anyone know what color the signal and heater wires are on a '97 4.6l f-150 pre-cat drivers side o2 sensor?

 

The heater wires are red/yellow and yellow/lightblue. The red/yellow is the hot wire, the yellow/lightblue goes to the computer.

The signal wires are grey/red and red/black. The grey/red is the hot wire and the red/black goes to the computer.

 

thank you, I'm going to check for voltages before I replace the sensor.

 

I checked the color codes & mine are all different. My heater wire is a solid red color & is a size heavier than the other three. According to the Haynes manual the grd for it should be alongside it to the left, its color is yellow. I don't get 12v between them but between the wire below it which is a brown wire& should be the signal ground according to the location shown in the Haynes manual. I found a break in the heater wire on the o2 wire harness when checking continuity between the pin and wire & got it connected but it still shows a heater trouble code-if the Haynes manual is right, the ground for the heater is probably open on the supply side of the connector but I can't get in there to check for continuity between the pin & attached wire. Do you know which terminal at the PCM links with the heater grd pin & where its located at the connector or if the connector can be disassembled? Thanks for any help as I'm out of ideas.

 

Here is the needed schematic: 1997 F150 4.6 Engine Controls.pdf

The sensor at issue is HO2S#21 and is on page 24-4.

All color code references are for the harness BEFORE the connector as the actual sensor harness can vary depending on manufacturer.

The heater circuit is: RED wire is HOT IN START/RUN, the YELLOW/LIGHT BLUE is the line to the PCM that is "grounded" by the computer to turn on the heater.

The signal circuit is: GRAY/RED is SIGNAL RTN (ground) and the RED/BLACK wire is the signal output back to the PCM.

The heater in the sensor can be tested with an ohmmeter. Book calls for a resistance value between 3 and 30 ohms.

Steve

 

wow,great link thank you. Looks like terminal 94 at the pcm is the one I want to check. Do you know if they are labelled? I'd hate to risk taking everything apart and not being able to identify it. I found an 'EVTM' manual & ordered it online so I should be good for future problems. Thanks again!

 

These are from the EVTM. They get printed as a pdf and then uploaded as needed to the free file sharing site.

Here's the PCM connector. You'll need all three pages. Disregard the latter part of page 3.

1997 F150 C174 Pg 1.pdf
1997 F150 C174 pg 2.pdf
1997 F150 C174 pg 3.pdf

Steve

 

Check the O2 voltage while running the tip through a propane torch flame.
A bonus to doing that is it will clean the sensor at the same time, If you got
buildup on it it will read slow and not react as quickly to A/f changes. Try 20
seconds in flame wipe it off, if still not clean try another 10 until the build up
is pretty much gone. Of course you will not get it shining new you just need it
to be cleaner than it is now.

 

Since you didn't read the thread before commenting... he has a heater circuit fault. Checking the voltage as described with a propane torch is irrelevent.

 

If the heater in the O2 is not working properly the sensor is probably dirty and needs to be cleaned before doing much of anything else. Since he had a break in the heater wire it is basically not self heating and getting all crudded up!! I am sure you will just tell him to replace the sensors wholesale instead of cleaning the ones he has, just like
everyone does, throw a new o2 sensor at the problem that'll fix it.

 

I think he is actually trying to repair his system....

 

Thanks for all the advice, I would clean the tip if I could get at it but I can't budge it-no room unless I remove more parts, the socket is up against the floor pan. I'm going to try to repair the harness connector if I can get to it, it's way up behind the motor,thanks for the schematic. Right now I'm working on my bronco II and driving my buick to work..thank God for beaters!