Fan stopped working
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
Likes: 1
From: Oklahoma City OK
St. Jude '10
Fan stopped working
When I was installing my headers I broke a sensor on the pass side of the block just between and below 3rd and 4th cylinders. I bought the "coolant temp sensor" only to find out it wouldn't plug in so then I had to buy the "coolant temp switch". It fit perfect and my temp gauge is working again. The fan wasn't coming on so I took it for a run and thought all was well but When I got back and let the car idle still no fan even up to 250 degrees. Anyone know what would cause the fan not come on? It works fine in AC mode so it's not the fan motors.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
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From: Palm Beach
The sensor you describe is actually in the head between the #6 and #8 cylinders. It is the sender for the analog temp gage. It has nothing to do with the fan.
The fan is controlled by the PCM using the temp provided by the Coolant Temp Sensor (CTS) in the water pump. With AC off the fan should come on in the vicinity of 228 as registered on the digital readout..
The fan is controlled by the PCM using the temp provided by the Coolant Temp Sensor (CTS) in the water pump. With AC off the fan should come on in the vicinity of 228 as registered on the digital readout..
Last edited by MK 82; Nov 22, 2009 at 03:43 PM.
Le Mans Master
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From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
my fan relay quit and I replaced it, don't know that the fan has another source to turn it on when the A/C is on, but I would guess that the A/C switch has an input to the computer to tell the computer to cycle the IAC and turn on the fan.
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
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From: Oklahoma City OK
St. Jude '10
I didn't check the digital, but I will. Doesn't this information come from the same source? I have the FSM's and I didn't even think to look in them for a trouble shooter section. But, there should be a schematic, I'm just not sure if I'm smart enough to figure it out.
Le Mans Master
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From: Orlando FL
As MK 82 pointed out the sensor on the right side of the engine is for the analog temp gauge. The digital temperature is driven by the sensor in the front of the water pump. This same input is fed to the ECM for engine operation. See If that sensor is broken or disconnected. But the digital temperature readout will tell you if the sensor is working.
In addition if the sensor in the pump is not working, the engine will run really bad and will be to rich. Having said that you have not indicated a engine running problem. So my thinking might indicate a possible problem with the ECM, or wiring/connections perhaps.
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
Likes: 1
From: Oklahoma City OK
St. Jude '10
No it doesn’t.
As MK 82 pointed out the sensor on the right side of the engine is for the analog temp gauge. The digital temperature is driven by the sensor in the front of the water pump. This same input is fed to the ECM for engine operation. See If that sensor is broken or disconnected. But the digital temperature readout will tell you if the sensor is working.
In addition if the sensor in the pump is not working, the engine will run really bad and will be to rich. Having said that you have not indicated a engine running problem. So my thinking might indicate a possible problem with the ECM, or wiring/connections perhaps.
As MK 82 pointed out the sensor on the right side of the engine is for the analog temp gauge. The digital temperature is driven by the sensor in the front of the water pump. This same input is fed to the ECM for engine operation. See If that sensor is broken or disconnected. But the digital temperature readout will tell you if the sensor is working.
In addition if the sensor in the pump is not working, the engine will run really bad and will be to rich. Having said that you have not indicated a engine running problem. So my thinking might indicate a possible problem with the ECM, or wiring/connections perhaps.
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Le Mans Master
Joined: Jan 2006
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From: Orlando FL
Just other thoughts.
You said the engine got to 250* (analog ?). The secondary fan (right side) should have come on at 239*. Sounds like if what you say that no fans are coming on. Both fans are controlled by the ECM and use the sensor in the pump as a reference. But the primary fan comes on with the A/C which is also controlled by the ECM via data from the A/C controller head. That is a strange symptom, hope it is not your ECM.
You also said the fans worked normal before doing the mod. Check around in the areas you might have been to see if there is anything you could have disturbed.
Also get a scanner to check your O2 and your BLM numbers. This will conform your belief on needing an tune and as to what may be going on.
You said the engine got to 250* (analog ?). The secondary fan (right side) should have come on at 239*. Sounds like if what you say that no fans are coming on. Both fans are controlled by the ECM and use the sensor in the pump as a reference. But the primary fan comes on with the A/C which is also controlled by the ECM via data from the A/C controller head. That is a strange symptom, hope it is not your ECM.
You also said the fans worked normal before doing the mod. Check around in the areas you might have been to see if there is anything you could have disturbed.
