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Overheating and Can't pass smog 96 Protege

My 96 Mazda Protege failed to pass CA Smog test because the PCM Monitors hadn’t ‘reset’. I’ve driven it 3K miles, and they just won’t reset. I took it to the dealer and he said it was over-heating and needs a new coolant temp sensor. I’ve replaced both of them, and the radiator fan isn’t activated by heat (it will come on if I turn on the AC).

At this point I’m guessing that the PCM (Powertrain Control Monitor - i.e., computer) is malfunctioning. But I’ve pulled it, and it looks fine (visual inspection). Does anybody have any words of wisdom?

Go to an auto parts store and have them plug in a scan tool, check for new codes, and clear the codes. (Many stores will do this for free.) If the check engine light comes back on, then you didn’t fix the problem.

I left out that the PCM isn’t displaying any malfunction codes. The MIL doesn’t light up, and when I hook up an OBDII monitor, there are no codes. The OBDII monitor does show that the Catalyst, Evaporative System, Oxygen Sensor, and EGR System monitors are ‘not ready’

The Misfire, Fuel System, and Comprehensive Components monitors are all ‘Ready’. The ‘Oxygen Sensor Heater’ starts out ‘not ready’, and is the only Non-continuous Monitor that DOES transition to a ‘Ready’ state.

Are you sure you replaced the correct coolant temp sensor? There’s three of them. One for the PCM, one for the temp gauge, and one for the radiator cooling fans.


Where the heck is the sensor for the radiator cooling fans? I can’t find it in the shop manual, and when I ask at the auto parts store, they only list the one for the dash gauage (single spade conductor), and the one for the ECM (2 conductors). The dash sensor is in front of the distributor, and the ECM sensor is behind the distributor. Where’s Number 3?