Cooling Fan Problem
Thread Starter
6th Gear
Joined: Jun 2010
Posts: 6
Likes: 0
Cooling Fan Problem
Hello All, I'm new to the Forum and need help on a cooling fan problem. I purchased a 1990 coupe (31,500 miles) and found the temp gauge would climb into the shaded area while not moving. Neither the primary or secondary fans come on. So far I have checked and verified the following: 1. I checked all fuses and found no problem. 2. I jumped the A and B ports of the ALCL and both fans kick on. I believe this means both the fans and the relays are good. 3. If the AC is engaged the fans come on. Also found if the AC kicks out the fans also quit. 4. I did not find any flash codes other than 12 until I disconnected the coolant temp sensor in the intake which gave a code 15. 5. The cooling fan temp switch in the pass side head has a single wire Spade connector. Grounding this wire does not start the fans. All replacement temp switches I researched have a button type connector. I suspect this is the original switch. Perhaps the temp switch wire is open between the switch and the ecm?? Any suggestions?? Thanks Bob
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
Disconnect the electrical connector at the ECT (engine coolant Temperature sensor).
That's the plug with the Yellow and Black wire that you disconnected to get the error code 15.
With jumper clips or a piece of wire, short the Yellow wire to the Black wire. This should simulate the engine temp. is over 266 degress F. Start the engine. The ECM should turn the fans on.
If the fans work, that would indicate the ECT is bad. If you had a scan tool you could read what the ECM believes the engine temperature is.
The item you mentioned screwed into the passengerside head is the sender for the dash cluster temperature gauge.
That's the plug with the Yellow and Black wire that you disconnected to get the error code 15.
With jumper clips or a piece of wire, short the Yellow wire to the Black wire. This should simulate the engine temp. is over 266 degress F. Start the engine. The ECM should turn the fans on.
If the fans work, that would indicate the ECT is bad. If you had a scan tool you could read what the ECM believes the engine temperature is.
The item you mentioned screwed into the passengerside head is the sender for the dash cluster temperature gauge.
Last edited by Hooked on Vettes; Jun 27, 2010 at 08:20 AM.
Thread Starter
6th Gear
Joined: Jun 2010
Posts: 6
Likes: 0
Thank you for your recommendation. I jumped the yellow and black wire and the fans came on when I started the engine. I'll change out the ECT sensor and see how the temps are with the fans operating. What are your thoughts on the aftermarket low temp switch kit that kicks the fans on around 200 degrees?
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Thank you for your recommendation. I jumped the yellow and black wire and the fans came on when I started the engine. I'll change out the ECT sensor and see how the temps are with the fans operating. What are your thoughts on the aftermarket low temp switch kit that kicks the fans on around 200 degrees?
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The car is new to you and is low mileage. Fix the problem and drive it.
The radiator and fan layout was redesigned for the 90 Model.
Usually the guys with the 85-89 engines complain about the
high engine temps.
1) Each fan has a relay. You can use a manual switch and ground the Light Blue/Black wire at each fan relay socket and manually control each fan. Kits are sold to do this or go to Radio Shack and purchase the parts.
2) You can purchase a fan switch that screws into the Drive Side head that will ground the fan relays to turn the fans on at a lower temperature. Problem is getting the pipe plug out of the head to install the new fan switch.
3) You can have your ECM calibration Eprom reprogrammed for lower fan turn on. Paying to have it done would be over $100.00.
Lay on your back in front of the vehicle and look for any accumulated road trash that blocks the radiator air flow.
The radiator and fan layout was redesigned for the 90 Model.
Usually the guys with the 85-89 engines complain about the
high engine temps.
1) Each fan has a relay. You can use a manual switch and ground the Light Blue/Black wire at each fan relay socket and manually control each fan. Kits are sold to do this or go to Radio Shack and purchase the parts.
2) You can purchase a fan switch that screws into the Drive Side head that will ground the fan relays to turn the fans on at a lower temperature. Problem is getting the pipe plug out of the head to install the new fan switch.
3) You can have your ECM calibration Eprom reprogrammed for lower fan turn on. Paying to have it done would be over $100.00.
Lay on your back in front of the vehicle and look for any accumulated road trash that blocks the radiator air flow.
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
I use a F-body thermal sensor to turn my fans on now instead of through the ecm. Mine does the same as yours pretty much the temp gauge shows around 240'ish before the fans come on, but my thermal sensor is for 228on-205off. Probably just your gauge is a bit off like mine, my gauge almost redlines before the fans come on but it never smells hot.
Pro
Joined: May 2010
Posts: 679
Likes: 18
From: Vernon Hills Ill
I use a F-body thermal sensor to turn my fans on now instead of through the ecm. Mine does the same as yours pretty much the temp gauge shows around 240'ish before the fans come on, but my thermal sensor is for 228on-205off. Probably just your gauge is a bit off like mine, my gauge almost redlines before the fans come on but it never smells hot.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Just scan it so that you can see the Engine Coolant Temp Sensor. Non a/c specs for the '90 are 226 primary; 228 secondary. You've allready verified that the ECM can drive the Fans and that the Relays are good. What you want to know is if they're being grounded at spec temp. Doing anything else is a waste of time and money - you don't even know if it's broken.
Thread Starter
6th Gear
Joined: Jun 2010
Posts: 6
Likes: 0
I replaced the ECT sensor, started the engine and idled until temp gauge hit the caution shaded area prior to the 260 mark. Fans did not kick on. I heated the old sensor with a lighter and it had continunity. Engine cooled a little I removed the radiator cap. Inserted a thermometer and started the engine again. The temp gauge hit the shaded area prior to 260 but the thermometer read 200. I don't have a scan tool to see what the ecm temp is reading. I'm treading cautiously until I get grasp on the true temps. Thanks to all.
Thread Starter
6th Gear
Joined: Jun 2010
Posts: 6
Likes: 0
My temp gauge redlines at 260 degrees. It has a "Warning" shaded area on the gauge just prior to the 260degree mark. When the engine is running the temp gauge will reach this warning area and the cooling fans have not come on. I replaced the ECT (Engine Coolant Temp) sensor and the fans still haven't come on. I have already verified the fans and relays are good. When I jumped the pigtail to the ECT the fans came on. What I need is to verify the true engine coolant temp which I do not have the equipment to do at this time. I am not sure of the temp gauge accuracy but I'm not willing to risk running the engine once the gauge has redlined. Perhaps you missed my earlier comments about the inop fans as the original problem.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The service manual does not give the resistance of the sensor when the temperature is above 210 F. You already determined when the resistance is zero the fans come on. So the only conclusion is the engine temperature is not hot enough for the ECM to enable the fans.
210 F = 185 ohms
160 F = 450 ohms
100 F =1.8k ohms
70 F = 3.4K ohms
40 F = 7.5K ohms
20 F =13.5K ohms
Last edited by Hooked on Vettes; Jun 27, 2010 at 03:55 PM.
Thread Starter
6th Gear
Joined: Jun 2010
Posts: 6
Likes: 0
Final Update. I connected a secondary temp gauge along with the original gauge. I installed a thermometer where the radiator cap should be and idled the engine. The original temp gauge passed the 260 degree mark, the secondary temp gauge read about 200 and the thermometer hit 215 when the primary fan kicked in. Conclusion: The coolong system worked as it should. The factory temp gauge was no where near being accurate. Thanks to all for their input and ideas.
