When someone sits on the passenger seat, at first the light showing that there is a passenger in the seat turns on and then off. The seat belt sign stays off all the time.
All this time, I didn’t think the Occupant detection module under the passenger side could be bad because the terminals looked so clean. Running out of ideas, I decided to open it up, knowing very well that if I mess up I might have to shell out about $250 for a new module. Upon opening it, I think I found one of the problems related to the srs light being on (there could be more). There was heavy corrosion on the circuit board even though the male connectors were sparkling clean. I am going to see if I can find one from a junkyard. I am thinking that I might have take it somewhere and re-calibrate it too.
For all Corolla owners, here is a warning. Apparently, this occupancy detection system is extremely prone to moisture damage and unfortunately it sits low, closer to the floor. There is some kind of rubberized coating on the circuit board (which I haven’t seen in the ECU or SRS modules that I have opened up so far), which means that Toyota knows very well that this module will have moisture entering it. But that coating is not good enough to provide moisture damage protection. Most washing machine circuit boards are embedded in some kind of hardened resin to protect them from moisture entering them (at least the ones that I have seen). Compared to that Toyota is doing an extremely poor job at protecting this circuit board.
Next time, I am putting a bead of silicone along all possible entry points for moisture or at least putting a plastic bag and taping it up.
About the seat belt latch, I did not measure any difference in resistance when the latch was on or off, making me think that it could be faulty. However, I could just be assuming that it is faulty. The last thing that I want to do is to throw parts at the problem, hoping that something will fix it.
So far, my conclusion is that the occupancy detection module is definitely faulty and the passenger seat belt latch might be faulty. I am still not sure about the seat belt latch. There is no sign of damage or corrosion even on the circuit board. Could it be that the seat belt sign is not coming on because this module under the seat is bad? or is that an entirely different system? I will try to replace those and see what happens. At least the srs module is communicating to give me an error code (previously, the srs readers weren’t able to communicate with it).