Since i've had my car, the fans would start when i would turn the key on. i decided to replace some broken stuff.. and make it original. It is an Iroc-Z 305 tpi with dual fans from factory. Seems like someone broke the mushroom cap from the switch fan. also, they jammed the metallic connector so it would ground inside the switch. i got a 4 seasons switch that lets the secondary fan go on at 212 degrees Fahrenheit (100 degrees C). Also got a new pigtail for the switch (same as the knock sensor).






Then, one of the relays was bbq'ed, so i got one from BWD. i let the engine warm up till 125 degrees C and no fans turn on. Now, if i ground the pigtail from the switch fans, both fans turn on (when car is hot). If the car is cold, only the secondary fan turns on when i ground the pigtail. This tells me that the ecm is reading the coolant sensor.




Also, i checked the resistance of my coolant sensor and it was within the resistance for the temperature that it was at. After, i checked the voltage from the connectors for the relays. i notice the F voltage wasn't right at all in one of the connectors.

Connector for relay (primary fan)
A= oV
E= 11.53V
D= 11.44V
F= 0.04V


connector for relay (secondary fan)
A= oV
E= 11.53V
D= 11.40V
F= 11.26V

After i went to check the connection of the ECM. I grounded the green and white wire at the ECM connection and the primary fan turned on. Then, i grounded the gray wire for the secondary fan and it turned on.

Note: when i disconnect the ECM connection, The F reading voltage at the relay for the primary fan is 11.26 volts. I connect the ecm to the connection and the voltage drops to 0.04volts. To have an idea, the following picture is the connection for the ecm where the green and white plus the gray wire are.




Anyone have had a similar problem? All sensors, relays and connections are in good shape as you seen. My question is, could be the ECM that doesn't ground the fans anymore?

 

Have you tested/replaced the coolant temp sensor in the intake? That's the one that tells the ECM the engine temp, and thus the ECM turns on the primary fan (which is factory set at about 218*F). That sensor has 2 wires, one black and one yellow.

 

thanks for the reply. i checked the resistance and it was fine numbers. i was thinking, make the ECM read the engine is really hot by only jumping the coolant sensor pigtail with a resistor. if it reads the engine is really hot, the primary fan should turn on.

ps- just finish testing the ground on the ecm. It has ground like in the whole body.