# Oxygen sensor **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** fuel-economy\ **Created:** [September 27, 2007, 3:25pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179 "2007-09-27T15:25:25Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![oldsmobile](https://avatars.discourse-cdn.com/v4/letter/o/c2a13f/32.png) [@oldsmobile](https://community.cartalk.com/u/oldsmobile)\ **Post date:** [September 27, 2007, 3:25pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/1 "2007-09-27T15:25:25Z")
i have a 98 olds intrigue 3.8L V6 automatic. 150,000 miles. if i change the oxygen sensor, will that improve my gas mileage? also, how do i know if the catalitic converter needs replacing? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [September 27, 2007, 3:40pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/2 "2007-09-27T15:40:53Z")
If there’s no Check Engine light on, there’s nothing wrong with the O2 sensors. The OBDII engine management system monitors the sensors very closely. If there were a problem the catalytic converter, the O2 sensor after the cat would detect this, and the Check Engine light would come on. So, if there’s no Check Engine light, everything is working properly. Tester ---
**Author:** ![markmast](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@markmast](https://community.cartalk.com/u/markmast)\ **Post date:** [September 27, 2007, 3:41pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/3 "2007-09-27T15:41:20Z")
the short answer is that if the existing oxygen sensors are OK, changing them will not improve mileage. You have three oxygen sensors on your car. They are located in each exhaust manifold and one downstream of the catalytic converter. The sensors in the manifold control the fuel mixture and will cause poor fuel economy when they fail. The sensor downstream of the catalytic converter checks the performance of the converter, but does not effect fuel economy. If any of these items fail (sensors or converter) you would get a check engine light on your dashboard to alert you of the problem ---
**Author:** ![oldsmobile](https://avatars.discourse-cdn.com/v4/letter/o/c2a13f/32.png) [@oldsmobile](https://community.cartalk.com/u/oldsmobile)\ **Post date:** [September 27, 2007, 3:47pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/4 "2007-09-27T15:47:29Z")
excellant! thanks for clearing that up. on the same car my cruise control stopped working. the switch comes on when pressed, but will not engage. whats up? ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [September 27, 2007, 3:56pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/5 "2007-09-27T15:56:50Z")
“my cruise control stopped working. the switch comes on when pressed, but will not engage. whats up?” It could be many things, but I would first check to make sure the brake lights are working when you apply them. A defective brake light switch is not an unusual problem and they are usually cheap and easy to replace. ---
**Author:** ![Jad2007](https://avatars.discourse-cdn.com/v4/letter/j/dec6dc/32.png) [@Jad2007](https://community.cartalk.com/u/Jad2007)\ **Post date:** [September 27, 2007, 4:00pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/6 "2007-09-27T16:00:43Z")
What about an 85 Olds Cutlass? No OBDII on there right? How do you test to see if the O2 sensors need replacing on an older car like this? Also, how do you retrieve codes on a pre-OBD system or know that there are codes that have been saved from a problem? Or do they not store codes? Thanks, Jad ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [September 27, 2007, 5:38pm UTC](https://community.cartalk.com/t/oxygen-sensor/5179/7 "2007-09-27T17:38:44Z")
Has your fuel mileage decreased? If the engine coolant temperature sensor doesn’t tell the engine computer that the engine is warm enough, the engine computer won’t listen to the oxygen sensors. The result is, the engine runs rich and fuel mileage suffers. Using your handy dandy Haynes, or Chilton’s manual, and a digital multimeter, you can do the ohms check (at different temperatures) on the engine coolant temperature sensor (ect). If in doubt of ect’s accuracy, you change it.