Why is my 02 sensor not pulsing and not throwing a code?

  • 3.9L
  • 6 CYL
  • 2WD
  • 196,000 MILES
I have tracked down all vacuum and exhaust leaks, I've replaced the spark plugs, wires, and coil pack, I replaced one 02 sensor, and put the original working one on the side that's not pulsing, the TPS, MAF, and IAC all work properly, the EGR has been replaced, and I don't know what else would cause a good 02 sensor to be lazy.
Do you
have the same problem?
Tuesday, May 16th, 2023 AT 7:24 AM

1 Reply

Hello, if the heater circuit for the sensor is not working, that can cause it to be slow/lazy, what voltage reading are you getting from it? I assume this is a sensor 1(front 02). Which Bank is it? Let me guess, bank 1 sensor 1?
Are you getting any other codes at all? It looks like Bank 1 Sensor 1 is the only one out of the 4 that gets it heater circuit power feed from a different Splice location, you can see in the 1st diagram, the Splice S164 is near the number 1 Fuel Injector, but verify that there is 12volts coming to the B1 S1 heater circuit. Now most of these are PWM (Pulse width modulated on the Ground side, ) so the ECM will pulse the ground side of the heater circuit to control it. I have seen some of them intentionally shut down the heater circuit if there is a circuit fault. For example, I had a vehicle with a open circuit inside the oxygen sensor heater and after I would erase the code the ECM would start to pulse the ground side again until it detected the fault, and 10.6 seconds after it would shut down the heater circuit to protect the ECM driver from too much current flow. But since you are not seeing any codes (and Fords sometimes take forever to set codes, sometimes they won't at all). But verify that there is power on that 02 sensors wires, it looks like they are Red/Yellow and Red/White. Usually at the 02 connector the heater circuit is the 2 wires that are the same color.
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Tuesday, May 16th, 2023 AT 12:00 PM

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