need help for my O2 sensor
 

as i mentioned in my previous post that my e36 328 engine light was on, and it turns out the O2 sensor not activated or someting... but my mechanician said might not be the O2 sensor problem because the O2 sensor will only activate when the engine is fully warm..

Also, another symptom is that when the car was on highway, the engine temperature when down to 45, on local was normal around 90 or 100

so, is this because of the bad thermostat? so i need replace thermostat first and see if this O2 sensor problem will fix?

any opinion would be appreciated!!

if you were closer to me I would scan it but I think your right thermostate look done.

1. Can you post the fault?

2. Replace the thermostat, based on the info you just provided. (Just for the over cooling issue)

3. Your car uses a Planar type O2 sensor (Siemens 41.x) which has a fast warm up time. It is looked at by the DME on start up but not monitored until the DME enters closed loop.

Mark.

thank you guys. just another quick question, if it is the o2 sensor needs to be replaced, do i need to replace all 4 of them? or just 2?

I had an engine light on when I bought the car - O2 sensor related. My mechanic said it wasn't totally shot, but partially working, 'could be on its way out or it could be dirty'. I started using 94 octane gas and in 1 month the light turned off.

really?:eek::eek: high octane gas cures that?

It could have been pure coincidence, but that was my experience.

anybody know if i should replace both or 4 of o2 sensors?
i checked the price online, the price is killing me!!! around 160 each!!!
maybe i have to look for some used ones......

Don't buy used ones. And you only need to replace the after cat ones if the diagnostics indicate they are dead. I think you should go to a mechanic if you aren't familiar with cars.