Saturn Ion 2004..19041 miles..My check engine light came on and I stopped at Advanced and had one of the guys read the codes.He said it was code P0140..he went on to say the code reader said no voltage going to (or through) the O2 sensor.He said to check to see if the wire had fallen off the sensor.Getting ready to check that but knowing what those plugs look like I doubt it simply fell off.Any ideas ? This car used to belong to my mother and was never driven above 40 until last year when I got it and I drove it to Florida which I was planning to do in about 5 days until this light popped on.Could it be any thing to do with the 19000 miles being a time to get something checked?Thanks in advance.

 

Well, I would touch base with your local dealership, and see if they have any information as to previous service(s) performed on that vehicle. Once I had that in my hands, it would point to any service(s) that was needed immediately.

Loss of power to the downstream O2 sensor might cause the vehicle to have low MPG, and you will not be able to pass a SMOG test if you need to renew your certificate.

 

No previous service other than oil changes.
Is there any test I can do on the o2 sensor? I checked the fuse for the sensors and its good.Can I test the wires going TO the sensor?
Edited by: 12v testlight

 

You have to find the reason for the loss of signal from the O2 sensor. It could be a bad connector or an open sensor.

Voltage is being output to the sensor, otherwise there would be a P137 or P138 (voltage low/high). P139 would indicate a signal being returned, but no change detected from the sensor.

P140 says no signal is being returned from the sensor (open circuit).

 

Thank you very much for the response. This car looks like NEW underneath,as it should being garage kept and only 19k.Initially I was working from the top and was looking at the 02 sensor on the engine side of the converter.I pulled the connector apart and it looked perfectly clean.I went to Autozone looking for a socket to remove the sensor.The young man said let me check your codes and he did and he got the same P140 code that Advanced got and he snickered a little when he saw I was looking at the wrong sensor.So he got me on the right track and I got under the car and located the correct sensor.I viewed the wiring path and saw no problems between the sensor and the connector.I pulled the connector apart and it was hospital clean inside.I removed the wire from its holder and removed the sensor from the exhaust.Wasn''''t covered in soot,looked clean.Put it back together and drove the car (car runs perfect)for at least 20 min. but the light remained on.

I didnt know the codes on these newer cars were so specific.The codes I was used to on older GM cars were pretty generic.

Sounds as if, if the wire didnt fall off and didnt get cut or burned in 2 by the exhaust it HAS to be an open sensor.Being that the connector inside is so clean am I wasting my time trying to bend the contacts to make better connection ? I don''''t mind buying a new sensor but am hoping to be able to pinpoint the problem rather than just throwing in new parts. I notice the sensor has 4 wiresis there a sensor circuit and a heated circuit?Does the p140 code tell which circuit is open ? Can I use an ohm meter to test the sensor looking for an open? If I do replace the sensor should I use the Bosch brand or the generic fit all type? Looks like $45 verses $140.
Thanks for reading my long post and Happy New Year.

edit-One last question-Should or can I do a comparison test with my ohm meter using the forward 02 sensor to compare readings ?



Edited by: 12v testlight

 

I really do not know if you can compare cold readings with the upstream unit or not (never tried it). I have tried, however, to use an after-market (generic) part - it did not work for me, but I would defer comment to others here on the Forum with more experience in this area. Low Saturn or SW2cam or Derf just to name a few ...

 

Thanks...I did a search and saw where some have said the one I''m working on wont make the car run bad.What does this sensor do ?The reason I ask is if this happened when I was on the road half way to Florida should I be finding a room or just driving on and getting it looked at when I get there? The book seems to say if the light is on all the time its not real serious but if the light is flashing it is serious.

 

That sensor is the final check of the exhaust. Basically monitoring the health/well-being of the catalytic system.

You are right in the assumption that a steady-state lamp indicates a fault, and a flashing light indicates a failure of a more serious nature.

I would continue my trip, and have it serviced when I arrived at my destination (but that is my opinion - feel free to do as you see fit).

 

Thanks again for taking the time to discuss this with me. I have a small update. Last night after checking the items I mentioned earlier I also checked each fuse with a test light and moved each one and pushed in on each relay in both fuse boxes.After driving the car the light remained on. Then I did the oldschool thing and disconnected the battery and went in the house. I was told that on the new systems you dont need to disconnect the battery to clear codes they will clear as you drive. I came out this morning connected the battery and started the car and the light came on as usual and went out. I drove the car over 15 miles varying the load from light to full throttle and during that time made 3 stops to go in a store.When coming out the light came on and went off as it should.
If all I did was clear the computer memory how long (if in fact the sensor is an open circuit) will it be before the computer recognizes the "open" and turns the check engine light back on?
If the open has actually disappeared should I assume the open was a result of a connector and not the sensor because I couldnt have done anything to have repaired the open inside the sensor by simply moving wires? (the sensor doesnt receive any grounding from its thread connection in the exhaust does it? )
Thanks

 

If it was simply a loose connection, you should be good to go.

If the sensor is truly inoperative, it may take a little while before the PCM detects the inactivity, and sets the code again. I do not know what the time delay is necessary for that to occur ...