Hello,

I've been chasing O2 sensor codes for about the last three months. To begin, let me walk you through what I have done thus far. I am receiving the following CEL codes for a 1996 F-150 XLT (V8 - 5.0) 4X4,

P0135 - O2 Sensor Heater Bank 1/Sensor 1

P0141 - O2 Sensor Heater Circuit Bank 1/Sensor 2

P0155 - O2 Sesnor Heater Circuit Bank 2/Sensor 1

P0133 - O2 Sensor Heater Circuit Slow Response Bank 1/Sensor 1

I have replaced all three O2 sensors 1.5 months ago, cleared codes, ran the truck and still receiving the codes.

My initial thought was a had a grounding issue. I cleaned all grounding points and reattached, still receiving codes.

I attached a clip to the metal frame of the O2 sensor and attached other end to the negative battery post. In the hopes to provide a direct ground to the O2 sensor...NO JOY!

My next step is to replace the PCU. Is this a necessary step or is there something I can do prior to replacing the PCU?

Is there a way to tell what PCU you have in the truck without taking out the PCU...in other words, via VIN?

Thanks.

 

You need to verify that you're actually getting heater power to the O2 sensors first.

 

I dont have diagrams for a 96, but there should be a fuse for the 02 heater circuits.

 

Replaced the fuze....nothing!

I'm at the point of either flashing or replacing the PCU?

Any thoughts/suggestions?

 

Do I need to pull the O2 sensor and bench test each one?

What am I looking for with regards to the heater power?

 

Heres how it works on my 97 5.0. The PCM power relay closes with KOEO (key on engine off)& sends 12 volts to the 02 heaters on the Light blue/orange stripe wire. The PCM grounds that voltage to turn the heaters on.

Dont know if your color coding is the same, but one of the wires to each 02 sensor should have 12 volts from the PCM relay.

 

87XLT thanks for the info!

Just to clarify, I need to put a volt meter on the o2 sensor heater wires to monitor the voltage. On the Bosch O2 sensor wiring diagram I have four wires (black=signal, gray=ground, 2 x white = heater)? Does the test need to occur on the O2 sensor wire while connected or directly testing the wiring harness? And the volt readout should be 12 volts on each wire or 6 a piece?

Thanks again!

 

Trying to figure this out from online diagrams is a challenge, but from what i see the wire from fuse to heater circuit should be purple/orange stripe & from heater to ground G101 is solid black. With the key on these wires should read 12 volts. I'm not seeing the grey or white you mentioned.

If i had a 96 F150 I would have the factory diagrams and figuring this out would be much easier.

 

It'd probably be best to test with the O2 sensor plugged in. You should have 12 volts across the heater wires. The truck applies 12 volts to one wire, and then grounds the other through the PCM. It's just a simple resistive heater, so it doesn't care about polarity.

 

If your Ford dealer will photocopy the "5.0 engine controls diagrams" from the 96 F150 EVTM you will know in a couple of seconds exactly how the 02 circuit is wired & how it works so you can test it.

This is what i used to do b4 i started buying the manuals.

Bottom line is you should see 12 volts from the fuse KOEO.