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Hey guys, I have a 96 Ford Ranger with about 250,000 miles that is having trouble passing smog. I have no check engine codes, but I cannot set the monitors. Specifically I cant set o2 heater sensor, o2 sensor and the cat monitor.
From reading other forums, it seems to all go back to the o2 heater. The cat wont set without o2, and o2 wont set without o2 heater.
From looking at the live data on the obd2 scanner, I found that the upstream o2 sensor is working normally, but the downstream sensor is stuck at 0V. I figured that the sensor doesn't produce voltage because it doesn't get hot enough because the heater is bad. I check the heater coil, but it seems okay.
Next I checked the wiring and as far as I could tell, the wiring is good, but I may have an issue with the pcm. If I back probe pin 93(upstream heater) and pin 95 (downstream heater), both pins "see" 12 volts with the key on engine off, however only pin 93 grounds itself when the engine starts, so only the upstream sensor is getting heated. Pin 95 remains at battery voltage.
I tried with a different pcm and got the same result. So there might be a wiring issue with the downstream sensor that is preventing pin 95(downstream heater) from grounding. I swapped pin 93 and pin 95, so that if there is a wiring issue, pin 93 would now refuse to ground itself. However with the pins swapped, its still pin 95 that refusing to ground.
Seems unlikely that I would have the same exact problem on both PCMs. Is this normal behavior for the downstream o2 heater to not kick in?
I've tried the drive cycle multiple times with no changes. I'm kind of out of ideas on how to proceed.
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