what is the diffrences if it flashes or it stays on for the first time today my check engine light flashed like 2 min then it went off and came back on but it did something and now my truck seems faster i know the light stays on because i have no o2 sensors hooked up so it goes to safe fuel mode but y would it flash all the sudden?

Welcome to the site!

Assuming you have a GM truck, a flashing SES lamp typically indicates a problem with the emissions control system; this could be anything from an open gas cap to a misfire etc.

What's the year/make/model?

Flashing means its misfiring. Maybe due to the unhooked O2 sensor.

When a Check Engine, or Service Engine Soon light flashes, it is detecting a misfire condition (spark plug not firing as its supposed to). IF you don't have O2 sensors hooked up on a vehicle that is supposed to have them, then its probably switching excessively from Lean (too much air, not enough fuel), to Rich (too much fuel, not enough air), causing the engine to possibly seem more powerful, but also ruining a perfectly good set of spark plugs. If I were you, I'd at least install an O2 sensor simulator so that the computer has SOME form of reading, even if it is a fake one so that you can have a more "proper" fuel/air ratio.

Welcome to the site!

Assuming you have a GM truck, a flashing SES lamp typically indicates a problem with the emissions control system; this could be anything from an open gas cap to a misfire etc.

What's the year/make/model?

it is a 1996 chevy k1500 pickup z71 could it go off from bad brakes it doesnt do it everytime i start it. the boy i bought it from took off the o2 sensors because he could not find the wire harness on the intake where exactly does it go and what do i need to do to to get my oxygen sensors to work properly? how much and i looking at to spend?

Check Engine Lights are not in any way effected by brakes.

If you do the work yourself a couple of 0/2 sensors will not

be a big financial burden. You turn wrenches yourself?

Yeah i would definately recomend installing the Oxygen sensors. If you leave it in the condition it is, you are consuming alot of fuel as well as trashing your plugs and down the road you may trash your cat. converter.

Edited May 2, 200718 yr by Buickfosure

First thing, whatever nimrod you had reinstall the O2 sensors, was a clutz, you're not going to find the O2 sensor harness on the INTAKE, you will, however; find it on the EXHAUST. If they've been cut, you should be able to find the dangling wires somewhere...