O2 Sensor Heater Problem
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Junior User
Joined: Jun 2002
Posts: 61
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O2 Sensor Heater Problem
I have a 1996 F150 with a 4.9 I6. It keeps throwing codes for the O2 sensor heaters. I have changed all 3 of the sensors out and reset the CEL but it keeps coming back. Does anyone have any ideas what may be causing this?
The codes that I am getting are: P0135, P0141, and P0155.
HL
The codes that I am getting are: P0135, P0141, and P0155.
HL
Thread Starter
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Junior User
Joined: Jun 2002
Posts: 61
Likes: 1
O2 Sensor Heater Problem
I did check the wiring at the O2 sensor plug with a meter and there is 12 volts. It seems that the heater should work (and I think it does work because the truck runs fine). It was running quite rich and stalling out on me before I changed the O2 sensors but now it runs good. I just can't figure out why I keep getting the codes.
I have reset the codes close to 10 times but they keep coming back. I am beginning to think that the problem is rooted much deeper, possibly in the ECU itself. Is there a way of checking to see if the O2 sensor heater actually is working or not?
I have reset the codes close to 10 times but they keep coming back. I am beginning to think that the problem is rooted much deeper, possibly in the ECU itself. Is there a way of checking to see if the O2 sensor heater actually is working or not?
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
O2 Sensor Heater Problem
Yeah, put 12V to it and don't touch. 
Have you tested ACROSS the 2 wires for the heater AT the EEC connector? That's where the computer is checking - see what it's seeing.
Have you tested ACROSS the 2 wires for the heater AT the EEC connector? That's where the computer is checking - see what it's seeing.
Thread Starter
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Junior User
Joined: Jun 2002
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O2 Sensor Heater Problem
I just checked the power supply at the O2 sensor plug and I don't have 12 volts. Don't know what I did wrong last time but I definitely do not have power to the heater in the sensor. I would like to check the other end of the wiring harness. Can someone tell me where the power for the O2 sensor originates?
My guess is the EEC but I don't even know where the EEC is located in this truck. My Haynes manual completely ignores the location or removal of the EEC.
HL
My guess is the EEC but I don't even know where the EEC is located in this truck. My Haynes manual completely ignores the location or removal of the EEC.
HL
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
O2 Sensor Heater Problem
The EEC is between the e-brake pedal and the fender, but it's accessed thru the engine compartment. Just look below & outboard of your brake booster. All 3 HEGOs are powered straight off the EEC power relay thru the Red wire that runs to ALL the sensors & injectors.
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Junior User
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O2 Sensor Heater Problem
Thanks Steve83.
That should be exactly what I am looking for. I'll have a look as soon as the wife gets home from work (you know, wife's truck, no maintenance until it's almost dead...).
Is the power relay that you speak of specifically for the HEGO's or does it power other things as well? I am thinking this could likely be a bad relay.
That should be exactly what I am looking for. I'll have a look as soon as the wife gets home from work (you know, wife's truck, no maintenance until it's almost dead...).
Is the power relay that you speak of specifically for the HEGO's or does it power other things as well? I am thinking this could likely be a bad relay.
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Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
O2 Sensor Heater Problem
They come off the EEC power relay, like every other sensor. If it was the relay, the computer wouldn't come on; the injectors wouldn't open; etc. It must be a bad connector, bad wire, or bad HEGO.
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