2002 impala cooling fans

[claytonduk]

Should the engine cooling fans come on when I turn the A/C on? Or does the engine have to be above a certain temp? My check engine light is on with a P0480 code and the fuses and relays are all good for the fans. Fans do not run when the A/C is turned on but I haven't let the car sit and get hot. when the car is off I can spin the fans manually. It's a 3.8L. Thanks for any help!

[maxwedge]

Code refers to low speed cooling fan circuit or relay, so check that out.

[claytonduk]

the chevy dealer i took it to said he checked the relays. this morning i let the car idle with the a/c on and after 5 min the fan on the drivers side came on for about 3 seconds and shut off. then it came back on after about 90 seconds for the same amount of time. not sure if the fan is fan 1 or 2. is the other fan supposed to come on at a certain temp?

[maxwedge]

Yes, at 222 degrees.

[claytonduk]

does anyone else have any other ideas as to what the P0480 code could be? I'm stumped.

[BNaylor]

Originally Posted by claytonduk

does anyone else have any other ideas as to what the P0480 code could be? I'm stumped.

The P0480 DTC is a cooling fan #1 relay circuit fault. The output driver in the PCM module has failed the electrical integrity test. First swap out the cooling fan relays with each other. There are a total of three relays used but work with number 1 and 2 only. If that doesn't do it them possibly bad PCM module or wiring between PCM and cooling fan # 1 relay.

[bozr]

I'm working on a 2000 3.4 with P0480 that's doing the same thing.
Nothing happens at 223 degrees. At 230 the left side fan came on at high speed for a few seconds. The right side fan felt a bit stiff when I turned it by hand so I pulled the assembly and hooked it up to 12v, the fan turned half a revolution and locked up solid, it's toast.
That's as far as I've got, the radiator is out for repair with a cracked side tank. I'll find out more in the next few days.

[bozr]

Update; It was the burned out fan motor and the fuse. Low speed fan comes on now at 217 degrees.

[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

[claytonduk]

thanks Bozr for your help! here's what I did so far to test. I unplugged the connection at the coolant temp sensor and started the engine. fan 2 came on at high speed but not fan1. with fan 2 running I swapped relays and both relays ran fan 2. I also unplugged the 25a fuses and swapped them and both ran fan 2. then I unplugged fan 2's connector and plugged it into fan 1 and fan 1 came on. so both fans work. in the fuse box the relay labeled 'fan cont 3' is a 4 prong, 'fan cont 2' is a 5 prong and 'fan cont 1' is a 4 prong. I swapped fan 3 relay with fan 1 relay. so I couldnt swap fan1 with fan 2. could this be a wiring problem or could it be the coolant temp sensor. the temp gauge is running a few degrees lower than it used to when the car was new. Thanks for any additional help!!

[bozr]

Great, thanks for posting back. I’ll have to edit my post to reflect the relay numbering in different years. Basically there are two 4-prong fan relays and one 5-prong mode relay.
The good part is that you have 2 good fans and 2 good fan relays. You can leave the CTS out of the picture for now. The first thing is to get both fans working.

It's possible if the mode relay had a burnt connection between 87a and 30. Although the dealer said he tested them. You may want to check if another vehicle has a 3602 relay you can borrow for a test.

Beyond that you’ll need a basic voltmeter to test the connections. There are a few things to check. I’d start with fan 1’s connector.
Engine off and the relays pulled. One terminal of the plug should have continuity to socket 30 in the 5-prong mode relay and the other to socket 87 of the fan 1 relay.
Socket 30 of the fan 1 relay should have 12v to ground.

I’d try checking those first. There could be a break in the wiring harness from the fan connector to the junction block.

[claytonduk]

thanks Bozr. I'll check those things out and post back. might be a few days. need to get a voltmeter.

[claytonduk]

Also Bozr I just replaced my BCM and the heated seats both worked before the replacement. now the drivers side has no heat. does the BCM control the heated seats. Fuse is good.

[j cAT]

Originally Posted by claytonduk

Also Bozr I just replaced my BCM and the heated seats both worked before the replacement. now the drivers side has no heat. does the BCM control the heated seats. Fuse is good.

why did you replace the BCM ? this needs to be programed for your specific vehicle .....

install the original BCM to recheck for the seat heaters working...

[claytonduk]

I replaced the BCM because the doorlocks stopped working and the ignition would not shut off. even after taking the key out I the heated seats would turn on if I switched them on . I took it to a local chevy dealer who programmed the new bcm which fixed both problems. but now the drivers side seat doesnt work. When I switch it on and off with the radio on I can here a static click thru the radio. Dont know if this means there is power at the switch or not. Also I did try putting the old BCM back in and the car wouldnt start.