O/D and check engine light is on. Drives fine. Why is it on?

fuel filter or fuel pump chevy didn't add fuel pressure sensing to its ck engine computer till 2011

and sorry to tell ya but blazers have a common prob with fuel pumps going bad , just ask a parts guy on how many he sells a year , you;ll get the sad story

Many times check engine lights are disabled to prevent them coming on. Turn the ignition on without starting the engine, the light should be on. Most auto parts stores will do an OBS2 check free to diagnose problems.

A vehicle check engine light can come on for a variety of reasons. Many times your vehicle will run perfectly fine even with a sensor that is bad. You still want to get these fixed due to the fact that it can cause lower gas mileage or in time cause problems with your vehicle. If you go to Auto zone they can plug a computer into your car for free and tell you what is bad. Once those problems are fixed the same place can check your vehicle again and clear the check engine light.

Yes, a knock sensor can cause the check engine light to come on. I would change out the sensor and see if you come up with any other codes.

Your check engine light is an emissions warning. Your vehicle will not pass smog with the engine light on. You can go to kragen or other auto parts stores and buy a GM code reader for it. Though it runs fine, its telling you that a sensor or something is bad.

Has the check engine light came on. Sound like a O2 sensor. But you can have the codes read for FREE at any Advance or Auto Zone Store. Hope this helps.

Find out why the check engine light is on, and fix it.

you have to get scanned for fault codes..possible camshaft sensor if you have starting issues..if car is working fine,could be an evap leak..let me know

if you live in the states autozone will scan the codes for free

you need to find out what codes have been set
one of your coil packs is going bad.
the code should tell you which one
let us know how you do
later
paul