O2 Sensors

[Engine1s26]

2000 with a 5.4 only trouble codes are for all 4 O2 sensors. All for have been replaced but still getting the same codes. Scan tool shows the sensors are reading but the readings are erratic and jump all over and the mili amps are 0. Any ideas what might be the cause?

 

[Ulver]

I've got a feeling that the Skip and Stumble topic you made is related to this. Can you give us the specific code? Did you get all 4 codes at once? Also, did you get any kind of lean condition code?

 

[Killer Ride]

Do you have catalytic converters? How many miles on vehicles

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[Killer Ride]

If you do have Cats they could be clogged which will also give bad readings with the 02"s

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[Engine1s26]

PO420 and PO430 trouble codes. It says all 4 sensors are below threshold and it's always the same 4 at the same time. Even after I replaced all the sensors and reset the codes. The catalytic converters have been deleted so I was expecting trouble codes for the downstream sensors.

 

[Engine1s26]

269000 miles

 

[Engine1s26]

When I plugged it into the scan tool the sensors where all giving a read out but they were all bouncing around erratically, they may bounce from 30 up to 900 and back down to 600 and all over and would change when the throttle was pressed. However the milliamp reading on the sensor we're a flat 0. The mechanic with the scan tool said he figures it might be a wiring harness issue. But couldn't offer and solutions to fix it.

 

[Killer Ride]

That a pretty good diagnosis more than likely it is a wiring issue

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[Engine1s26]

I know you can buy the connector and even an extension set, because the factory connectors don't have a lot of slack and are hard to get to. Is there a way to troubleshoot the connector or even replace the harness if need be?I know when you buy the replacement connectors you just cut and splice them in. But I don't know how to fix the issue if it's not just the connector itself.

 

[stamp11127]

Lets see, you remove the cats, that throws codes that the cats aren't working properly because the downstream O2 sensor has the same reading as the upstream sensor for each bank.
The reading fluctuates because the pcm alternates between rich and lean which is picked up by the upstream sensor. The cat is supposed to smooth the reading but since it isnt there the downstream O2 sensor reading matches the upstream.
Since the scan tool is reading the sensors the harness is fine.

Any idea of the cause? Yea you removed the cats.

 

[Engine1s26]

The cats where deleted when I bought the vehicle, it run fine with occasional skip or sluggish response. All the technicians I have talked to says the cats being gone shouldn't affect the upstream side, and should only through a code for the downstream side. None of the up stream or downsteam reading were the same all four was wildly different. Even the Ford tech said I should only be getting codes for the back 2 and O2 sensor simulators should take care of that problem. I also have a F150 the same year and motor that has headers and straight pipes and all the 02 sensors read fine.

 

[stamp11127]

Visually check the harness where it goes by the exhaust system to make sure it hasn't burnt and shorted out.

Check here for how the fuel trims work. It explains how the O2 sensors and pcm work with the data they send to adjust the air/fuel mixture.
https://www.aa1car.com/library/what_is_fuel_trim.htm

 

[Engine1s26]

Ok thanks, will do

 

[thedonjuan211]

Cats are shot.