way to think outside the box.

Lol yeah buddy hes a happy chappy now

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Seriously, nice work. It's always gratifying when an idea works well.