At what temperature does the engine ECM bring the cooling fans on?

LARANDY1

MEMBER
2002 BUICK CENTURY
3.1L
V6
2WD
AUTOMATIC
250,000 MILES

Engine will overheat and go into red on temperature gauge on dash. Have hooked up to the diagnostic connector and used software to check engine temperature which was 224 degrees. Has no DTC 's what temperature does the engine ECM bring the cooling fans on. It has two fans which can be operated by pulling the fan relay and jumping the contacts at the relay panel. Has no ground from ECM to activate relay.

4 Replies

STEVE W.

MECHANIC
13,577 POSTS

224° shouldn't be in the red on the gauge as that is the point where the ECM commands the fans on at low speed. High speed isn't commanded on until 230°. It may be that the temperature sensor has skewed and now is reporting wrong. The temperature sender is next to the thermostat housing. I would start with replacing it and see if it still reports the same. The sensor data is used for both the gauge and the fans. That is what doesn't fit, if the dash reads in the red the coolant temperature should be about 240 degrees.
How fast does this happen from a cold start?

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Thursday, May 16th, 2024 AT 7:49 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

I'm looking at the wiring schematic and it appears the ECM doesn't control the ground path for the relays. There are three cooling fan relays. They receive a ground at the front of the engine.

I attached a pic below of the wiring schematic. Note the ground. It's not from the ECM. If you have no continuity to ground, I suggest tracing the wire to see if there is a connection issue. Also, I noted a there is also a splice. That could be an issue as well.

Let me know what you find.

Joe

See pics below.

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Thursday, May 16th, 2024 AT 7:55 PM

LARANDY1

MEMBER
2 POSTS

Found the problem. Checked the coolant protection in radiator and it was +5 degrees. Unhook the water pump hose and drain out. Add 1/2 gallon of concentrate coolant. Start engine and monitor coolant temperature to 224 degrees. Both fans at low speed. Test drive for 10 miles and monitor cooling temperature. 208 degrees. No codes and no leaks. Verified fan cooling electrical system and is ok. That was the only thing that wouldn’t work.
I work on heavy trucks for over 40 years and didn’t know the conditions to bring the fans on. If it was a KW I would tell you about it. Thanks for all the good help!

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Friday, May 17th, 2024 AT 5:35 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Thanks for the update. I'm glad you found the issue. As far as working on KW, that is beyond me. LOL

Take care and feel free to come back anytime in the future.

Joe

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Friday, May 17th, 2024 AT 8:12 PM