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Discussion Starter · #1 ·
2002 3.8 Usually never have the fan come on. Its cold in Oregon this year and the car never runs hot anyway--I rarely hear fan. Tonight I noticed the fan came on very loud when I started it up. About five miles down the road, the temperature guage went to zero. five more and the 'service engine soon' light came on. I checked and it hadnt lost its coolant. Fan stayed on the whole trip though and its never done that before. All other instruments work fine but temp.
 

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Pontiac Firebird 1994 3,4l L32
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Check the OBD scanner for errors (I won’t explain how this happens, the guys have already talked about this many times).
Do you hear a strong hum from the cooling fan?
How long ago was the coolant changed?
I take it there are no leaks from the cooling system?
 

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Discussion Starter · #3 ·
Has coolant, not sure how old. Looks red though. The fan makes a lot of noise---very loud roar. I have other birds with guages and light problems probably the control modules but this is just the temp guage and it happened the same time the fan decided to stay turned on fully. It starts to roar even at first startup after setting ijn the cold all night. Never did that before.
 

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Pontiac Firebird 1994 3,4l L32
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If I were you, I would change the coolant and flush the cooling system, especially when you don’t know about its origin and about the last replacement. Judging by the symptoms that you described, there may be a problem in the thermostat (especially since you say that no one has changed the antifreeze). As for the hum of the fan, you can connect it directly and check what is causing the noise.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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A dirty radiator or dirty coolant will not turn on the SES light. Yes, it's always a good idea to change fluids when maintenance is unknown, but that is not a primary cause of a code or the fan turning on when the coolant temp is below 226-degF. It's possibly a problem with the coolant temp sensor, or some other component that causes the PCM to default the fan(s) to "ON".

Let's focus on the problem he described. And yes, scanning the PCM for codes would probably point directly to the problem.
 
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Discussion Starter · #9 ·
The 'service engine' light came on at the same time the temp guage quit working and read zero. The fan now comes on when the engine is started cold and it never did that before.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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I understood that clearly from your first post.

A sensor likely failed and set a code, and the PCM responded by turning on the coolant fans to protect the engine from overheating. There are several diagnostic codes that cause the PCM to do that.

I THINK the 2002 3.8L V6 has a single coolant temp sensor under the throttle body. That sensor feeds the PCM, and the PCM passes the temperature data through to the dashboard instruments via the Class 2 data stream. Everything is pointing to the coolant temp sensor or the wiring. Maybe the harness connector clip was loose and the connector fell off.

But rather than guess as to the cause, pull the diagnostic code using an OBD-2 scanner. Always a lot less expensive than playing “parts replacement roulette”. :)
 

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Pontiac Firebird 1994 3,4l L32
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Marvin, buddy, don't be upset. Nothing is impossible. Everything can be repaired, the main thing would be desire and opportunities. The guys here will help you figure it out. And your Pontiac will delight you again.
 

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Discussion Starter · #13 ·
Thanks Injuneer, Thats a good description. Im going to buy a code reader. I guess coincidense but I started it up and it sounds like part of the valve train went bad. A loud wobbling rattle like everything is dry. No oil in water, no water in oil. Man this is a jinxed situation.
 
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