o2 sensor check engine light code.

[ashton]

My car is throwing the code for the o2 sensor. I have an 88 325i. My exhaust is unbolted from the resignator back. It also sputters during acceleration. Could the o2 sensor be the problem or something else? I just put a new fuel pump and fuel filter in because the fuel pump went out also. Lmk what you think. Thanks.

Ashton.

[billybobjoseph]

O2 sensor going out will cause the brain to run closed loop (limp mode) no matter how warm the engine gets. You would have the symptoms you describe.

[jlevie]

This code could actually be for a bad sensor, or it could be from an upset in the A/F ratio. Intake leaks, a fuel system problem, or ignition problem are common causes of upsets in the A/F ratio. Install a new O2 sensor if the one on the car has 100k on it, have a smoke test run, and run the fuel system tests.

[billybobjoseph]

you can test the o2 sensor with a digital volt meter and backprobes. The voltage from the signal wire ( make sure you have the right one ) and ground should vary between .1 or .2 volts and .8 or .9 volts. Main thing is that it crosses over the .45 volt mark. However, if the air fuel mixture is wrong your o2 sensor will stay either above or below that point and may be functioning correctly

[ashton]

you can test the o2 sensor with a digital volt meter and backprobes. The voltage from the signal wire ( make sure you have the right one ) and ground should vary between .1 or .2 volts and .8 or .9 volts. Main thing is that it crosses over the .45 volt mark. However, if the air fuel mixture is wrong your o2 sensor will stay either above or below that point and may be functioning correctly

Could the exhaust being unbolted be a factor?

[billybobjoseph]

If the exhaust is disconnected after the o2 sensor I don't think so, but I'm not 100% positive. While the motor is running there should be no air able to get back up the pipe but the decrease in pressure? Did you test your fuel pressure regulator?

[ashton]

If the exhaust is disconnected after the o2 sensor I don't think so, but I'm not 100% positive. While the motor is running there should be no air able to get back up the pipe but the decrease in pressure?

Its unbolted from the resignator back.

[billybobjoseph]

I noticed you replaced a lot of fuel system parts. Did you check your fuel pressure regulator?

[ashton]

I noticed you replaced a lot of fuel system parts. Did you check your fuel pressure regulator?

No I didn't. I guess I should do that.

[billybobjoseph]

Yeah if it goes you'll be running lean. Pull the vacuum hose ( small one goes to the intake manifold ) if there's fuel in it it's bad. If no fuel in the hose start the car then pull the #11 fuse and let it run till it dies. This will bring the fuel pressure down. Then take off the return hose and unbolt the regulator and pull it out. Clean it and blow into the opening where the return hose was connected. You should not be able to force air through it. When reinstalling it or installing a new one use a new o ring and put some lubricant on it. I use a little motor oil. Then slide it in straight and gently so as not to screw up the new o ring.

[ashton]

Yeah if it goes you'll be running lean. Pull the vacuum hose ( small one goes to the intake manifold ) if there's fuel in it it's bad. If no fuel in the hose start the car then pull the #11 fuse and let it run till it dies. This will bring the fuel pressure down. Then take off the return hose and unbolt the regulator and pull it out. Clean it and blow into the opening where the return hose was connected. You should not be able to force air through it. When reinstalling it or installing a new one use a new o ring and put some lubricant on it. I use a little motor oil. Then slide it in straight and gently so as not to screw up the new o ring.

But my car is throwing a o2 sensor check engine light code?

[billybobjoseph]

Yeah because your o2 sensor signal is not crossing the .45 volt mark. That doesn't necessarily mean your o2 sensor is bad. As Jlevie pointed out it may be that your car is running rich or lean. It would be a shame to buy a new o2 sensor and still have the same problem.

[ashton]

Yeah because your o2 sensor signal is not crossing the .45 volt mark. That doesn't necessarily mean your o2 sensor is bad. As Jlevie pointed out it may be that your car is running rich or lean. It would be a shame to buy a new o2 sensor and still have the same problem.

True.

[jlevie]

The O2 sensor is a scheduled maintenance item with a useful life of not more than 100k. While a meter check of the sensor will tell if it isn't dead, it won't tell you whether the sensor is still in spec. To check that you need a mixed gas flow bench. If the car's sensor qualifies on age, replace it. Then rule out intake leaks or a fuel system problem.

The O2 sensor is far enough forward in the down tubes that not having the catback part of the exhaust installed shouldn't cause a problem.

[billybobjoseph]

And check all the fuel system stuff, leaking injectors etc, then check for air leaks; intake boot, manifold gasket leaks. Good luck I hope you figure it out as inexpensively as possible. And I would defer to jlevie, you are supposed to replace it at 100K.