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Old 09-01-2012, 11:35 PM   #1
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Default Rad Fans Not Coming on Engine over-heats

Rad Fans Not Coming on Engine over-heats But when I turn on the AC the fans kick-in and is all ok. At this point I have to keep the AC on to keep the engine cool I read the in other forums that the PCM may be bad or the coolant temp sensor. If I remove the temp sensor plug and short the 2-wires and if the fans start running is this a good test. I do not want to buy a PCM before I check the cheaper fixes 1st.
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Old 09-02-2012, 04:53 AM   #2
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It really helps if we know what you are driving. I would replace the coolant temp sensor before getting a new pcm. I don't think shorting the sensor will work. It'* not like an on/off switch for the fan. It tells the PCM what the coolant temp is, and the PCM turns the fans on.
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Old 09-02-2012, 05:21 AM   #3
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You could DISCONNECT the coolant temp sensor as a TEST. The fans should automatically turn on. This is a safety feature built into the PCM should it detect an open condition with the temp sensor.

Roy is correct though, we need to know what kind of car you have.
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Old 09-02-2012, 10:18 AM   #4
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Originally Posted by 2kg4u View Post
It really helps if we know what you are driving. I would replace the coolant temp sensor before getting a new pcm. I don't think shorting the sensor will work. It'* not like an on/off switch for the fan. It tells the PCM what the coolant temp is, and the PCM turns the fans on.
Sorry I'* a 2005 Chevy Venture. I did remove the plug to the temp sensor and the fans did come on, on high. Interesting I also had a 1999 Olds Intrigue and in it'* 8th year I was having the same problems with the fans. GM must be having the same problem on other models.

At this point I have to assume all is ok with the fans and other electrical connections. Can I also assume it may be the sensor or the pcm. If I was a betting man I would say it'* the pcm based on the fact I did replace the temp sensor on the olds and that did not solve the problem.
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Old 09-02-2012, 11:24 AM   #5
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It would appear that the system is working fine. Now, my question is, how hot is the temp gauge showing?
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Old 09-02-2012, 01:01 PM   #6
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It would appear that the system is working fine. Now, my question is, how hot is the temp gauge showing?
When the ac is running the temp gauge is 1/3 from Zero, with the AC off the temp gauge will read almost to the red zone in stop and go traffic and you can start smelling fumes from coming from the engine (burnt oil residue) At this point I did checked under the hood and no fans were running.

At this point I will run the van with the temp sensor unplugged and I also unplugged on of the fans to keep the drain on the battery and the wear on the fan ( at least on one of the fans)

As I stated had the same problem the way I solved that problem was GM had a $1,000 incentive if you traded a junker car even-though it was in great shape less the over-heating)
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Old 09-02-2012, 01:22 PM   #7
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Now im thinking your thermostat is sticking closed.
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Old 09-02-2012, 03:39 PM   #8
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Interesting thing I did unplug the temp sensor wire as stated and now the temp gauge is not working. I gues the temp gauge uses the same temp sensor. I guess this is what happens when you tinker with stuff. At least I know the engine is not overheating. I also have a temp gauge I can install just to keep my eye on the system.

I would have changed the stat But what was GM thinking. How does one get to it. I am feeling for those poor car techs.
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Old 09-02-2012, 04:14 PM   #9
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I really hope your not running around with that sensor disconnected. I offered that as a test only. Just change the thermostat.
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Old 09-02-2012, 05:04 PM   #10
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I really hope your not running around with that sensor disconnected. I offered that as a test only. Just change the thermostat.
Why do you think its the stat If the stat was closed then the engine will over-heat even with the ac on. I just bought this van so I have no idea if the stat was ever changed. My guess is due to its location I bet it was never changed.
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