oxygen sensor

Shilton · Mar 6th, 2006, 17:45

Now as the weather is milder (down south anyway) I tackled replacing the oxygen sensor that was intermitintly putting the emission warning light on. I replaced it with a generic one, (I know you get what you pay for) and I soldered all the joints but still , I get the warning light coming on? I have put a meter on it and it is hard to determin if the voltage is cycling at all. The fault light comes again after clearing the fault codes when slowing down with just the foot of the accelerator this happens 3 times a day to once a week the longest without the light is 5 weeks . I have no problems with running and the fuel consumption is the same with the light on as off. It passed the m.o.t with the light on with no problem. Can this fault be ignored?

Mike_Brace · Mar 7th, 2006, 10:01

You haven't said what the fault codes are. My guess is it is almost certainly overfuelling in the circumstances you describe. If the fault is only occurring for a few seconds the light can probably be ignored although over fuelling does risk damage to the cat if it is continual. When light stays on you have no means of knowing if other faults happening.
Short term it is ok to ignore. Let us know what your codes are.

Mike

Peter D · Mar 7th, 2006, 10:49

What tpye of meter. You can use a very high input resistance digital meter but mot a moving coil type. What if any voltage did you get and what fault codes. Regards Peter

Shilton · Mar 7th, 2006, 18:02

In answer to Mike the fault code comes up with 2-1-2 no others and if it is over fueling where do I go to correct that fault
In answer to Peter I am using a digital meter.

With the original oxygen sensor I must admit in a moment of frustration I gave it a wack with a spanner and consquently it didn't bring up a light for 5-6 weeks not very scientific but I have always thought 'that when in doubt give it a clout' is a good thing to do when you dont understand what is going on. This may be that it cleared the deposits from the sensor but does'nt explain the new sensor ( Duff?) only working for the first 22 miles and believe me I canned the engine and used every gear to its max.

I have been in touch with the the 2 previous owners who both had it serviced by a reputable Volvo dealer in Guilford every year/6000 miles with the paper work to prove it and it always came out with a clean bill of health albeit that the bulb to the warning light had blown (dodgy servicing?)

Peter D · Mar 7th, 2006, 20:40

Check to see if the heater is working, the one in the sensor that is. Also check that the exhaust at the point where the sensor is is well earthed as this is a three wire sensor. Can you gain access to a scope. ?? You did not tell me what voltages you saw so how can I help. Regards Peter

Shilton · Mar 8th, 2006, 19:22

OK the voltages from the oxygen sensor was between 4.7v and 5.1v and I have got an open circuit on the heater. I assume that this means the sensor is knackered and working on a open loop and that I need a new one.

However if the e.c.u is working at a default value does this not mean that emissions are within workable perameters? and its not harming the engine?

And how does a one wire sensor produce a voltage?

Peter D · Mar 10th, 2006, 15:38

In open loop mode the voltage is 0.6 of a volt and operating the voltage cycles slowly 1/2 to 1 and a 1/2 seconds between 0.9 and 0.1 volts. how you get 4.7 volts I do not know. If the heater is us then it's new sensor time £40.00. Bit tight to get it out. Cut the cable and get a good ring round it. Ideally a Hex Ring rather that a Bi-Hex ring. Regards Peter

Mar 6th, 2006, 17:45	#1
Shilton Junior Member Last Online: Jun 5th, 2013 19:16 Join Date: Dec 2003 Location: london	oxygen sensor Now as the weather is milder (down south anyway) I tackled replacing the oxygen sensor that was intermitintly putting the emission warning light on. I replaced it with a generic one, (I know you get what you pay for) and I soldered all the joints but still , I get the warning light coming on? I have put a meter on it and it is hard to determin if the voltage is cycling at all. The fault light comes again after clearing the fault codes when slowing down with just the foot of the accelerator this happens 3 times a day to once a week the longest without the light is 5 weeks . I have no problems with running and the fuel consumption is the same with the light on as off. It passed the m.o.t with the light on with no problem. Can this fault be ignored?

Mar 7th, 2006, 10:01	#2
Mike_Brace Former contributor Last Online: Jul 2nd, 2022 07:54 Join Date: Dec 2004 Location: Rhosgoch, Anglesey	You haven't said what the fault codes are. My guess is it is almost certainly overfuelling in the circumstances you describe. If the fault is only occurring for a few seconds the light can probably be ignored although over fuelling does risk damage to the cat if it is continual. When light stays on you have no means of knowing if other faults happening. Short term it is ok to ignore. Let us know what your codes are. Mike __________________ A Volvo is for life not just for Christmas!

Mar 7th, 2006, 10:49	#3
Peter D Peter D Last Online: Mar 2nd, 2015 21:03 Join Date: Dec 2002 Location: Livingston	What tpye of meter. You can use a very high input resistance digital meter but mot a moving coil type. What if any voltage did you get and what fault codes. Regards Peter

Mar 7th, 2006, 18:02	#4
Shilton Junior Member Last Online: Jun 5th, 2013 19:16 Join Date: Dec 2003 Location: london	In answer to Mike the fault code comes up with 2-1-2 no others and if it is over fueling where do I go to correct that fault In answer to Peter I am using a digital meter. With the original oxygen sensor I must admit in a moment of frustration I gave it a wack with a spanner and consquently it didn't bring up a light for 5-6 weeks not very scientific but I have always thought 'that when in doubt give it a clout' is a good thing to do when you dont understand what is going on. This may be that it cleared the deposits from the sensor but does'nt explain the new sensor ( Duff?) only working for the first 22 miles and believe me I canned the engine and used every gear to its max. I have been in touch with the the 2 previous owners who both had it serviced by a reputable Volvo dealer in Guilford every year/6000 miles with the paper work to prove it and it always came out with a clean bill of health albeit that the bulb to the warning light had blown (dodgy servicing?)

Mar 7th, 2006, 20:40	#5
Peter D Peter D Last Online: Mar 2nd, 2015 21:03 Join Date: Dec 2002 Location: Livingston	Check to see if the heater is working, the one in the sensor that is. Also check that the exhaust at the point where the sensor is is well earthed as this is a three wire sensor. Can you gain access to a scope. ?? You did not tell me what voltages you saw so how can I help. Regards Peter

Mar 8th, 2006, 19:22	#6
Shilton Junior Member Last Online: Jun 5th, 2013 19:16 Join Date: Dec 2003 Location: london	OK the voltages from the oxygen sensor was between 4.7v and 5.1v and I have got an open circuit on the heater. I assume that this means the sensor is knackered and working on a open loop and that I need a new one. However if the e.c.u is working at a default value does this not mean that emissions are within workable perameters? and its not harming the engine? And how does a one wire sensor produce a voltage?

Mar 10th, 2006, 15:38	#7
Peter D Peter D Last Online: Mar 2nd, 2015 21:03 Join Date: Dec 2002 Location: Livingston	In open loop mode the voltage is 0.6 of a volt and operating the voltage cycles slowly 1/2 to 1 and a 1/2 seconds between 0.9 and 0.1 volts. how you get 4.7 volts I do not know. If the heater is us then it's new sensor time £40.00. Bit tight to get it out. Cut the cable and get a good ring round it. Ideally a Hex Ring rather that a Bi-Hex ring. Regards Peter

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