Re: P0481 on grand prix 2002. cooling fans work with a/c...
Sounds normal, the fans were made to run continuous w/ ac running, but on sensor when ac is off. if car isn't overheating, the fans are probably running from time to time ,but your just not catching them running
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Have the vehicle checked for DTC'S - diagnostic trouble code's if you haven't already . The vehicle has two cooling fans an three control relay's that are energized by the PCM - engine computer . Coolant temp sensor tell's the PCM engine temp.
Do you know what a wiring diagram is ? Free one's here http://www.bbbind.com/free-tsb Enter vehicle info. year make , model an engine . Under system click on engine ,then under subsystem click on cooling fans . Click the search button then the blue link. Watch this video. Relay Driven Dual Cooling Fan Diagnostics
Also ,what are you going by to say it's overheating ? Temp gauge in the instrument cluster ? GM had problems with Stepper motors inside the instrument cluster . 2003 - 2006 . Hooking up a scan tool that can view data would show what the coolant temp sensor is tell the PCM .
Using a infered temp
This would show the real temp of the engine.
DTC P0480 or P0481
Battery positive voltage is supplied to the cooling fan 1 relay from the COOL FAN #1 fuse. The powertrain control module (PCM) controls the cooling fan 1 relay by grounding the low speed cooling fan relay control circuit via an internal solid state device called a driver.
Battery positive voltage is supplied to the cooling fan 2 relay and the cooling fan 3 relay from the COOL FAN #2 fuse. The PCM controls the relays by grounding the high speed cooling fan relay control circuit.
When the PCM is commanding a relay on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a relay, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.
The PCM will monitor the control circuit for the following conditions:
• A short to ground
• A short to voltage
• An open circuit
• An open relay coil
• An internally shorted or excessively low resistance relay coil
When the PCM detects any of the above conditions, the DTC will set and the affected driver will be disabled.
I would say the instrument cluster is probably the problem . If the fans come on when A/C is turned on the system is working.
What year is the vehicle ? The cooling fan relays have nothing to do with the temp. gauge . GM had problems with the stepper motors inside the instrument cluster . Hooking up a professional scan tool to check what the PCM - engine computer is seeing from the engine temp sensor . You have duel cooling fans controlled by three relays . Checking to see what the actual engine temp. would be the first step , checking to see if the scan tool can control the cooling fans .
Look on youtube at videos on gm instrument cluster stepper motor problems
Learning how to test these systems an learning how they are suppose to work before replacing parts is what should be done , an if you don't know how you should take it to a qualified repair shop. The Temp sensor is an input to the PCM - engine computer .The PCM turns the fans on by energizing three relay's .Hooking up a factory scan tool that can view sensor data is how we do it at the dealer , Plus scan tool has bi-directional controls . I can energize the cooling fans with the scan tool ,check for DTC'S - diagnostic trouble code's .Turning on the A/C would cause the PCM to turn on fans on low speed . Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info year , make , model an engine size ,. Under system click on engine , under subsystem click on cooling fans . Click the search button then the blue link . Relay Driven Dual Cooling Fan Diagnostics
the temperature sending unit on a 97 grand prix 3800 gt(which is also the coolant temperature sensor) is not accurate. the sending unit part of this sensor only sends info to the guage on the dash. the coolant sensor part sends info to the computer of the car. it is located under thermostat and somewhat difficult to get at. i had put a brand new one in and my temperature on my dash is all over the place---even with good thermostat and properly bled system. when i hook up a scanner to my computer, the coolant sensor is sending the computer(ecu??) what seems to be the right temp. anywhere from 194 degrees to 217 when hot. the guage however on dash go from 160 to 260 in less than 2 minutes.
check to see if the electric fan is coming on when it should. Also check coolant level. Also, you may have the beginning of a plugged radiator If all else is OK flush radiator out.
there is no computer to turn the fan on. it works on a thermal switch. so you have a relay to the fan. when the temp sensor gets hot it connects the circuit to the relay and then the fan is on. vary simple. and it works when the car is still hot but the key has been turned off till the switch cools off or some have a timer so it does not run for ever. so good guess is the temp sensor for the fan could be bad if the fan is working.
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