2000 Venture - code P0480

Service Engine Light has been on for a while now but with emissions inspection due soon, I finally decided to fix the problem. Before I even checked the code, I knew it had something to do with the cooling fan because it wasn't kicking in until the temp gauge was up to about the 3/4 mark. Anyhow, the code reader came up with P0480 (Cooling Fan 1 Control Circuit)

Here's what I've done to troubleshoot so far:

- switched the the relays to see if the code would change to P0481 (Cooling Fan 2 Control Circuit)...it didn't. That would seem to indicate that both relays are OK. For the heck of it, I pulled the relays from my wife's Grand Am & tried them...there was no change.
- hot wired each fan one at a time to confirm they both work...they do.
- pulled the plug from the temp sensor in the intake manifold near the thermostat housing...passenger side fan came on almost immediately, driver's side did not. Pulling the plug added P0118 (Engine Coolant Temp Sensor High Voltage) to the code list. Since I didn't get the sensor code until I unplugged it, I'm guessing it's OK.

I did a lot of searching on this. Found a lot of people asking the same question but I didn't find an answer. I'm leaning toward replacing the thermostat, but I'm not sure if it's the problem therefore it might not be worth the hassle. The part is cheap enough, but it looks like a pain in the butt to get at.

Anyone got any other suggestions? Thanks.

Here's an update. I'm just tested the coolant temp sensor as per the instructions in the Haynes manual.

- I started by disconnecting the plug from the sensor, then used a multimeter to check the voltage at the plug. Turned the key to 'on', then checked the voltage...it was 4.98v. Should read 5.0v but I'm assuming my meter is slightly off, go I'm gonna consider the reading to be good.

- I then probed the pins on the cooling sensor for resistance with the engine cold. A chart is provided in the manual. With the outside air at 50F, the resistance should be 5670 ohms, at 58F it should be 4450. It's actually about 52F & my reading was 5550 ohms, so it should be OK.

- next step was to get the engine up to normal operating temp & test resistance again. The chart lists 240 ohms at 194F & 176 ohms at 212F. Of course, the temp gauge isn't numbered so I had to take a guess. I'm considering the 1/4 point (which is where it normally ran before I started having problems) to be about 195F. I ended up waking away for a little too long & when I came back, the temp gauge was at the 1/2 way mark. I took a reading & it was 206 ohms. I left the meter connected & waited til it rose to about 232, then disconnected it & reconnected the sensor plug. I fired up the van & the temp needle dropped to slightly above the 1/4 mark. Apparently the sensor is good.

Looks like I have to move on to something else. Relay circuit?

http://www.bba-reman.com/content.aspx?content=DTC_P0480_WITH_AC

Troubleshooting steps chart a little bit down the page....

Just thought I'd do a followup in case anyone else encounters this problem. After running thru all the troubleshooting procedures & talking with a mechanic friend, we decided the only possibility was a bad wire somewhere in the cooling fan circuit. I pulled the PCM (computer) which is located inside the air cleaner box. To get at it, I 1st had to remove the coolant reservoir & the support member. I removed the PCM & disconnected the plugs to check for any signs of corrosion or burned pins - all was well. But as I was putting things back together, I noticed a tear in the tape wrapped around the wiring harness. The tear was on the underside, at the point where the harness passes thru the air cleaner box. I peeled back the tape a bit & found a broken green wire. I pulled up the wiring diagram & sure enough, the green wire goes to the relay for cooling fan 1. I couldn't pull enough slack to reconnect the break, so I had to splice in a short piece of wire. There is a "foam protector" that is supposed to protect the wires at this "pass-thru" point, but it was out of position & appears that it's been that way since day one. I taped everything up really good, repositioned the foam & put it all back together. I cleared the code again, then fired up the van. I let it run for a bit & the fans kicked on when the temp gauge reached the 1/2 way point. I haven't driven it much since the repair but so far, the check engine light has remained off & no codes have reset. I think I got the bastard! :iceslolan

I hope this helps anyone else struggling with the same issue.

Woooo hooooooo!!!!!!!!!!!!

lesterl - I'm having the same issues you reported on my 2002 Venture that I just bought. I haven't checked the wires running to the PCM yet but I'd like to know how you hotwired the fans to test if they are working.

Could you reply back with directions on how you bypassed the relays. Do I have to disconnect the PCM before I bypass the fan relays to make sure I don't short something out in the PCM?

OP is the one who did that, but you could pull the relay and jump a wire between the two terminals that are the contact points to test the fans. Pull the relay and usually somewhere on there is a diagram of the internal electrical structure and you can see the coil and the contacts......