Check engine light for HO2S

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Mar 21, 2003 | 02:56 PM

oldstylefseries

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Mountain Pass

Joined: Jan 2003

Posts: 136

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Check engine light for HO2S

Fellas,

New guy here. Basically a list lurker unless I recognize a problem that I've had and I can help. I am getting frustrated here. Been chasing a problem on my dad's truck. 96 f-150 (OBD II), 300 I6, and an E40d. Get a check engine light. Pull the codes ( I'm lucky enough to have access to a scanner) and find that the codes are for the HO2S monitors. Checked the obvious (fuses, broken wires, O2 sensor replacement.) Have 12 volts on the 2 white wires (O2 heater wires), but STILL get a check engine light. I'm out of ideas. Anybody else ever run into this?

Thanks,

Tim in Detroit

Mar 21, 2003 | 07:52 PM

Racerguy

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Joined: Aug 2002

Posts: 12,679

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From: BC, Canada

Check engine light for HO2S

You've tried new sensors?
The sensors just read what the engine is doing, rich or lean. You can have a problem upstream of the sensors and get a code for them. It's not neccesarily an O2 problem. If you have a misfire the sensors see extra oxygen in the exhaust and think it is lean so the PCM richens up the mixture. If you have a dirty MAF sensor or one that isn't reading correctly you can have O2 codes. Same with fuel pressure. Or a vacuum leak. Anything that can make the engine run rich or lean can cause an O2 code.
I think I'd start by checking for vacuum leaks, particularly the throttle body gasket and clean the MAF sensor.

Mar 21, 2003 | 08:17 PM

oldstylefseries

Thread Starter

Mountain Pass

Joined: Jan 2003

Posts: 136

Likes: 1

Check engine light for HO2S

Thanks for the reply, but I'm not referring to the OPERATION of the O2 sensors, but the HEATER circuit for the O2 sensors. The o2 sensors work fine. Just the heater circuit for the O2 sensors is throwing codes. There are NO codes for the O2 sensor function (rich/lean).

Thanks,

Tim

Mar 21, 2003 | 10:56 PM

Racerguy

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Joined: Aug 2002

Posts: 12,679

Likes: 15

From: BC, Canada

Check engine light for HO2S

oooooh ok

The O2 heaters are switched on their ground side through the PCM. The PCM is the only place they are connected.
If you can post the codes you got I can probably post the pinpoint tests out of the manual.

Mar 22, 2003 | 12:31 AM

steve83

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Joined: Nov 2002

Posts: 9,987

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From: Memphis, TN

Check engine light for HO2S

The heater side of the HEGO isn't connected to the computer, and therefore, doesn't throw codes. It's just wired hot thru the ignition switch to the Ppl/Or wire, which also powers several other key-on devices.

The codes you're getting are for the sensor part of the HEGO.