Cooling fan not coming on, but does with a/c
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Cooling fan not coming on, but does with a/c
New to this forum, but I've had my 96 SL1 for about 7 years, and know it very well. Was a long time user of saturnfans.com, but that site is apparently no more? Anyway, I have a problem that I can't figure out. The cooling fan comes on with the a/c, but it does not come on when the engine is getting hot without the a/c on. In the time I've owned the car, I've replaced the ECTS and its pigtail, and the cooling fan motor. The dash temp gauge is working normally. Sometimes when sitting in slow/stopped traffic for a while, it will start to overheat. If I notice it before steam starts coming out of the hood, I can turn on the a/c and the temp comes down immediately. The a/c, which I've rebuilt a couple times now, works great. Almost too cold.
Looking for any ideas or experiences. Thanks!
Looking for any ideas or experiences. Thanks!
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Joined: Jul 2005
Posts: 12,316
From: Slightly off center
A couple possibilities here: (sorry this is poorly worded but I have a migraine)
1) ECTS defective
Remove the squeeze connector of the pigtail and measure the resistance of the sensor for a cold engine and at operating temp.
while at the same time hooking up an OBDII scanner (not code reader) and tracking the real-time coolant temp sensor PID data from startup on......
If the resistance is infinite, the sensor has failed open circuit.
IF it is not open circuit, note the resistances and temp and post here.
2) Measurement current not getting to sensor
With the connector off, measure the DC voltage across the two sockets. With no load, one should be about 5 V.. One is +5, the other ground. Measure each separately vs chassis ground to be sure the ground connection is intact. Can also measure ohms betw each and ground, but I don't like doing that with the circuit energized if I don't have to. The meter impedance is high enough that it won't hurt anything. More of a best practice.
Oh -- the conductors at the connector can get flaky and sometimes you can see the V but b/c the meter has such a high resistance, no real current is flowing. When it is hooked up to the sensor, however, if it's a bad connection at the connector, it cannot carry enough current for the proper measurement to be made.
3)If you don't see +5V on one of the two wires, it's time to trace the wires to look for damage on the way back to the PCM. Hopefully, you find damage
4) If you don't find damage, then if you don't find voltage at the PCM pin for it, that indicts the driver in the PCM...
-----------------------------------
Genl questions
You said the temp gauge seems to work fine.
Where does it read at operating temp and where is the gauge reading when you start to see steam?
If the sensor was completely failed I'm not sure what the temp gauge would read.
Leave the connector off and take a look. Might take a few minutes -- built-in hysteresis and overdamping of the gauge.
How quickly will the car overheat if you start it in the driveway and just let it idle?
Does the temperature shoot up like a rocket or does it slowly climb like normal?
-------------
OTHER possibilities
include thermostat and water pump issues but let's rule out the easy stuff first.
Having a scanner reading real time data on the coolant temp will help you immensely as will your multimeter.
I believe you can do loan a tool for a scanner at autozone.
1) ECTS defective
Remove the squeeze connector of the pigtail and measure the resistance of the sensor for a cold engine and at operating temp.
while at the same time hooking up an OBDII scanner (not code reader) and tracking the real-time coolant temp sensor PID data from startup on......
If the resistance is infinite, the sensor has failed open circuit.
IF it is not open circuit, note the resistances and temp and post here.
2) Measurement current not getting to sensor
With the connector off, measure the DC voltage across the two sockets. With no load, one should be about 5 V.. One is +5, the other ground. Measure each separately vs chassis ground to be sure the ground connection is intact. Can also measure ohms betw each and ground, but I don't like doing that with the circuit energized if I don't have to. The meter impedance is high enough that it won't hurt anything. More of a best practice.
Oh -- the conductors at the connector can get flaky and sometimes you can see the V but b/c the meter has such a high resistance, no real current is flowing. When it is hooked up to the sensor, however, if it's a bad connection at the connector, it cannot carry enough current for the proper measurement to be made.
3)If you don't see +5V on one of the two wires, it's time to trace the wires to look for damage on the way back to the PCM. Hopefully, you find damage
4) If you don't find damage, then if you don't find voltage at the PCM pin for it, that indicts the driver in the PCM...
-----------------------------------
Genl questions
You said the temp gauge seems to work fine.
Where does it read at operating temp and where is the gauge reading when you start to see steam?
If the sensor was completely failed I'm not sure what the temp gauge would read.
Leave the connector off and take a look. Might take a few minutes -- built-in hysteresis and overdamping of the gauge.
How quickly will the car overheat if you start it in the driveway and just let it idle?
Does the temperature shoot up like a rocket or does it slowly climb like normal?
-------------
OTHER possibilities
include thermostat and water pump issues but let's rule out the easy stuff first.
Having a scanner reading real time data on the coolant temp will help you immensely as will your multimeter.
I believe you can do loan a tool for a scanner at autozone.
Last edited by derf; Jan 21, 2020 at 09:51 PM.
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