Hi All,

I know the answer I am looking for must be in here somewhere, but my search skills are apparently lacking.

Here is the story:

My ’98 Maxima runs great despite the 316K on the clock and has only overheated once and that was after a catastrophic radiator failure. While stuck in traffic the other day Isuddenly noticed a lack of performance from the AC and then saw the temp gaugeat almost the top of the scale. I shutdown the AC, called for max heat and FINALLY got someone to let me out of the left lane so I could get to the breakdown lane and stop.

Suspecting another radiator failure I was surprised to find no coolant problems. While waiting for assistance, I realized the fans were not working. After the engine cooled down I started it and turned on the AC…Ah HA! No fans.

I let the engine cool completely, verified the coolant levelwas correct in the overflow and the radiator, then drove home (expressway travel) with no heating problems at all.

Apparently the fans will not come on under any condition (Temperatureor AC operation).

QUESTIONS: Does the command for Fan operation when AC is on come from the ECU to the Fan relays?
If I jumper relay 1from between pin 3 and 5 and the fans still refuse to run where could the problem be?
Is the Coolant Temp Sensor a possible factor given that the fans do not run while the AC is operating?

I’m stumped. ANY help will be greatly appreciated!

 

Coolant temp sensor gives info to the ecu, the ecu activates relays, the wires are terminal 13 and 14 on the ecu and are light green and light green with a red stripe. Chances are it is the coolant temp sensor so start there first(replacement). There is a way to keep the fans on with a little wire crossing in case of emergency, but don't try it if you are not good with electronics.

 

My fans recently decided to stop working on my 97 I30, same situation as what happened with you. I ordered a new radiator fan assembly from rockauto and it works great. After 316,000 miles I would expect it to stop working.

 

Try bypassing all the switches and sensors and apply power directly to the fan leads.

 

That is my current plan. The component test of the temp sensor indicates it is good; all resistance values are consistent with proper temperature readings. I have a new sensor, but it reads virtually the same as the old one when tested from the freezer and boiling water.
I completed all the diagnostic tests from the Service Manual, and they all indicate passed.
I cannot find the pin out for the connectors to the individual fan motors.
To which pins should 12 V be applied to make the motors run?

 

When things are working properly:

When you start the car and the engine is cold and the air conditioning is OFF, fans do not run. When the engine temperature reaches 200 degrees, both fans run at low speed. When engine temperature reaches 220 degrees, both fans run at high speed.

When you start the car cold and you turn the air conditioning ON, both fans run at low speed. When the engine temperature reaches 200 degrees, both fans run at high speed.

Pin 14 of the ECM goes to 0 volts, activating Fan Relay 1 which sends 12 volts to pin 1 of both fan motors, the low speed winding. Pin 4 of the motor is connected directly to ground.

Pin 13 of the ECM goes to 0 volts, activating Fan Relays 2 and 3. Fan Relay 2 controls fan motor 1, while Fan Relay 3 controls fan motor 2. The fan relays send 12 volts to pin 2 of the fan motor, the high speed winding. The fan relays also connect the fan motor pin 3 to ground.

On the fan motor connector: (4th gen colors)
pin 1 is a white with black stripe wire - low speed 12 volts
pin 4 is a black wire - low speed ground.
pin 2 is a white with blue stripe wire - high speed 12 volts.
pin 3 is a white with red stripe wire - high speed ground.

The ECM uses a water temperature sensor in the engine to determine when to turn on the fans. Also note that there are 2 water temperature sensors in the engine, one for the ECM and one for the dash gauge.

Dashboard fuse 17 powers the energizing coil of all 3 relays.
Underhood fuse D powers both fan motors at low speed.
Underhood fuse E powers both fan motors at high speed.

 

Great info! Just what I needed.
I found some really small test clips to make contact with the small pins in the fan connectors today. I'll investigate the fans tomorrow.
I am starting to suspect they have failed. I jumpered pin 3 to pin 5 in fan relay 1 today. No fan activity. My theory is that with relay 1 simulating energized they should have run at low speed...
Now that Dennis has given me the pin out for the connectors I will check the fans individually.
I'm betting one failed a long time ago and I just now discovered it when the second one failed.
Time will tell...

 

Can you spin the blades by hand and it moves freely or are they stiff?

 

I would say either bad fans or bad coolant temperature sensor. I have had to deal with both on 4th gen maximas. Just find out which one it is and replace it.

 

The blades spin freely, but one is "freer" than the other.

 

Fred, did you get to the bottom of this? My 96 maxima is the same. No radiator fan action at all. I can spin the motors/blades both hi and low speeds using my trickle charger and the previous pin out info. But nothing when I start the AC.
Did you end up replacing the water temp sensor? Any info regarding that is appreciated.