2002 impala cooling fans

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!

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

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?

Yes, at 222 degrees.

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

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.

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.

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

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.


http://img716.imageshack.us/img716/7563/01impalafanrelay02.png (http://img716.imageshack.us/i/01impalafanrelay02.png/)

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

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!!

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.

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

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.

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...

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.

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.

most likely the heater seat switch , but could be the seat heater elements ...usually the switch gets worn out ...with a VOLT meter you can determine this ..

BCM failures are common with your vehicle ...

hey Bozr....I got a multimeter and pulled the 3 relays. I tested them for continuity between terminals 85 and 86 and all 3 read 75. I guess thats ohms? when I tested the 5 prong relay my meter flashed some numbers, beeped constantly, and dropped to zero. Is that normal?

Sorry Bozr the beeping was when I connected terminals 30 and 87A.

Yes, the 75 is Ohms of the coil. The beeping means there is continuity between 30 and 87a which is correct. Zero resistance.

Now that you can test for continuity, test the fan connector terminals to the socket.

I unplugged the connector to fan 2 and set my meter to 20v dc and put the neg and pos probes into the connector . the reading was 0. is this correct? Forgive me as I need hand holding when it comes to electricity.

You'll need to set the meter to test for continuity. It may say beep or have a sound symbol. In that mode, when you touch the meter's test leads together, it will beep and show that there is continuity between the two probes.

From there you'll want to test for continuity between the wires from the fan plug to the appropriate relay sockets. (All three relays pulled and ignition off)

For example. One of the conductors in fan 1's plug will have continuity to socket 87 in fan relay 1 , the other conductor to socket 30 of the mode relay.
87a should have continuity to one conductor in fan plug 2 and, fan 2 relay socket 87.
The other wire in the fan 2 plug should connect to ground. (ground symbol at G103)

Be a bit careful with the meter. don't check a hot (12v) circuit with the meter in continuity mode. Most meters have circuit protection but inexpensive meters may only have an internal fuse. If you're unsure, test for voltage first then test for continuity. Pulling both fan fuses out should help.

And yes, it can be confusing. Take it slow, study the schematic wire by wire.

Thanks Bozr for the info. I checked all circuits and they tested good. The only thing I am unsure of is the fan 2 plug to ground . what does 'ground symbol at G103' mean? where does the other probe connect to?

The body, engine and negative battery post are all Ground. Whatever you use, clean it off if it's oxidized.
After you've tested every socket terminal you can go on to test for 12v at each relay socket.

Remove all the relays and disconnect the CTS. With the engine running, (meter set for DC volts) there should be 12v between socket 85 and 86 at each relay socket.

I'll test those now.....another question, can I test the fuse sockets by pulling the fuse and probing each side?

Yep. Continuity test to the relay socket on one side. 12v to ground at the other.

ok I got a reading of 13.8 to 14.5 volts for all 3 relays. as far as testing the fuse sockets, since I have current in all the relay sockets there should be current in the fuse sockets right? also where do the probes go to test the fuse sockets. like I said I'm not up on the lingo!

is it also possible the mode relay is bad and its not switching on fan 1?

Yes.
If the mode relay doesn't switch there would be +12v at both terminals in the fan plug (running with CTS unplugged)

so where do i go from here ? do i replace the mode relay ? Bozr you've been very helpful believe me . I've been trying to look at the diagrams you sent and they r very helpful . It seems the wiring is good . maybe the mode relay or the CTS is bad ? should I try replacing either one?

The CTS is out of the loop when it's unplugged. Both fans should be on.

Hook the black probe on your meter to ground. Engine running, relays installed, CTS unplugged,
Use the red probe to test the plug connector at fan1. If it reads 12v from both wires, the mode relay is bad.

If only one wire has 12v, the other wire (White in the schematic) should have continuity to ground. If there is no continuity to ground, trace it back to find where it breaks. It should have continuity to socket 30 at the mode relay.

hey Bozr... just got done testing the fan 1 cable. with black probe on the neg battery terminal and red one in the connector I got a reading of .09 volts on one side and 0 on the other.when I checked for continuity I shut the engine off and pulled the mode relay. touching terminal 30 with the plug I got continuity only on the side that had the .09 voltage. no cont. on the other side and no voltage. bad relay mode?? I did notice that after running the engine and checking for voltage, when I unplugged the mode relay it was a little warm . the other relays were cool. It was noticably warm but not a big difference than the other 2.

I think I understand what you mean.
First, you don't have 12v from the fan 1 relay.
Did you test for continuity from the fan plug to relay 1 socket 87?
Does socket 30 have 12v to ground?

With the engine running CTS Removed
Fan 1 relay removed.
With a short piece of wire, temporarily connect socket 30 and 87. Does the fan come on.
You previously said you had 12v between socket 85 and 86. Check it again, engine running CTS removed.
Is there 12v to ground on socket 86?
Is there continuity to ground on socket 85?
If there's no continuity to ground on socket 85 either the wire connecting the PCM is broken or the PCM low speed fan circuit is burned out.

I did the test with the wire between 30 and 87 of fan relay 1 and the fan came on. Does that mean a bad fan relay or mode relay? thanks for your help once again!

actually I did swap relay 1 with relay 2 and fan 2 ran with both so I'm hoping its the mode relay. with CTS unplugged , engine on, and fan 2 running, should the fan shut off when I pull the mode relay? Because the fan stays on.

The mode relay and fan2 relay are fine. Relay1 is not energizing. Finish the test.

