2002 impala cooling fans

[bozr]

I imagine the PCM throws the code because it sees an out-of-range current in the circuit to the fan1 relay and that's controlled by transistors (quad driver) in the PCM.

One possible way would be if the engine never got to 217 degrees it might not be able to set the code. So, If you jumpered the fan1 relay at 30 and 87, both fans would run all the time in low-speed mode and most likely never get above 200. Disconnecting the battery may clear the code. Just a thought.

[murphyslaww]

First of all, Thanks bozr for posting all you have here. It's invaluable.

The car is an 02' Impala, with the 3.4 engine.

I'm having a similar issue. Code 0480. I am getting zero volts across socket 85 in the relay panel, and no fans are running. We were getting the drivers side fan to run on high from time to time, but now there is nothing.

Also, I am a bit confused as to where on my car, the CTS sensor would be. It doesn't seem to be anywhere near the water pump, but there is a black, square device that takes the lead from the passenger side fan and appears to be some sort of sensor going into the radiator a few inches below the radiator cap.

I also did check for continuity to ground from the passenger side fan connector, and it was good. Haven't checked the drivers side fan. Which one is fan 1, and which is fan 2?

No voltage to the relay panel would lead to what conclusion? I'm reading through everything else here and my answer my own question, but I'm hoping to get this solved fast, as the wife is working for the Census and needs this car back.

Thanks for any info.

*** EDIT *** I picked up a Haynes manual. (just about a waste of time for the 3.4, as there is little coverage of the 3.4, picturewise), and was able to find the PCM. It's in the airbox. With the way this car was treated before we got it,(maintenance was done, but it had a rough life) I can imagine it got wet up in there, but I'd guess the PCM is sealed? Anyway, my logic from bozr's posts lead me to a bad PCM. I think I found the CTS, and am going to disconn. it and see if the fans will kick over to high, and check voltages/grounds then at the relays.

Originally Posted by bozr

Here’s some info and observations that may simplify the cooling fan circuit and help out the next victim.
Basically there are 3 relays, two 4-prong fan relays and one 5-prong mode relay.
2001 on up markings. (?)
FAN CONT #1 - Primary Cooling Fan
FAN CONT #2 - Cooling Fan Control Relay (5-prong)
FAN CONT #3 - Secondary Cooling Fan


The fans have two modes, when energized both fans come on at either low-speed (serial connection) or high-speed (parallel connection).
The PCM controls the modes by grounding the coil in relay 1 for low-speed.
Or;
All 3 relays for high-speed.
For low-speed, relay 1 is energized and 12v is fed to the B-side of fan 1. The A-side of fan 1 connects to the B-side of fan 2 through the dual-throw mode relay. Both fans are in a serial connection.
In high-speed, the mode relay switches fan 1’s A-side to ground and relay 3 energizes fan 2. Both fans are in a parallel connection.

Terminal 85 of each relay socket should normally be hot. Terminal numbers are marked on the relay. Check the cooling fan fuses. Check the relay sockets for burned or bent terminals.
If there is no continuity in one of the fans (worn brushes or a bad connection) neither fan will come on in low-speed mode.
In low-speed, the fans are barely audible. In high-speed, the fan/s can be heard 30’ away.

A couple tests to start with;
Remove the fan1 relay and use a short piece of wire to jumper the terminals 30 and 87. Both fans should come on in low-speed mode.
The second is is to pull the connector off of the Coolant Temperature Sensor at the thermostat housing, then start the engine. After a slight delay of about 30 seconds, with no measured resistance, the PCM assumes the sensor has failed and turns both fans on in high-speed mode.

Swapping sockets can test relays 1 and 3. If one fan still doesn’t run, turn the engine off and check the motor for resistance and the connector for continuity to it’s relay terminal. One terminal of the fan 2 connector should have continuity to ground, the other to relay 2 socket 87a and relay 3 socket 87.

With the CTS connector removed, remove all three relays and start the engine. Again after a slight delay, there should be 12v between terminal 85 and 86 at all three relay sockets.
If not, check for +12v at terminal 85 to ground and continuity to ground on the 86.
No ground signal could be a bad connection to/or the PCM.
Whether terminal 85 or 86 is used for +12v could change between year/model. If yours is different from the schematic make a note of which terminal to check for a ground connection from the PCM.

Each relay should have resistance between the coil terminals 85 and 86 (around 80 Ohms.)
The mode relay normally has continuity between terminal 30 and 87A.
When energized, it should have continuity between 30 and 87.

The temperature that the PCM energizes the fans may be different between model/years. On this one, a 2000, the scanner shows the low speed circuit energize at 217 degrees and high-speed at 230.

When the PCM energizes the fans it sets a timer. For example, when the temp was at 228 it bounced up to 230 for a split second but the fan remained on for several seconds. This was at 40 degrees ambient; it may be different on a 90-degree day.

Turning on the A/C may or may not turn the fans on, it depends on system charge pressure and whether there’s a temp sensor in the circuit.




CTS resistance values

212F--177 Ohms
194F--241 Ohms
176F--332 Ohms
158F--467 Ohms
140F--667 Ohms
122F--973 Ohms
113F--1188 Ohms
104F--1459 Ohms
95F---1802 Ohms
86F---2238 Ohms
77F---2796 Ohms
68F---3520 Ohms
59F---4450 Ohms
50F---5670 Ohms
41F---7280 Ohms
32F---9240 Ohms
23F---12300 Ohms
14F---16180 Ohms
5F----21450 Ohms

[Sammyls24]

I have an 01 impala, After start up and turn off Hot or cold low speed fan runs. its 12 degrees right now and start car let run 2 seconds and shut off fan runs.. I swapped relays 1 and 3 to see if low speed fan was charged and sticking, No change in habit, Any Ideas?

[j cAT]

Originally Posted by Sammyls24

I have an 01 impala, After start up and turn off Hot or cold low speed fan runs. its 12 degrees right now and start car let run 2 seconds and shut off fan runs.. I swapped relays 1 and 3 to see if low speed fan was charged and sticking, No change in habit, Any Ideas?

fans should not be on with 12 deg f air temp engine on or off. the coolant sensor must be defective.

[Sammyls24]

Im aware its abnormal, thats why im here. I dont wanna grocery cart repair this.

[j cAT]

Originally Posted by Sammyls24

Im aware its abnormal, thats why im here. I dont wanna grocery cart repair this.

what I was saying is take the sensor out and test it. make sure the resistance is correct to temperature.

for 20.oo some would just change it because 11 yrs is when these items go wacky , and this effects the fuel mangement as well.

many times they will report a temp of 40 below when it is worm out the result is excess fuel and poor start..

in your case they will burn out the fans motors..

[Tech II]

What is the temp gage in the dash showing when this happens?