O2 Sensors and Mileage

[AirForceAngler]

My '00 Z71 with the 5.3 has 106,000 miles on it now and the mileage seems to be going down. I used to average about 16 with 18+ on the highway, now I'm getting about 14 most of the time. It still has the original O2 sensors on it and I'm not getting any codes and it runs great! Will changing these out help with the mileage? I don't really want to spend that kind of money to replace items that are still working if it's not going to help.

 

Thanks!

 

[Bowler807]

If your truck is still running good, I think I would wait till spring to see if your mileage returns. Around here we are forced to use reformulated "winter" gas. I have 3 different vehicles and all have had a mileage decrease of around 3 mpg since the change in the gas. Your O2 sensor may be just fine. You may be experiencing the "winter gas" syndrome.

[AirForceAngler]

Good point, bowler, I forgot about the winter gas stuff. My HHR's mileage also fluctuates quite a bit based on what station I buy my gas at. Thanks.

[95Sierra2500]

Chances are it's just the 'winter grade' gasoline. However, when an O2 sensor starts to get shabby, then you can loose .5-1 mpg...usually not 3 mpg. If it doesn't come back in the spring, then I'd start looking for some other serious problem.

[redvett]

Its pretty much assured that with over 100000mi the O2 sensors are going south. They start to get lazy and will toggle less & that s what hurts mileage.

When a vehicle get that kind of mileage its time for so serious service.

[Rolandd]

I have to agree with redvett. The O2 sensor works by being coated with the same stuff that's in a cat converter. In the presense of hot exhaust if there is oxygen around it will heat up the same as a cat. The ECM measures the resistance across a wire to ground. The input power is usually 5 volts, the voltage drop should be between 2 and 4 volts. If there is 0 voltage drop or a short the system knows the unit has failed and will throw a code. However, if it is just not working effectively but the voltage is still in range to the ECM you can lose economy and power. Go to Napa or some other reputable parts supplier (not Kragan or Autozone or Petboys) and pick up a pair of sensors if you milage does not come back in the spring.

[fossil]

On 1996 and newer OBD-II systems you don't have to change out the O2 sensors for regular maintenance. The ECM constantly monitors the system and will detect a fault should they become faulty.

 

Here's a neat link explaining the system:

 

 

http://www.obdii.com/

[Rolandd]

On 1996 and newer OBD-II systems you don't have to change out the O2 sensors for regular maintenance. The ECM constantly monitors the system and will detect a fault should they become faulty.

 

Here's a neat link explaining the system:

 

 

http://www.obdii.com/

 

<{POST_SNAPBACK}>

 

 

 

I agree with this statement, but it does not change my opinion from above. The sensors' accuracy can slip without going out of range, which will impact economy and performance, as originally reported. I would not recommend changing any sensor indiscrimenantly, however if there are issues or it is recommended as a service procedure why wait for the sendor to fail completely? The cost for waiting may be damage to other components (e.g.: the cat coverter) or wasted fuel.

[Bish]

On 1996 and newer OBD-II systems you don't have to change out the O2 sensors for regular maintenance. The ECM constantly monitors the system and will detect a fault should they become faulty.

 

Here's a neat link explaining the system:

 

 

http://www.obdii.com/

 

<{POST_SNAPBACK}>

 

 

 

I agree with this statement, but it does not change my opinion from above. The sensors' accuracy can slip without going out of range, which will impact economy and performance, as originally reported. I would not recommend changing any sensor indiscrimenantly, however if there are issues or it is recommended as a service procedure why wait for the sendor to fail completely? The cost for waiting may be damage to other components (e.g.: the cat coverter) or wasted fuel.

 

<{POST_SNAPBACK}>

 

 

 

 

Agree. I replaced mine at 80K because my mileage had dropped steadily over the course of a year. I have a spreadsheet that tracks every tankful and it steadily dropped over a year to where is was 2mpg lower than my average. I replaced the o2 sensors and immediately got the 2 mpg back. I had no codes for bad sensors. I think they get lazy over time. Not completely failing but not performing as well as new. I can tell the exact date I changed them by looking at the mileage graph.

[C & A s Dad]

I have to agree with redvett.  The O2 sensor works by being coated with the same stuff that's in a cat converter.  In the presense of hot exhaust if there is oxygen around it will heat up the same as a cat.  The ECM measures the resistance across a wire to ground.  The input power is usually 5 volts, the voltage drop should be between 2 and 4 volts.  If there is 0 voltage drop or a short the system knows the unit has failed and will throw a code.  However, if it is just not working effectively but the voltage is still in range to the ECM you can lose economy and power.  Go to Napa or some other reputable parts supplier (not Kragan or Autozone or Petboys) and pick up a pair of sensors if you milage does not come back in the spring.

 

<{POST_SNAPBACK}>

 

 

 

I agree with the statement about the brand of sensor you buy. Bosch is our (CARQUEST) supplier and they are a huge OE supplier along with NGK. Both are great products but I tend to lean towards the Bosch simply because they test every sensor and they are OE in form, fit and function in every case. No adaptors or cutting of your wires. If you buy ours or any from Bosch you will notice they look used when you take them out of the box. This is the "burn in" testing process they go through.