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Discussion Starter #1
I had CEL light and my indie mechanic replaced 2 O2 sensors on Bank 1 (upstream and downstream). Problem is they were both new downstream sensors. CEL now still lit. Did he create a problem? Or is this OK? Plan to buy 2 upstream sensors, install them, and move the other 2 both to downstream. Am I OK until I do that?
 

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I had CEL light and my indie mechanic replaced 2 O2 sensors on Bank 1 (upstream and downstream). Problem is they were both new downstream sensors. CEL now still lit. Did he create a problem? Or is this OK? Plan to buy 2 upstream sensors, install them, and move the other 2 both to downstream. Am I OK until I do that?
AFAIK, the only difference in upstream and downstream sensors is the length of the wiring.

I would have been comfortable with replacing all four of them at once.
 

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The sensors themselves are the same, only difference is the alignment pins in the connectors (which the aftermarket sensors don’t have at all) and possibly the length of the wires. Was the light still on when you picked up the car, or did it come on later? What was the code or codes it was throwing that made him want to replace the O2 sensors on that side? What code or codes is it throwing now?
 

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I'm with Mikey; the root problem usually isn't the sensor, unless they're 20+ years old and not switching.

Almost every time I've had that issue it was a vacuum leak; either vacuum tubing, or the intake manifold gasket.
 

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Get one of the cheap datalogging solutions that plugs into the odbII port, and works with your phone; then you can look at the o2 data and see what the deal is.

Throwing parts at the problem, based on our wild assed guesses is expensive, lol.
 

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Like Mike said earlier in the thread; why did you have the o2 sensors replaced? Was a code coming up for them, if so which code? It could be anything from a wiring problem, bad engine computer, or another sensor throwing it...
 

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Discussion Starter #9
Had codes read at Advance Auto. Don’t remember the codes, but they said it was the O2 heater circuit and said to replace sensors.
 

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Had codes read at Advance Auto. Don’t remember the codes, but they said it was the O2 heater circuit and said to replace sensors.
If the heater circuit goes bad on both up & downstream o2 sensors, of the same bank; good possibility that the engine computer is bad. In your original post you said both bank one sensors were replaced, that alone made suspect you have a bad heater circuit control in the engine computer. Now that your saying it was infact a heater control circuit code, sounds even more likely. If you dig through the forums here you can find several people have had the same thing happen to their cars, including myself.

You will need a code reader and have to do some diagnosing to get it fixed whatever it ends up being. If you replace the sensors with new ones and it throws the same heater circuit code after one or two ignition cycles it probably is the computer, or less likely a bad wiring harness.

I have said it in a few other posts; but I suspect these heater circuit failures are a more frequent problem then is known. I wonder if it's isolated to MN12s or other Fords of the same time frame have the same issue?
 

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Discussion Starter #12
If the heater circuit goes bad on both up & downstream o2 sensors, of the same bank; good possibility that the engine computer is bad. In your original post you said both bank one sensors were replaced, that alone made suspect you have a bad heater circuit control in the engine computer. Now that your saying it was infact a heater control circuit code, sounds even more likely. If you dig through the forums here you can find several people have had the same thing happen to their cars, including myself.

You will need a code reader and have to do some diagnosing to get it fixed whatever it ends up being. If you replace the sensors with new ones and it throws the same heater circuit code after one or two ignition cycles it probably is the computer, or less likely a bad wiring harness.

I have said it in a few other posts; but I suspect these heater circuit failures are a more frequent problem then is known. I wonder if it's isolated to MN12s or other Fords of the same time frame have the same issue?
If it is the computer, how tough is it to find one? These are 22 year old cars :frown2:
 

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Rebuilt computers are available. Most auto part stores should be able to order one without any problem.

I made the mistake of going used first, didn't know they rebuilt them still. Went through two used ones, the first one had both heater circuites bad, and the second had just one bank out. After getting a rebuilt I haven't had a problem since.
 

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Isn't it tough to get a rebuilt one with the same catch code? I've been told Advance and the like use a different numbering system.

Al
 

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To get the correct rebuilt computer you just need the year/engine/emission code (on door sticker, only 2 options for 96-97).
Lots of confusion about the catch codes. When I was digging through old threads here I found all sorts of conflicting information.

It seems like they don't make much of a difference if any. There was a thread a while back about it.
 

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Discussion Starter #16
If the heater circuit goes bad on both up & downstream o2 sensors, of the same bank; good possibility that the engine computer is bad. In your original post you said both bank one sensors were replaced, that alone made suspect you have a bad heater circuit control in the engine computer. Now that your saying it was infact a heater control circuit code, sounds even more likely. If you dig through the forums here you can find several people have had the same thing happen to their cars, including myself.

