O2 sensor issues with my 97 Ranger 4.0 - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 05-23-2016
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O2 sensor issues with my 97 Ranger 4.0

I'm working on a 97 4.0 that was abandoned for 4 years. Did tune-up stuff: plugs, wires, filters, fluid flush...also replaced coolant temp sensor, thermostat, sending unit to fix a nonfunctional temp guage. Replaced EGR, hoses, and dpfe unit because they looked very clogged and dirty. I also replaced the bank 2 oxygen sensor, but have not yet replaced the two bank 1 sensors. I'm not sure if that's going to fix my problem. I'm still getting the following 5 obd2 codes:

P1152(Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Rich - Bank No. 2)
P1132(Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Rich - Bank No. 1)
P0135(Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P0155(Oxygen Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
P0141(O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 2)

Please help!!!
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Old 05-23-2016
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Should be a fuse in engine fuse box that powers all 3 of the heaters in the O2 sensors, the computer monitors that heater voltage and no voltage is what sets those codes.
If there was only one O2 sensor with that code then I would suspect wiring or the heater in the sensor was bad.
But all 3 is most likely a blown fuse

That may also solve the Rich codes

The Bank 1 sensor 2's usually lasts the life of the vehicle, it should only "see" clean exhaust being located after the Cat Converter.

The Bank 1 and Bank 2 sensor 1's get the straight exhaust from the engine and are usually OK for 150k miles, spec is 100k.
MPG tends to go down as these O2s wear out, but it doesn't cause major issues, just costs you more money in fuel.

Clean the MAF sensor, always.


Rich code means the computer has cut down fuel injector open time to a pre-set limit(which sets that code) and O2 sensors are still showing less Oxygen content(rich) in exhaust than it should.

Because engine sat for awhile you could have a few fuel injectors that are sticking, letting in too much fuel.
A few because if it was just one then only 1 bank would show Rich code
Run some Seafoam, or similar, injector cleaner in the gas tank that should help clean them up.

On the fuel rail there is a fuel pressure regulator(FPR), passenger side top front of engine, the Return Fuel hose is connected to it, and also a vacuum hose.
Pull off that vacuum hose and check it for fuel, or start engine with it off and see if fuel comes out of FPR, it shouldn't of course.
It it sat dry the rubber in the FPR diaphragm may have cracked and is leaking, and the vacuum line sucks that extra fuel into the intake causing both banks to run rich

Is the exhaust showing black smoke after it is warmed up?

Last edited by RonD; 05-23-2016 at 10:22 PM.
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Old 05-23-2016
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No. a little white smoke when idling, but goes away when I give it gas. I checked the O2 fuse and it was good. replaced it anyways. cleaned the MAF. also ran some Lucas fuel injector cleaner through it...two tanks worth.
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Old 05-23-2016
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Did the Fuse have power when key is on?

Power comes from PCM 30amp fuse but engine wouldn't start if that was out.

the 3 O2's heater power comes from same Red wire at PCM relay, the Light Blue/orange stripe wire at each O2 is the 12volts from the heater fuse(#3, 15amp).

Then each O2 heater has a separate Ground wire that runs to the PCM, the PCM grounds those 3 wires and that's how it monitors if they are getting power.
Long shot would be that a ground wire for the computer is bad and they would all use the same ground so voltage can't flow so you get the codes.

Computer has several Ground point wires and none are shared inside the computer.
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