Radiator fan on 91 cav
August 25th, 2011, 10:52 AM
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Radiator fan on 91 cav
Radiator fan doesn't work., works when jumped. Changed thermostat, coolant temp fan switch, and relay on the firewall. what am I missing? (The car does overheat.) help!
August 25th, 2011, 11:45 AM
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Bojac,
Did you try replacing the fan motor? It's about a $120 part from the dealer and $70 from gmpartsgiant.com, from what I recall. The installation process isn't too difficult either
Did you try replacing the fan motor? It's about a $120 part from the dealer and $70 from gmpartsgiant.com, from what I recall. The installation process isn't too difficult either
August 25th, 2011, 11:46 AM
#3
Welcome to the forum, bojac. In order for the cooling fan to run, the ECM has to be able to determine the temperature from the ECT sensor and then command the fan on with the relay. So, you have the ECM, some wiring, a sensor, and a relay to check. Does the fan come on with A/C on? How about, if you unplug the electrical connector from the ECT sensor and short it across (connector, not the sensor)? If the fan then comes on, the ECM is able to command the fan on and thus you'll want to concentrate on the ECT sensor and wiring. If not, you'll want to concentrate on the relay and wiring. In any case, often the wiring degrades over time and develop breaks or spots with high resistance internally.
In order for the cooling fan to run, the ECM has to be able to determine the temperature from the ECT sensor and then command the fan on with the relay. So, you have the ECM, some wiring, a sensor, and a relay to check. Does the fan come on with A/C on? How about, if you unplug the electrical connector from the ECT sensor and short it across (connector, not the sensor)? If the fan then comes on, the ECM is able to command the fan on and thus you'll want to concentrate on the ECT sensor and wiring. If not, you'll want to concentrate on the relay and wiring. In any case, often the wiring degrades over time and develop breaks or spots with high resistance internally.
August 25th, 2011, 7:30 PM
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I replaced the ECT again today. ( The one I replaced yesterday tested bad with sensor tester & heat) Then the car wouldn't start. So I disconnected neg bat cable for a while, hooked it up and car started. fan still doesn't work. Fan by its self tests okay. new ECT,( now maybe burned out), new relay. Air conditioner doesn't work, blows the fuse. Radiator fan and AC on same circuit? Since I had to reset ECM, could it be bad? I don't even want to think short. Me and Electrical don't get along. Engine light never comes on when running.
Last edited by bojac; August 25th, 2011 at 7:43 PM.
August 25th, 2011, 7:39 PM
#5
Did you unplug the electrical connector from the ECT sensor and short it across (connector, not the sensor) with key on and then observe the fan? What do you mean by "Fan by its self tests okay," in specific detail? You posted something about "works when jumped" but where was the jumper? And, by "blows the fuse," which fuse?
August 26th, 2011, 9:41 AM
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Yes, I jumped ECT connector with switch on, no fan. What I meant by jumping fan motor was by unplugging at the motor and running + and - jumper wires straight to battery. Then fan works. (fan by its self works ok) AC blows htr/ac 25 amp horseshoe fuse.
Last edited by bojac; August 26th, 2011 at 9:45 AM.
August 26th, 2011, 11:59 AM
#7
I had to sit down and give some thought to this but wiring on a vehicle this old is always suspect and thus do take the following with a grain of salt.
The ECM supplies the ECT sensor a reference voltage on one wire and ground potential on the other. Check the voltage level and continuity to the known good ground at the ECT electrical connector with key on. If they don't check out, the ECM has no way of sensing the temperature.
The 25A HTR-A/C fuse supplies the ignition voltage (hot with key on) to the coil in the cooling fan relay. The ECM then grounds the other side of the coil to energize the relay. The coil terminals are numbered 85 and 86 on the relay. Pull the relay and then check the voltage level and continuity to the known good ground at the said terminal sockets when the fan should be on e.g., with the ECT connector shorted across and key on. If they don't check out, the ECM has no way of commanding the fan on.
The fusible link L supplies battery voltage (hot always) to the cooling fan relay. The terminals are numbered 30 and 87 on the relay, one gets the voltage and the other connects to the cooling fan. With the relay pulled, check the voltage level at one of the two terminal sockets (may be either 30 or 87). Check the continuity between the other terminal socket and the supply wire at the cooling fan connector (colored something other than BLK). If they don't check out, the fan can never be powered.
The BLK wire at the cooling fan connector should be connected to ground to complete the circuit. Check the continuity to the known good ground.
The ECM supplies the ECT sensor a reference voltage on one wire and ground potential on the other. Check the voltage level and continuity to the known good ground at the ECT electrical connector with key on. If they don't check out, the ECM has no way of sensing the temperature.
The 25A HTR-A/C fuse supplies the ignition voltage (hot with key on) to the coil in the cooling fan relay. The ECM then grounds the other side of the coil to energize the relay. The coil terminals are numbered 85 and 86 on the relay. Pull the relay and then check the voltage level and continuity to the known good ground at the said terminal sockets when the fan should be on e.g., with the ECT connector shorted across and key on. If they don't check out, the ECM has no way of commanding the fan on.
The fusible link L supplies battery voltage (hot always) to the cooling fan relay. The terminals are numbered 30 and 87 on the relay, one gets the voltage and the other connects to the cooling fan. With the relay pulled, check the voltage level at one of the two terminal sockets (may be either 30 or 87). Check the continuity between the other terminal socket and the supply wire at the cooling fan connector (colored something other than BLK). If they don't check out, the fan can never be powered.
The BLK wire at the cooling fan connector should be connected to ground to complete the circuit. Check the continuity to the known good ground.
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August 26th, 2011, 1:49 PM
#8
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Do the same with key on, and jumper the temp switch connector, check relay coil for 12 volts, if so, and, you have 12 volts to the normally open contacts it is the relay. I am not sure about the fan circuit, but fuel pump has 12 volts at the contacts with key on. I would think the same with fan circuit. I'll look at my Haynes manual for my lumina, and post back.
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