You will need a code reader and have to do some diagnosing to get it fixed whatever it ends up being. If you replace the sensors with new ones and it throws the same heater circuit code after one or two ignition cycles it probably is the computer, or less likely a bad wiring harness.

I have said it in a few other posts; but I suspect these heater circuit failures are a more frequent problem then is known. I wonder if it's isolated to MN12s or other Fords of the same time frame have the same issue?
Pulled the following codes today:
P1443, P0135, P0141, P0155, P0161.
The last 4 are codes for all 4 O2 sensors heating circuits, even though 2 were replaced last week. How can new sensors fail so soon?
The first code is supposedly evap purge valve, but I read that that code could be either causing or due to the other 4 (?)
What do I do?
 

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When I had a problem with this a few years ago, one downstream sensor had gone bad, and was pulling down the voltage on the whole O2 sensor circuit.

I now replace all 4 sensors at once when I have a problem, if they're over 10 years old.

There is a fuse for the heater circuit, I'd check it.

Several people have had problems with the EEC in 97 cars; I'm running an MBE2 code box in my 97 Tbird from a JY cougar, and have no more EEC problems.

The problem can also be a vacuum leak big enough to prevent closed loop operation; I had a bad manifold gasket, and it caused this code as well as others.

You really need a datalogging solution.



P1443 Evap code==Vacuum leak or bad egr solenoid

P0135 Oxygen O2 Sensor Heater Circuit Malfunction Front, bank 1

P0141 O2 Sensor Heater Circuit Malfunction Rear, Bank 1

P0155 O2 Sensor Heater Circuit Malfunction Front, Bank 2

P0161 O2 Sensor Heater Circuit Malfunction Bank2 rear


There is a "HEGO" fuse for the heaters, which might be blown. The rear O2s go through the transmission harness, which goes under the dash. The front O2s go through the engine harness, via the bulkhead connector on the passenger side.
https://forums.tccoa.com/6-general-tech/187954-multiple-02-sensor-codes-running-rich.html

https://forums.tccoa.com/7-engine-4-6l-5-4l/189411-97-thunderbird-lx-v8-p0155-p0161-new-o2-sensors-same-codes.html

https://forums.tccoa.com/7-engine-4-6l-5-4l/22445-ho2s-fault-codes-p0135-p0141-p0155-p0161.html

https://forums.tccoa.com/7-engine-4-6l-5-4l/131268-running-rich-o2s.html

https://forums.tccoa.com/6-general-tech/127963-p0135-p0155.html
 

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Good call on the HEGO fuse Grog, forgot about that.

What do I do?
From what you have said it could very well be...
-HEGO fuse
-Bad o2 Sensors
-Bad/Burnt Wiring harness ( behind the engine usually )
-Faulty Computer

Check the fuse, replace all the sensors, check the continuity of the harness and look for it being burned, replace the computer. That's pretty much what I did; but I also went through two bad used computers in the process. This was all after my original computer which was working perfectly randomly died on me. It was a very frustrating situation, I was about done with my Cougar until I finally figured it out.:bangwall:

When I had a problem with this a few years ago, one downstream sensor had gone bad, and was pulling down the voltage on the whole O2 sensor circuit.

I now replace all 4 sensors at once when I have a problem, if they're over 10 years old.
I believe each bank is on a separate circuit. Not doubting what you said or ran into... They both run power through one fuse, whatever circuit (or two circuits it seems) controls them in the engine computer, the banks are independent. I went through a computer with one side bad, and one with both sides bad, not to forget my original that just completely self destructed with no warning one day lol
 

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Discussion Starter #19
Good call on the HEGO fuse Grog, forgot about that.



From what you have said it could very well be...
-HEGO fuse
-Bad o2 Sensors
-Bad/Burnt Wiring harness ( behind the engine usually )
-Faulty Computer

Check the fuse, replace all the sensors, check the continuity of the harness and look for it being burned, replace the computer. That's pretty much what I did; but I also went through two bad used computers in the process. This was all after my original computer which was working perfectly randomly died on me. It was a very frustrating situation, I was about done with my Cougar until I finally figured it out.:bangwall:



I believe each bank is on a separate circuit. Not doubting what you said or ran into... They both run power through one fuse, whatever circuit (or two circuits it seems) controls them in the engine computer, the banks are independent. I went through a computer with one side bad, and one with both sides bad, not to forget my original that just completely self destructed with no warning one day lol

Did a search, but didn't find the location of the HEGO fuse. Where is it?
 

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Edit: Found the HEGO fuse (15A in the fuse block under the dash, it's labeled on the black cover but not in the manual) and it wasn't blown. Tested the terminal there for power and it's got 12V.
It's under the dash.
 
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