All 4 O2 sensors failing


Old 12-05-06, 08:12 AM
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All 4 O2 sensors failing

I have a 97 Thunderbird 6Cyl Automatic with 70K that has been running just fine. Now with emissions testing around the corner it is acting up. The check engine light is on with DTCs of P0135, P0141, P0155, P0161. My mechanic checked the car and reported that he doubts the O2s are all bad. Unfortunately, he says he just does not know. Actually I appreciate his honesty but that still leaves me with the problem.
I had a transmission pan gasket leak just prior to this and I can't help but to wonder if the trany fluid might have caused some sort of electrical resistance, enough to cause improper control voltage (ie. circuit fault) but still allowing control voltage.

The engine has not been worked on in the last 5 years which would seem to rule out improper gasket sealant. I saw a post that mentioned plastic intake gaskets going bad but I have no idea how to follow up on that one.

I would like to just run new wires temporarily to all sensors but this is probably much more difficult than it sounds.

I am looking for a feasible way of testing this situation against an unlikely trouble code scenario. I have a multimeter but just saying test the control voltage leaves me wondering just where to put the leads.

Any ideas, suggestions, or just plain guesss would be greatly appreciated. TIA
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Old 12-05-06, 08:49 AM
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Definetly test them before doing anything. Here's a link to a generic test procedure.

I don't see all 4 going out at once. Definetly sounds like a electrical issue. These sensors I believe go directly to the PCM (powertrain control module). Hopefully thats not the issue.
Old 12-05-06, 03:11 PM
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Not sure what the Ford codes are telling him, but I also doubt that all or any of the O2 sensors are bad. It is likely one component related to something the codes say. Can you tell us what the codes translate?? Unfortunately modern engines are run by computers. When one component fails it can affect several other components. Too rich a mixture can tell the O2 sensors that something is wrong, lean out the mixture, then something says, not enough gas- need more, etc., etc.
Old 12-06-06, 08:41 AM
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P0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
P0141: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0155: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
P0161: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

These codes mention heater circuit malfunction, not the sensor voltage itself. All I can think of is to look for anything that is common to all these O2 sensors, like one pair of wires branching off to all heaters for each sensor. It would be helpful to have an electrical wiring diagram for the engine.
Old 12-06-06, 11:39 AM
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A local library should have the repair manual for this vehicle. Try that.
Old 12-06-06, 02:55 PM
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Keep in mind that those computer codes point to a problem area, never to a specific component. They are not that sophisticated yet. What you posted suggests a failure, but not the O2 sensors themselves.
Old 12-06-06, 03:28 PM
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If they were lean/rich codes I'd be more apt to be looking for a central problem.........O2 heater circuits, however almost ALWAYS lead to an O2 replacemant........How long has the CEL been on????? Is it possible they have been dropping out one at a time?????
Old 12-06-06, 07:44 PM
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I'd start by checking the fuse for the O2 heaters.

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