"You previously said you had 12v between socket 85 and 86. Check it again, engine running CTS removed.
Is there 12v to ground on socket 86?
Is there continuity to ground on socket 85?
If there's no continuity to ground on socket 85 either the wire connecting the PCM is broken or the PCM low speed fan circuit is burned out."

I just checked voltage between 85 and 86 on all 3 relays removed, engine running, CTS removed. 14.35 volts at fan 2 relay and mode relay. fan 1 socket started at 14.xx volts and gradually dropped in increments of .03 or .04 volts until it settled at 7.13. dont think I had this happen before.

Ijust checked voltage between all 3 relays with engine off and got 12.53 on all 3. with engine running and only relay 1 removed I got .17 volts to ground between 85 and 86. no continuity to ground on 85.

You'll have to test fan1 socket 85 for continuity or an intermittent connection to the PCM connector inside the air cleaner box.

I don't have an end view so I'm not sure about the pin-out on the PCM connector.
You'll need to remove the connectors from the PCM.
The schematic shows a (dark green) wire at pin 6 which (looking at the C1 connector) would be the sixth pin starting from the bottom lower left.

thanks bozr. I'll check those out in the AM. Gotta go to work, YAY!

One thing before I leave for work. Why did fan 1 come on when I jumped 30 and 87 on fan1 socket?

When the relay is energized at 85/86 it connects pin 30 and 87.

hey bozr, I have the pcm visible but am unsure how to remove the connectors. there are 2 screws holding a plastic cover on but there is also a red clip on the left side where the 2 wiring harnesses go in. connectors are not visible . do I remove the 2 screws on the plastic cover?

hey bozr you were right on. I took the 2 connectors off and checked the sixth pin from the left on the bottom connector on the bottom row and at first didnt get continuity. but as luck would have it. I must have moved the connector the right way and I got a beep!! It connects to socket 85 of fan relay 1. only problem is when I move the connector the slightest bit I lose cont. But I can get cont. if I hold the connector in a specific position. So I'm thinkin the wire problem is in the connector or in the wiring right near the connector.

oh well it seems I was wrong but that could be a good thing. It turms out the probe on my meter is too thick to make good contact in pin 6 so I wrapped a paper clip around it and got constant cont. no matter which way I moved the connector. Now what do I test?

Well that's not good. That would mean the PCM may be bad.

But first.

After rereading your previous posts;
Did you you test for voltage from 86 to ground?
Did you test for continuity from 85 to ground? (Engine running CTS removed)
Testing between 85 and 86 doesn't tell whether it's the positive or negative side that's missing.

I'll retest those now. puttin 'er back together......

another thing I never mentioned. The wiring harness to the CTS had another connector on top of the engine so I've been disconnecting it from there because of easier access. There are no other wires other than from the CTS . Does this section have to be tested for cont?

It may not matter as long as fan 2 is still coming on but I would disconnect at the CTS for the last few tests to be sure.

all back together . engine running cts removed. I did check cont on the section of cable going to the cts and there was cont on both wires. I checked volts between 85 and 86 on fan2 which was 14.35. between 85 and 86 on fan 1 the volts started out at 14 and steadily dropped down to 2 or so. 85 on both sockets to ground was 14.35. ther was no cont to ground on both 86 sockets . sounds like a ground issue

There would be no continuity to ground on 86 because it's hot. Does your meter still work.

Fan 1 relay socket
Test for voltage from 86 to ground?
Test for continuity from 85 to ground? (Engine running CTS removed)

85 on all 3 relays has 12.35 volts to ground with engine off and 14.55 volts to ground with engine on cts removed. 86 on fan2 and mode relay had a 37 reading for cont. fan1 socket 86 had no cont to ground. 85 is hot 86 is ground.

Ok, that helps. Are the socket terminals marked with B8, C8, C10 and B10?

What's missing is the ground signal from 86, without that, relay 1 doesn't energize. Since you have already tested continuity to the connector the fault points to the PCM.

Before you get a replacement PCM you may want to take it to the dealer. The fans can be commanded on with their scan tool to be certain it’s a bad module.
Also, I'm not sure, a replacement PCM may need to be programmed to your VIN. Someone here might have more info on that.

ther are no markings on the sockets . the relay itself has 30,85,86,87. I still haven't tried replacing the mode relay . But you did say that was good .

also is there a way to check ground from pcm to relays like I did for cont from pin 6 on the pcm to socket 85?

You can jumper the fan1 relay at sockets 30 and 87 with the engine off. Both fans should come on in low-speed mode. That would test the fan grounds.

The ground that you don't have is the one from the PCM that energizes the coil in relay1 and then connects 30 and 87.

can I test the ground from the pcm like I did with pin 6 to socket 85?

Pin 6 to fan1 socket 86 was the ground connection to the PCM.
You already tested the continuity in the wire going to the PCM, right?

The PCM controls the ground to socket 86.

sorry yes that was continuity from pin 6 of pcm to socket 85 of fan 1 relay and it was ok.

oh yeah I went to autozone and got a new mode relay . I was going to put it in at the store but didnt have plyers to take the old one out. check engine light was still on but as I was driving the check engine light went out. So when I got to my next destination I kept the car running and disconnected the CTS and still only fan 2 came on . I shut the car off and when I started it again within a few miles the check eng came on again. when I got home I swapped the old mode relay with the new one and still only fan2 came on. oh well it was worth a try.

hey bozr....remember how you had me jump 30 and 87 with a small wire? Is there any way I can jump the terminals to get the check engine light to go off long enough to get it to pass inspection?