Coolant fan is driving me crazy!!!!

[s10surfer]

I have a 1996 Pontiac Grand Am SE with the 2.4L and Automatic Transmission. 171,000 miles.


I am having a difficult time getting the radiator coolant fan to work properly. The fan is not coming on under normal operating procedures. The fan will not come on when the AC is turned on and the fan will not come on when it reaches warm temperatures of proximity 220 or above.


So fare I have replaced the fan fuse, the fan relay, the coolant fan thermostat sensor, the air temp sensor, both O2 sensors, the radiator, the upper and lower radiator hoses, the coolant exit adapter coming from the top of the block, and the engine thermostat. On another note I have also replaced the spark plugs, and ignition modules plastic housing.

I cannot think of what else to check to get the fan working. I have wired the fan directly to the battery using jumper cables and the fan fires right up, so I know the fan motor, and assembly works. I also noticed that during an event that causes the service engine soon light to come on, the fan will turn on and remain on during any operation of the vehicle. Once I clear service codes the fan will go back to being nonoperational. This problem is really driving me crazy and I have spent a lot of money at it so fare. Does anyone have any ideas of what else I can try or test? Thanks for any help.

[xeroinfinity]

Welcome to AF !

This 96 have one of two cooling fans?? i forget...

If it has two then thiers two relays, also check the grounds for the fans & relay(s)

Also what code(s) sets the fans to constant "on" ?.

[s10surfer]

Hi, thanks for helping me out. On the 96 model there is only one radiator fan and relay. I traced the fan positive cable back to the relay at the firewall on the passenger side of the engine compartment. I ran a jumper cable to this point where the relay would normally provide power and I left everything else as is. As soon as I jumpered power directly from the battery it turns on. The relay has two positive power points that are on all the time, and are colored red. It has a smaller green cable that may come from the Cars PC but I’m not sure. The fourth cable is blue and runs power directly to the fan. The green cable has 0 volts with the car turned off, and has .14 volts with the car turned on and the ac on. I’ve been using the ac to test the radiator fan because the fan should turn on as soon as the ac is turned on. The two red cables have between 12 and 14 volts depending on if the car is running or not. I have tried two new relays and both have provided no new results.


The fan was automatically turned on when I received an engine code of P0420, which is catalyst system low efficiency. I had previously replaced the O2 sensor at the manifold but not past the cat. According to AllDatad the fan will turn on if this code is present, which it did. After I replaced the O2 sensor after the cat and cleared the code, the fan stopped working again. Is there a way to test if the on board computer is sending the correct signals to the relay. Any idea what the volt reading from the green cable going into the relay should be. The ground at the fan is good. Should there be a ground at the relay? Like I said there is two red power cables, the green cable that may be a power or signal cable, and then the blue power cable running directly back to the fan. Thanks for any ideas or help.

[s10surfer]

Ok I took your hint on the ground and looked at the relay and wiring again. Looking at the basic way a relay operates I took the relay and some jumper cables and hooked it up to the battery. I then took the pin where the green cable is wired to and grounded it. The relay immediately clicked. I then took a volt meter and check the pin that would lead to the positive side of the radiator fan. The pin showed proper voltage. I next took the relay with jumper cables and connected it to the original wiring harness. I did this so I could back probe the pins. As usual when I tuned the ac on nothing would happen. I then took another cable and grounded the pin where the green cable attaches to and the fan turned on. From what I have seen the green cable is the ground to close the loop on the relay. I would guess that the cable should ground out if the temp gets too high or if the ac is turned on, the problem is the cable is not grounding out, during ether circumstances. So now I need to figure out where this green cable goes and if it goes directly to the pc. If it does go directly to the pc does this mean I should replace the pc in the car next? Once again thanks for any help.

[xeroinfinity]

The dark green wire goes to the PCM this could be your troubles , check it for cracks/breaks back to the PCM. The # on the PCM where this green wire attaches is C2 - 54.
Also you might double check the wires to the temp sensor and test that voltage is present and that thiers no cracks or breaks..

Ok on the p0420 I would change the O2 after the Cat, thats most likly whats causing the dtc. And could be another reason why the fans not working.


Hope that helps!

[s10surfer]

Right after I pulled the P0420 code I replaced that O2 Sensor with a new one and cleared the DTC. It has not come back since I replaced the O2 sensor. I will check the tep sensor at the block with a back probe; I believe it should be 5 volts. I will also trace it back to the PCM and I will check for proper voltage entering the PCM. I will also trace out the green cable and will check for the things you listed. I also planned on using an ohm meter on the green cable to check for good connectivity all the way to the PCM.

One thing; Form the diagrams I pulled from AllData, the diagrams showed the green fan cable going to C3 12 on the PCM plug. I will just completely trace it out. It also showed the cars speed sensor hooked up as part of the engine fan relay switch. It at least displayed it in the diagram with the PCM and the coolant fan relay, and wiring.

One more question, do you know where the PCM is located in the car? Thanks for the ideas, I will see what happens.

[doctorhrdware]

I know in the gp the pcm is in the air filter box, Ibelieve that the ga is in the same location.

[xeroinfinity]

Originally Posted by s10surfer

Right after I pulled the P0420 code I replaced that O2 Sensor with a new one and cleared the DTC. It has not come back since I replaced the O2 sensor. I will check the tep sensor at the block with a back probe; I believe it should be 5 volts. I will also trace it back to the PCM and I will check for proper voltage entering the PCM. I will also trace out the green cable and will check for the things you listed. I also planned on using an ohm meter on the green cable to check for good connectivity all the way to the PCM.

One thing; Form the diagrams I pulled from AllData, the diagrams showed the green fan cable going to C3 12 on the PCM plug. I will just completely trace it out. It also showed the cars speed sensor hooked up as part of the engine fan relay switch. It at least displayed it in the diagram with the PCM and the coolant fan relay, and wiring.

One more question, do you know where the PCM is located in the car? Thanks for the ideas, I will see what happens.

I wasnt exactly sure on the pin location on the ECM(PCM) just from memory. Its the only green wire in that area of the computer.
If you have a Alldata then you should know the ECM/PCM is on the right side[/color][/url]. And no its not in the air box like the GP's.

[krklinegvr4]

Figure I would throw you guys an update.

Tested the AC fan by turning on AC. Fan wont turn on. Ended up having a bad fuse. (red small fuse) So that fan now works only when AC is turned on. Ended up replacing the engine thermostat sensor. I guess it was reading to low. Both fans kick on now.

Only one issue is fans kick on at 215 degrees. Seems kind of high. Going to hook up scan tool and see what temperature the ECU is seeing. Maybe dash gauge is off.