O2 sensor low voltage causing check engine warning

[kerrin]

My 2004 VY check engine warning light keeps coming on (usually when backing off on the power). Holden with their Tech2 scanner have diagnosed the cause to be: "right O2 sensor low voltage". My fuel economy has also dropped to 12.1/100 (was 8.6/100 on a similar long distance trip)

The same thing happened late last year, and the O2 sensor was replaced. It's been trouble free until now.

One mechanic believed replacing my rattling catalytic converters with resonators would be the cause - but I'm not so sure as the O2 sensors are before the cats (now resonators), and also the left one has not faulted.

Any advise would be greatly appreciated.

 

[colgf]

Check your wiring to the oxy sensor for dirty connector or chafed wire , make sure your earth wire has a good earth signal on the oxy sensor connector plug using an ohmeter. Disconnect your battery for about 15 secs to clear the stored memory faults , (make sure you know your radio code though before you disconnect the battery. ) That should fix it.

 

[kerrin]

I took it in to a Holden dealer today as I couldn't see any obvious issues with the connections. The sensor isn't easy to get to on the right hand side - if only it had of been the left one..

They diagnosed the sensor to be faulty again, and have recommended a genuine replacement + 2 1/2 hours labour.

They said that the cause was most likely in fitting the third party sensor the wires had been cut, and this was bad because oxygen also travelled alone the line. (I don't believe for a second that oxygen travels along an electrical line - but didn't argue with the office girl.. suspect something went wrong with the translation of the tech's notes. )

She couldn't explain why the third party sensor worked fine for almost a year. I suspect either the sensor was of poor quality (you get what you pay for), or the old plug wasn't making a good connection any more.

The third party sensor came without a plug attached - I would think so that it was vehicle independent, and also cheaper to produce/stock.

Hopefully this one lasts longer than the last one - fortunately the genuine sensor comes with a 2 year or 15,000km warranty. Expensive exercise though.

 

[Piper]

LOL oxygen travelling through the wire? :hit: :rofl:

 

[Ozzie]

2.5 hours labor to unscrew the O2 secsor?
Mate do it yourself it will take 10 mins.

 

[kerrin]

I took it in this time because I was concerned the previous replacement sensor that I installed back in Sept last year was giving trouble already. I was concerned something was either poisoning the sensor, or the cause was PCM/wiring related.

I still hope they've diagnosed it correctly and it has nothing to do with the PCM. One would hope most of the 2.5 hours is diagnostic time! I will be querying the hours when I collect it this afternoon.

Also if I installed it myslef I doubt that they would offer the 2 year warranty?

 

[kerrin]

It all becomes clear reading the technicians repair details. The reason the sensor was intermittently failing was because the connection had been soldered which is apparently a no-no :whistling. It should have been crimped.

I have a spare sensor now and the fuel economy is back to its normal 8.6l/100km. :dance:

The labour included some other work so wasn't so not so bad after all.

 

[whitey66]

LOL oxygen travelling through the wire? :hit: :rofl:

Don't laugh too loud,because that is the truth.
The O2 sensor compares the amount of unburnt oxygen in the exhaust to the amount of oxygen outside the exhaust.This oxygen comes from the gaps between the strands in the wiring for the O2 sensor.
Do a bit of research then hit yourself on the head with a bigger hammer .

 

[kerrin]

Don't laugh too loud,because that is the truth.
The O2 sensor compares the amount of unburnt oxygen in the exhaust to the amount of oxygen outside the exhaust.This oxygen comes from the gaps between the strands in the wiring for the O2 sensor.
Do a bit of research then hit yourself on the head with a bigger hammer .

Looking at the sensor it has 4 wires (two power and two sensor) which are all identical standard plastic coated low voltage wires - with no stand gaps for air to pass..

The sensor does appear to have an outer cover on the back with a small gap. Would say this is where it gets its outside reading from if anywhere.

The third party sensor came without a plug attached, and with 4 wire crimps. I now know why the wire crimps where there. Solder seemed better at the time, but with hind sight I can see due to heat, moisture, and therefore oxidation the solder over time is now not the connection it use to be.

 

[kerrin]

this is really interesting reading...
OXYGEN SENSORS

"The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail."

I wonder if the 3rd party one breaths through the back, and the GM genuine ones breath through the wire. They do look slightly different...