Also get a scanner to check your O2 and your BLM numbers. This will conform your belief on needing an tune and as to what may be going on.
Thread Starter
Melting Slicks
Joined: Feb 2009
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From: Oklahoma City OK
St. Jude '10
OK, The digital temp is working but is not in sync with the analog gauge. The analog got right up to 250-260 range and the digital was just getting to 225. When the digital went from 227 to 229 the fan kicked on like it was suppose to. So, how do I know which one is wrong. The switch (analog) sensor is new. The other sensor is only $10 so it won't hurt to change it but still it makes me wonder why it would have gone out. I try not to believe in coincidence to much. Would air in the system cause a problem with one of them? When I replace the switch I lost a bit of coolant but I would think the air would cycle through until it was released.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
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From: Palm Beach
How can you say the analog is wrong without verification. The fact that the fan comes on in the proper digital range does not mean it is accurate. The ECM is merely going by what the sensor is telling it, right or wrong.
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
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From: Oklahoma City OK
St. Jude '10
Well when I drove the car after the switch was installed the temp leveled off at around 180 - 190 or just before the middle hash mark on the analog gauge. So unless someone has changed tstat you could assume the analog was somewhat accurate at that point.
Le Mans Master
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From: One day you're a Comet...the next day you're dust... Arkansas
If the fan came on at the analog gauge reading of 260* and it was correct, now wouldn't that be peachy! The analog gauges on these cars are notoriously inaccurate.
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
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From: Oklahoma City OK
St. Jude '10
Either way it's a bit of a mystery, I'll get the other sensor changed and let you all know what it does.
BTW, thanks for the help. Right or wrong discussion is what helps us.
Le Mans Master
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From: Orlando FL
Boys boys.
All MK 82 is saying is that the ECM is tracking the sensor as far as the resistance goes. All the ECM knows is that at 228* it turns the fan on, and adjusts engine operation for that given resistance that it thinks the engine temperature it is at.
However if the sensors resistance for a given temperature is wrong and does not track the temp vs. resistance chart in the FSM than it is out of calibration. You would have to check the sensor using an ohm meter, for a known temperature and comparing it to the chart.
All the ECM knows is what the resistance is that it is looking at. It does not know that it is correct for that temperature.
Example; put in a fixed resistor in place of the sensor to simulate 200*. The ECM would always think the engine is 200* regardless of the actual engine temperature. You would always see 200 in the digital display.
All MK 82 is saying is that the ECM is tracking the sensor as far as the resistance goes. All the ECM knows is that at 228* it turns the fan on, and adjusts engine operation for that given resistance that it thinks the engine temperature it is at.
However if the sensors resistance for a given temperature is wrong and does not track the temp vs. resistance chart in the FSM than it is out of calibration. You would have to check the sensor using an ohm meter, for a known temperature and comparing it to the chart.
All the ECM knows is what the resistance is that it is looking at. It does not know that it is correct for that temperature.
Example; put in a fixed resistor in place of the sensor to simulate 200*. The ECM would always think the engine is 200* regardless of the actual engine temperature. You would always see 200 in the digital display.
Le Mans Master
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From: One day you're a Comet...the next day you're dust... Arkansas
Guys, read my posts, I didn't say the sensor was wrong I said the analog gauge is wrong. I have no way of knowing why, but a good indicator is that two different sensors apparently showed about the same reading on the analog gauge and yet the fan came on when the digital readout was at the proper temperature. A temp of 255-260 is pretty warm and yet no evidence of over heating was posted. If the car is showing no other signs of running hot and the fans go on and off when they should by the digital gauge, I think I would just ignore the analog gauge or try to determine why it is reading so high.
Last edited by BADDUCK; Nov 24, 2009 at 08:42 AM.
Thread Starter
Melting Slicks
Joined: Feb 2009
Posts: 2,072
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From: Oklahoma City OK
St. Jude '10
Guys, read my posts, I didn't say the sensor was wrong I said the analog gauge is wrong. I have no way of knowing why, but a good indicator is that two different sensors apparently showed about the same reading on the analog gauge and yet the fan came on when the digital readout was at the proper temperature. A temp of 255-260 is pretty warm and yet no evidence of over heating was posted. If the car is showing no other signs of running hot and the fans go on and off when they should by the digital gauge, I think I would just ignore the analog gauge or try to determine why it is reading so high.