my Cadillac's cooling fans do not come on at all i have checked the fuse, and the ac comp relay, my ac compressor also does not come on, but the interior fans work just no ac i did a code scan and got 1 code: p1660- cooling fan control circuit, i need to know how to test the cooling fan motor, the cooling fan relays, the relay and motor plug ins, and the coolant temperature sensor also where is the coolant temperature sensor located on my vehicle ?
Your ECT sensor is a pain to get to. I'd look at the ECT temp on a scanner to see if it's working instead of trying to access the ECT sensor itself.
You can test those fans like any other fans. Unplug the connector at the fan. Grab a couple of lengths of wire that are long enough to reach from the battery to the fans.
Jump battery positive to one terminal of the fan and battery ground to the other terminal.
Like this.
That will let you know if the fan motors work.
If they work then the only other things for now is to make sure that the AC compressor fuse is good. (It provides power to the control sides of the AC clutch relay as well as the control sides of the Cooling fans 1,2, and 3 relays).
Also make sure that the 50A Cooling Fans fuse is good. (It provides power to the load side of cooling fans relays 1 & 3).
If all that's good and you want to discuss how that "Triple Fan Relay" setup works to control the speeds of the fans and how to test that circuit let us know.
I checked all the plugs for the relays all the relays are good but I’m not getting any continuity on the the relay plug to the left closest to the battery not sure what the problem could be also found the temperature sensor I unplugged and the coolant temp said -40 and plugged it back in and it went back to a normal temp, could it still be bad ?, could the ac compressor not working have anything to do with it? Please get back to me when you have time
I also checked the motors and wired then direct with wires and clamps to a switch so I can still use the fans if the coolant gets to hot, but I’m eager to actually fix the problem the right way
Your test confirmed that the wiring between the ECT sensor and the computer is good
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On those old GMs I think the computer kicks on the fans to Low Speed around 225° and then to High Speed around 10° higher
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Did your ECT scanner reading show that the ECT sensor is seeing that?
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You never said if the car was actually overheating. Could you be dealing with a stuck open thermostat and the coolant never reaches the temp to kick on the fans?
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Anyway, the way this circuit works is the computer provides a Ground to the Control Side of each of those 3 relays to control the speed of the fans
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I lit up that wiring diagram in both the Low Speed and High Speed relay configurations.
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RED is Power from the 50A Cooling Fans Fuse to the Load Side of relays 1 & 3. (Relays socket pins 30)
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PINK is Power from the 10A AC Compressor Fuse to the Control Side of all 3 relays (Relay socket pins 85)
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GREEN is Ground. (notice Ground Point G107 in the lower right of the diagram. That's where the fans are Grounded on the LOAD SIDE of the circuit)
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Other than that Ground Point the other Greens are the computer providing Grounds to energize the individual relays at relay sockets 86
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I put a Purple Line inside the relays to show when the computer energizes the individual relays and closes the contact between relay sockets 30 & 87
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Let's say the ECT sensor is reading above 225° and the computer commands the fans to run on LOW SPEED
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The relay LOAD SIDE configuration looks like this.
(You should be able to click these images to enlarge them)
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Here Relay 1 is energized by the computer and Relays 2 & 3 aren't
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This creates a "Series Circuit" to the two fan motors. That just means that they have to share the 12 volts from the battery. Each gets around 6 volts and they run at LOW SPEED
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Let's say the ECT temp reaches around 235° and the computer commands the fans to run at HIGH SPEED
Here the computer energizes all 3 fan relays and instead of the fan motors being wired in Series, they're now wired in Parallel circuits so each fan motor gets 12 volts and run at HIGH SPEED
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The computer kept Relay 1 energized. It also energized Relay 2 and closed relay sockets 30 & 87 which gives the LH fan motor a direct path to ground at Ground Point G107
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Meanwhile, it energized Relay 3 which provides Power from the 50A fuse directly to the RH fan motor instead of Power going through the LH fan motor
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So how do you test the circuit? Grab a test light and a paper clip
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Disconnect the wiring connector from relay socket 1. Check for Power at the socket that corresponds to relay pin 30. If you have power there, use the paper clip to jump Relay 1 sockets 30 & 87
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The only way this test can bite you in the butt is if relay 2 is stuck in between pins 87 and 87A
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But here you can just unplug relay 2 , grab another paper clip and jump the #2 relay sockets 30 & 87A as you jump #1 relay sockets 30 & 87
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Helpful diagram
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Let us know what you find out. This test is mostly for the Load Side of the circuit
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If it checks out OK then it's time to check the Control Side of the circuit. (Computer provided Ground to relay sockets 86 and the 10 amp fuse power source to relay sockets 85)
Could the ac compressor not working affect the cooling fans ?, also only one plug in for the fans isn’t getting power, I just need to know how to fix that or if there is something else that controls the one relay plug also before it gets power to it
Just replace the fan control module and the temperature sensor. If you want, run 12 volts directly from the battery to the fans and see if they work The temperature sensor is usually located on the intake manifold, in a water passage near the thermostat.
Where is the fan control module
No. The AC compressor not working won't affect the cooling fans operation
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1st Question: In this image of your cooling fans, is the one that's not getting power labeled #1 RH cooling fan (the fan on the passenger side)?
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2nd Question: Are you able to locate the 3 relays in the picture and if so, are you able to jump pins 30 and 87 of the Engine Cooling Fan Relay #1 socket or do you need help on how to do that?
The answer to your first question is no, it is the engine cooling fan relay 3 in the diagram that wasn’t getting continuity and I do need help on how to jump pins 30 and 87 of the engine cooling fan relay #1 socket
Let me make sure I'm up on current events
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1) You can provide power and ground to the fans directly and they BOTH work
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2) You've checked both the 50A Cooling Fans fuse and the 10A A/C Compressor fuse and they're both good
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If we play the odds we'd have to assume that it's either a bad ECT sensor or a bad relay
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3) In one of my replies I brought up hooking a (cheap) scanner up and looking at what the ECT sensor is showing when the engine warms up. You should do that first to make sure the problem isn't just a bad ECT sensor
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If the ECT sensor temp looks good then that leaves either relays or wiring
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Since you're dealing with a 25 year old car, I suggested jumping the #1 fan relay sockets 30 & 87. That's because I wanted to know if this was a wiring issue on the Load Side of the fan circuit
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But to access those relays and their sockets you probably have to lay on your back and get under the radiator and working in that position on anything isn't fun so why not test those 3 relays first before testing their sockets? You still have to go down there to pull them out but you can do the tests "above ground"
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I'm going to assume that GM used the same 5 pin relays on those fans as they did on the fuel pump
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The pin assignments look like this:
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There's plenty of youtubes on how to energize and test these relays
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I'll give you the short version
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At rest (no Power, or in your case no Ground, to the control side Pins 85 & 86) there should be continuity between relay pins 30 & 87a
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If you put Power to relay pin 85 and Ground to relay pin 86 you should have continuity between relay pins 30 & 87 (You can use your car battery and jumper wires to do this)
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Check all 3 relays the same way
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Let us know if all 3 relays test OK and we can move on to testing their sockets
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((also let me know if I'm wrong about my assumption of which relays GM used for the fans. If I am, take a picture of your relay showing the pins and include any markings on the relay))