How to test an O2 sensor?
Thread Starter
Burning Brakes
Joined: May 2000
Posts: 958
Likes: 0
From: Brisbane, Australia 1985 Coupe
How to test an O2 sensor?
Can anyone shed some light on how to test an O2 sensor? I know you measure the resistance but what is the range?
Just tracking the cause of my poor mileage.
:cheers:
Just tracking the cause of my poor mileage.
:cheers:
Burning Brakes
Joined: Dec 2002
Posts: 1,199
Likes: 4
From: Cairns Australia
Re: How to test an O2 sensor? (Chris O')
Hi Chris, this is funny because you just replied to my question on the NSW forum and here I am replying to you on the CF.
I recently fitted a heated O2 sensor to my 88. I took power from the fuel pump relay as that is only activated when the engine is running. My old sensor had had it, covered in deposits and also we discovered it was falling out of the exhaust pipe- yet it still didn't throw a code. My theory is that they work in such a harsh enviroment that the paramaters are too huge for any useful monitoring.
Ben 73 on the NSW Forum has some data on what resistance measurements you might expect, and perhaps one of the Guru's here will chip in with some numbers but basically I'd say fit a new one if yours has done more than 30 -50,000miles. You can use a Holden or Ford one as they all measure the same way.
My fuel useage was between 19 and 22 town driving with lots of stops. Thats Litres per 100Kilometres.
Now I am between 17 and 18 - still have to get the chip burnt to fully use the heated aspect of the sensor - then it will come out of closed loop earlier.
Hope this helps,
S'nut
I recently fitted a heated O2 sensor to my 88. I took power from the fuel pump relay as that is only activated when the engine is running. My old sensor had had it, covered in deposits and also we discovered it was falling out of the exhaust pipe- yet it still didn't throw a code. My theory is that they work in such a harsh enviroment that the paramaters are too huge for any useful monitoring.
Ben 73 on the NSW Forum has some data on what resistance measurements you might expect, and perhaps one of the Guru's here will chip in with some numbers but basically I'd say fit a new one if yours has done more than 30 -50,000miles. You can use a Holden or Ford one as they all measure the same way.
My fuel useage was between 19 and 22 town driving with lots of stops. Thats Litres per 100Kilometres.
Now I am between 17 and 18 - still have to get the chip burnt to fully use the heated aspect of the sensor - then it will come out of closed loop earlier.
Hope this helps,
S'nut
Former Vendor
Joined: Jun 2001
Posts: 7,204
Likes: 6
From: St Marys PA
Re: How to test an O2 sensor? (Chris O')
Drop the computer (ECM) down out. Locate the pin that corresponds to the 02 sensor wire. Attach a digital volt meter to the wire as close to the ECM as possible. Attach the other lead to a good ground. Start the car and observe the 02 readings in .xxx volts mode. You should see the readings go from .200 - .900 volts once the car is to temp. If the readings are steady or vary just a little then your 02 is likely bad. Replace it and re-observe the readings. If they are still lazy, you may need a heated 02, especially if when you give it gas it begins to vary as it should. This is telling you that there is not enough heat being generated ~650F to get the 02 sensor to perform its chemical reaction necessary to get a good reading.
If you replace the sensor, and the readings are still dead, even if you rev it, then you most likely have a bad wire. In which case it would probably be easier to just route and run a new one, eliminating the old. As trying to track down a shorted wire, could be a nightmare.
That should give you enough to be dangerous. :D :cheers:
If you replace the sensor, and the readings are still dead, even if you rev it, then you most likely have a bad wire. In which case it would probably be easier to just route and run a new one, eliminating the old. As trying to track down a shorted wire, could be a nightmare.
That should give you enough to be dangerous. :D :cheers:
Thread Starter
Burning Brakes
Joined: May 2000
Posts: 958
Likes: 0
From: Brisbane, Australia 1985 Coupe
Re: How to test an O2 sensor? (ski_dwn_it)
Thanks fellas.
Are all O2 sensors the same? What is the diff between heated and non heated? Do our ECM's work off heated O2 sensors?
:cheers:
Are all O2 sensors the same? What is the diff between heated and non heated? Do our ECM's work off heated O2 sensors?
:cheers:
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: How to test an O2 sensor? (Chris O')
Chris O', a heated O2 sensor works like a stock unit except that it also has two leads to supply power to heat it to operating temp (~300deg C).
So, the ECM will work with a heated one the same as a stock unit.
I don't know if they are all the same; if needed, you should get one for your car.
Instead of measuring the voltage, use the ECM's field test mode described on my site top see if the ECM goes into and stays in closed loop mode. If not you can suspect either the O2 sensor or the coolant temp sensor.
So, the ECM will work with a heated one the same as a stock unit.
I don't know if they are all the same; if needed, you should get one for your car.
Instead of measuring the voltage, use the ECM's field test mode described on my site top see if the ECM goes into and stays in closed loop mode. If not you can suspect either the O2 sensor or the coolant temp sensor.
Burning Brakes
Joined: Dec 2002
Posts: 1,199
Likes: 4
From: Cairns Australia
Re: How to test an O2 sensor? (65Z01)
I agree with DON M.
Mine was completely caked and obviously working very impaired yet my ECM went into closed loop. As I said, I believe the parameters for calling a fault code are so far apart that a wire has to come off or it almost falls off the car to set a code.
I fitted a Ford heated sensor, Aus$110 from Repco for my 1988 but according to Ben they are all the same and he has one on his 1984. (Repco part number ROX207.
I put a 3 amp inline fuse in the heater wire, the fuel relay uses a 10amp so I hope if anything shorts out it will just blow the 3amp and leave me with fuel. In fact I doubt that I would even know that the fuse had blown. It drew less than 1.5amps on startup and after 90 seconds or less was at about .8 of an amp.
Buy a new one, do it, go on, you know you wanna.
S'nut
Mine was completely caked and obviously working very impaired yet my ECM went into closed loop. As I said, I believe the parameters for calling a fault code are so far apart that a wire has to come off or it almost falls off the car to set a code.
I fitted a Ford heated sensor, Aus$110 from Repco for my 1988 but according to Ben they are all the same and he has one on his 1984. (Repco part number ROX207.
I put a 3 amp inline fuse in the heater wire, the fuel relay uses a 10amp so I hope if anything shorts out it will just blow the 3amp and leave me with fuel. In fact I doubt that I would even know that the fuse had blown. It drew less than 1.5amps on startup and after 90 seconds or less was at about .8 of an amp.
Buy a new one, do it, go on, you know you wanna.
S'nut
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Instructor
Joined: Aug 2003
Posts: 107
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From: Aurora OH
Re: How to test an O2 sensor? (65Z01)
a heated O2 sensor works like a stock unit except that it also has two leads to supply power to heat it to operating temp (~300deg C).
So, the ECM will work with a heated one the same as a stock unit.
So, the ECM will work with a heated one the same as a stock unit.
Thread Starter
Burning Brakes
Joined: May 2000
Posts: 958
Likes: 0
From: Brisbane, Australia 1985 Coupe
Re: How to test an O2 sensor? (Spinman)
What is the benefit of heating the O2 sensor to operating temperature quicker than it would reach during normal operations? Performance? MPG? Other?
To reduce warmup time before it begins to operate correctly and to reduce the possiblity of the sensor getting too cool at idle and forcing the ecm into open loop.
Thank guys! :thumbs:
