There are three relays in the underhood electrical center. They are directly controlled the the PCM. The PCM gets it's information from the coolant temp switch that is on the engine. On the PCM, Pin 54(dark green wire) in connector C2 controls the ground to the relay 1. Pin 59(dark blue wire) on the same connector controls the ground to relay 2. If you supply a ground to these, you will turn the fans on. What you need to figure out is if the ECT is telling the PCM what the temp is, (more likely cause) or you have a PCM malfunction(least likely cause).
Testimonial: "You didnt mention the 3rd relays function? What IS the FAN MODE RELAY suppose to do? And what scan tool do I need to find out if the ETC is telling the PCM the temp.? I have access to an ODBII and that's about it. People are telling me to put a switch in dash to turn them on manually,but wont that confuse the PCM further?"
SOURCE: Torque Spec for '99 Chevy C1500 5.7L engine lower intake manifold
On 5.7L engines, install the bolts and torque in sequence as follows:
SOURCE: Electric Radiator Fan Does Not Come On
DTC P0480 - COOLING FAN CIRCUIT
Circuit Description
The cooling fan is controlled by PCM through the fan relay based on inputs from ECT sensor, IAT sensor, A/C selector switch, A/C refrigerant pressure switch and vehicle speed sensor. PCM controls cooling fan by grounding cooling fan control circuit which turns on cooling fan relay.
The fan relay will be commanded on when ECT reaches 223°F (106°C) or greater, A/C is requested or vehicle speed is less than 38 MPH. Cooling fan relay will also be commanded on regardless of vehicle speed when a DTC is set requesting cooling fan to be on, ECT is 304°F (151°C) or greater, or A/C refrigerant pressure is high. Cooling fan may also be commanded on when engine is not running, on certain conditions.
Conditions for setting DTC:
Battery voltage greater than 9.5 volts.
Cooling fan fault line detects a malfunction for 6 seconds.
1. Check the cooling system. Ensure coolant level and belt tension are correct. Adjust/repair as necessary. After repairs, go to step 23). If no adjustment or repairs were required, go to next step.
2. Turn ignition on, with engine off. Using scan tool, check if cooling fan is operating with ECT at less than 209°F (98°C). If cooling fan is off, go to next step. If cooling fan is on, go to step 4).
3. Command cooling fan relay on. If cooling fan operates, go to step 23). If cooling fan does not operate, go to step 5).
4. Turn ignition off. Disconnect PCM harness connector. If cooling fan turns off, go to step 23). If cooling fan does not turn off, go to step 6).
5. Disconnect cooling fan relay harness connector. Using a test light connected to ground, probe battery feed circuits in relay harness connector. If test light illuminates on both terminals, go to step 7). If test light does not illuminate on both terminals, go to step .
6. Disconnect cooling fan relay harness connector. With test light connected to ground, probe battery feed circuit in relay harness connector. If test light illuminates, go to step 9). If test light does not illuminate, go to step 10).
7. Connect a jumper wire between cooling fan relay battery feed and cooling fan battery feed circuit. If cooling fan operates, go to step 11). If cooling fan does not operate, go to step 12).
8. Repair open in battery feed circuit. After repairs, go to step 23).
9. Repair short to voltage in cooling fan battery feed circuit. After repairs, go to step 23).
10. Connect test light battery voltage and probe cooling fan control circuit. If test light illuminates, go to step 13). If test light does not illuminate, go to step 21).
11. Connect test light to battery voltage and probe cooling fan control circuit. Using scan tool, command cooling fan on. If test light illuminates, go to step 14). If test light does not illuminate, go to step 15).
12. With jumper wire still connected, disconnect cooling fan harness connector. Using test light connected to ground, probe cooling fan battery feed circuit. If test light illuminates, go to step 16). If test light does not illuminate, go to step 17).
13. Repair short to ground in cooling fan control circuit. After repairs, go to step 23).
14. Check terminals to cooling fan relay. Repair as necessary. After repairs, go to step 23). If terminals are okay, go to step 21).
15. Check cooling fan control circuit for open or poor connection. Repair as necessary. After repairs, go to step 23). If circuit or connection is okay, go to step 22).
16. Connect test light to battery voltage and probe cooling fan ground circuit. If test light illuminates, go to step 1. If test light does not illuminate, go to step 19).
17. Repair open or poor connection in cooling fan ignition feed circuit. After repairs, go to step 23).
18. Check for poor connections at cooling fan harness connector. Repair as necessary. After repairs, go to step 23). If connections are okay, go to step 20).
19. Repair open or poor connection in cooling fan ground circuit. After repairs, go to step 23).
20. Replace cooling fan motor. After replacing cooling and motor, go step 23).
21. Replace cooling fan relay. After replacing relay, go to step 23).
22. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
23. Turn ignition on, with engine off. Command cooling fan on. If cooling fan operates, system is okay. If cooling fan does not operate, repeat step 1).
SOURCE: 2002 malibu runs hot.
Sounds like you have a faulty head gasket or maybe a cracked head.This can cause overheating and the check engine light to come on.The code for the o2 sensor is probably caused by coolant getting into the exhaust system and coating the sensor.The coolant fan may work but it cannot remove enough heat from the rad to make the engine cool off.Try some engine coolant stop leak to see if it will help.This maybe only a temperary fix.Let me know if you need more.MOE
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