Where fare the relays for cooling fan on 86 cadillac

DTC P0480: Cooling Fan Relay 1 Control Circuit
Circuit/System Description
The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.
In low speed operation, the ECM applies ground to the coil side of the low speed relay. Voltage is applied directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay, which is the FAN CNTRL relay, so that both fans operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the low speed relay, the series/parallel relay, and the high speed relay. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed relay and ground through the series/parallel relay.
When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage. If the ECM detects that the actual voltage of the relay control circuit is different than the expected voltage, DTC P0480 or P0481 will set and the affected ECM driver will be disabled.

Conditions for Setting the DTC
• An improper voltage level has been detected on the cooling fan relay control circuit.
• The condition must be present for a minimum of 30 seconds.

Circuit/System Testing
Ignition OFF, disconnect the 3 cooling fan relays listed below.
• FAN LO relay
• FAN CNTRL relay
• FAN HI relay
Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 85 of each relay and ground.
? If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
Verify that a test lamp does not illuminate between the ignition circuit terminal 85 and the control circuit terminal 86 of each relay.
? If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM.
Remove the test lamp.
Ignition ON, command the affected relay ON using a scan tool. Verify the affected scan tool FC Relay Control Ckt. Short Volts Test Status Parameter is OK.
• For the FAN LO relay, use the scan tool Fan Relay 1 command.
• For the FAN CNTRL and FAN HI relays, use the scan tool Relay 2 and 3 command.
? If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Install a 3A fused jumper wire between the control circuit terminal 86 and the ignition circuit terminal 85. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status Parameter is Fault.
? If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits and the ECM test normal, replace the affected relay.

There is a cooling fan relay in the under hood fuse / relay box . There is a fuse F1.8 20amp in the same under hood fuse / relay box ! If you pull the relay out of it's socket an look on the bottom you'll see some numbers , 30,87,85,86 ! 85an 86 are the control side of the relay an 30 an 87 or the load -fan side ! If you take a test light or volt meter you can check for battery voltage at pin 30 ,you could take a jumper wire from pin 30 to 87 an the fan should run , if the fan motor is good an there is battery voltage at pin 30 ! Pins 85 an 86 are the control side of the relay ,pin 86 should have battery voltage an pin 85 is from the engine computer ,when the temperature get's to 195 - 213 degrees the engine computer will ground pin 85 through a transistor inside the computer energizing the relay turning on the cooling fan ! You can test right there at the relay ! VEHICLE RELAYS Operation Diagnosis

Check fuse for cooling fan, check temperature sensor functioning for cooling fan, check relay for the fan (if you have one), check cooling fan motor circuit with resistance check (should read low Ohms, less than 2 Ohms beacause the fan is a powerful motor with 10-20 Amps).
If everything is measured O.K. you should check the wiring. Disconnect the connector at the cooling fan motor, connect a test light to the harness from the car (not to the motor side) and run the engine. Watch the temperature gauge and before you the boiling (overheating) the bulb should lit up. If not you should go back with this test step by step to the relay. The relay can be tested if you can find a same one on your relay board and swap temporary (e.g. swap the AC clutch relay with the cooling fan relay)

radiator fan sensor faulty. the sensor opperates at certain high temp to switch the cooling fan on.

The diagram is a little hard to follow, but it looks like on the high fan relay there are 5 circuits like on the hi-low relay.
Pin 86 is power for the magnet, 85 is the ground signal from the module. The module grounds the magnet to move the contacts.
Pin 30 goes to the fan and pin 87 goes to a 50amp fuse.
Pin 87A is a jumper between the two relays.
The fan motor gets power from three different sources and is grounded to the car. The other two wires are return signals to the module. Kind of like a three way light switch in a house.
On the fan control relay, pins 30 and 85 are hot, pin 87 goes to the fan motor, and pin 86 is grounded by the module.
I can send you the diagram in a separate message if you need to see it.

This is controlled by a cooling fan sensor/temperature sensor, as well as fuses, and a relay. These will have to be checked.

Make sure your coolant level is full, the coolant temperature switch won't work if the level is too low. If coolant is low, you need to find out where it went to by pressure testing the cooling system.

If it's not low and the fuses are good, the relay is working:

The fan should be tested, bypassing any sensors to make sure it is functioning properly.

The sensors can be tested to be sure they are working properly at the correct temperature with a voltmeter/ohm meter.

Reverse troubleshooting the wiring and ignition is the next step if you haven't found the problem.

Good luck !

CHECK MODE RELAY IF BOTH RELAYS GOOD YOU CAN CHECK RELAY BY REMOVING IT FROM FUSE BOX HOOK RELAY TERMINAL 85 TO BATTERY POSITIVE AND GROUND TERMINAL 86 IF CLICKS RELAY GOOD. IF RELAY GETTING POWER GOOD AND THE 30 AMP COOLING FAN FUSE OKAY.EITHER THERE IS A SHORT IN COOLING FAN WIRING OR THE PCM HAS FAILED.THE PCM HAS LOST OR COMMAND RUN CIRCUIT IN PCM SHORTED OUT DUE TO PCM FAILURE.LET DEALERSHIP OR GARAGE USE DIAGNOSTIC EQUIPMENT TO ACTIVATE THE PCM SEE IF IT HAS FAILED.DONT SPEND MONEY ON NEW PCM COULD BE SHORT IN THE WIRING CIRCUIT

On the relay you should have 12 volts at 2 slots terminal 30 has power all the time terminal 86 has power when then computer tells the relay to turn on fan, for cooling or a/c, terminal 85 is ground(-) for the 86 terminal to energize the relay to send 12volt from terminal 30 thru relay and out terminal 87 going to fans, sounds to me like computer not getting the signal to relay, you did get for blow fuse? and does fans come on with a/c on?

Hi, Did you check the thermostat. If the thermostat is stuck and will not open properly, the fan will not come on. Have it checked out. Good luck.

There are three cooling fan relays in the fuse block under the hood.




The fan relays above are numbered 37,39 and 40

Relay 37 is RH fan
Relays 39 and 40 are LH fan.


You can check if your fans are working by switching on the air con.
Are you having overheating problems?

Regards.