I had a problem with the engine over heating on my '94 SL2. I traced it to the coolant/fan switch sensor which appeared to be doing nothing. I bought an after-market sensor and installed it. After starting the engine, the temp light came on steady, and the fan began to run immediately. I pulled the sensor again, checked the resistance across the pins and got a dead short, (Yes, I was very careful, being a trained electronics tech). Presuming it was bad, I went and got another one with the exact same results. Bad, too, I presume. I checked the connector and got good +5 volts on one socket, and good ground on the other socket. So, the PCM seems to be working fine. Thinking that I must be the victim of cheap Taiwan parts, I bit the bullet and got one from the Saturn dealer, and even asked him to have a tech check it, which he claims to have done. This time, I did not screw it into the block, but carefully attached the connector and left it loose. Started the engine and the SAME D**N symptoms. Yanked the sensor, checked it at the pins and again read DEAD SHORT CIRCUIT. O.K. says I, I run to my parts box, pull out a 2500 Ohm resistor, and a 250 Ohm resistor. These represent the top and bottom of the resistance range of the sensor which is supposed to go from around
5000 Ohms to 200 Ohms in range. I plugged the 2500 Ohm resistor into the socket and started the engine. All normal, no fan, richer fuel, no idiot light, so the PCM is doing what it's supposed to do. Repeated the experiment with the 250 Ohm resistor and sure enough, the fan comes on as it should, and no idiot light. So, gentle reader, WHATS WRONG????? Can all these sensors be bad? There seems to be nothing else left.Larry