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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 33048
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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1996 Ford Thunderbird: he 4.6l V8..OBDII..O2 sensors

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My son has a 1996 Ford Thunderbird witht he 4.6l V8. The OBDII reader shows all four O2 sensors. Not likely the case. My sons put new O2 sensors in and still the check engine light comes on. Turns out that he isn't getting any power to all four O2 sensors. All the fuses (especially #s 15 and 3) check out fine. Is there a main fuse for the O2 sensors located somewhere else? Could this be a relay or (heaven forbid) the main computer? My son is trying to fix this on a limited budget so please help. Thanks.

HiCustomer Thank you for asking your question on Just Answer.

Can you tell me the code your getting?

Customer: replied 8 years ago.
Reply to Ron's Post: You mean the OBDII code? If so my other son did this at the auto parts store weeks ago. I would need to check with him but he told me the code read that the O2 sensors are bad. I've got to run home and will probably need to contact you later.
Ok if you can get me the code or codes I help you figure this out. Just return to this question as its not likely the HO2Ss are bad.Im Dont hit accept till we figure this out.
Ron and other Ford Specialists are ready to help you
Customer: replied 8 years ago.
I heard back from the mechanic and he said the OBDII codes are PO135, PO141, PO155 and PO161 which apparently are heater short faults.


Thank you for asking your question on Just Answer. In most case when you have this combonation of code you likely looking at a bad PCM (computer)

Check resistance of the heater circuits from Powertrain Control Module (PCM) connector pin 71 or 97 to pin 93, 94, 95, 96 and resistance should be 3-30 ohms. Then turn the key on, all for heater control pins (93, 94, 95, 96) should have battery voltage. If so, using an ammeter, ground each pin one at a time to energize the heaters and check their amp draw. The amp draw per heater should be 4A or less and should start to drop as the heater heats up. If all heater circuit checks are OK, replace the PCM

The PCM is located behind the passenger side kick panel inside the car.

Customer: replied 8 years ago.
I should find out more today. Don't worry, I won't forget about you. I just don't have the car right now and the mechanic will be checking on your suggestions.
No problem, just let me know .
Customer: replied 8 years ago.
The mechanic who has the car wants to make sure that the power loss to the O2 sensors isn't a relay or something else. He was trying to track down where the relay is. Also, he thought there might be a master fuse or something.
Customer: replied 8 years ago.
Is there a master fuse or a relay that might be the source of the power loss?
Yes the power comes from the PCM relay(powertrain control) relay in the LH fuse panel in the Engine compartment.
Customer: replied 8 years ago.
Is that something that can be replaced?
If it was bad the engine would not even run. Have him run the test I sent.