Question about 2000 Oldsmobile Alero

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Cooling fans will not run

2002 olds. alero engine temp. does the pcm control the cooling fans?

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  • Anonymous Mar 18, 2014

    engine coolant temp gauge inoperative

  • Anonymous Mar 28, 2014

    pcm wiring diagram

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Yes, but it gets it's signsl from the temp sensor for the emissions system, not the one from the temp guage sensor. It could also be a fuse or relay.

Posted on Dec 27, 2008

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I have a 2000 Oldsmobile alero, it’s has new head gaskets, intake gaskets, new thermostat and coolant temp sensor but my coolant fans won’t turn on, if I turn the ac on they still don’t turn on, but if I...


What does scan data show ? Is the PCM - engine computer seeing coolant temp sensor input data ? Can the fans be truned on bi-directionally ? Do you know what that is ? Factory tech 2 scan tool can do that .
Your vehicle has two cooling fans and three relay's that the PCM energizes to control fan speed . Did you take your vehicle to a qualified repair shop ?
Relay Driven Dual Cooling Fan Diagnostics

Free wiring diagrams here http://www.bbbind.com/free-tsb

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2005 Saturn relay is overheating the fans do not turn on. I checked fuses relays and when I turn on the air conditioner they run on low speed


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
infered temp.-iyt4esw4bjav4jkg3wd2waqn-3-0.jpeg 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.

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Can someone help me on locating my c?oling fan switch on my 2003 ford escape.


Cooling fan switch ? The cooling fans on your vehicle are computer controlled . Relay's energized by PCM - engine computer . Coolant temp sensor is a input to the PCM ,when the temp. reaches 212 degress the PCM will energize the low speed fan relay ,if temp reaches 250 degress the PCM will energize the high speed cooling fan relay . Hooking up a scan tool an checking coolant temp. sensor data to the PCM and checking control from the PCM ( energizings relay's ) Is how to diagnose this . Not replacing parts and hope you fix the problem . Your best bet take it to a qualified repair shop.

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1 Answer

Does my 2002 Cadillac Seville SLS have a cooling fan switch, and, if so, where is it located?


Cooling fan switch ?????? Has a engine coolant temp. sensor , That inputs info to the PCM/ECM - engine computer ! The PCM / ECM interpits the voltage signal from software programmed into it as to what temp . of the coolant is . When the engine coolant temp. reaches
The PCM commands the low-speed fans ON under the following conditions:
• The engine coolant temperature exceeds approximately 106°C (223°F).
• The transmission fluid temperature exceeds 150°C (302°F).
• The A/C pressure reaches 199 psi (1372 kPa).
The cooling fans will switch from low to OFF when the coolant temperature drops below 102°C (216°F).
The PCM commands the high-speed fans ON under the following conditions:
• The engine coolant temperature reaches 112°C (234°F).
• The transmission fluid temperature is more than 151°C (304°F).
• The A/C pressure reaches 260 psi (1792 kPa).
• Certain DTCs are set.
The cooling fans will switch from high to low, except when DTCs are set, when the coolant temperature drops below 106°C (223°F).

The PCM turns on the cooling fans by energizing three different relay's .
Watch this video
Relay Driven Dual Cooling Fan Diagnostics

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1 Answer

2001 montana cooling fans not coming on


A pontiac montana ? There are three relay's that control your cooling fans ! unplug what sensor ? The engine coolant temp. sensor is an input to the PCM - engine computer . When temp. reaches 213 degrees the PCM energizes the relays , depending on low or high speed . Using a scan tool to see if the PCM will turn on the fans an checking engine coolant temp.data is the right way to diagnose this . Relay Driven Dual Cooling Fan Diagnostics

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1 Answer

I have a 2002 Lincoln town car and I just put a brand new fan in and its not coming on my car runs hot when I have it in park with the ac on


Did you check the fan relays ? There are two, cooling low relay an cooling fan high relay . The relays are turned on by the vehicles PCM - engine computer , when an input from the coolant temp. sensor indicates a certain temperature ! When you turn on your A/C the cooling fan should turn on an stay on .
Relay Box
Left center of engine compartment
Cooling Fan High Relay
In relay box
Cooling Fan Low Relay
In relay box
Do you know how to test a computer controlled relay ? Go to you tube an search relay testing . Does the temp. gauge work correctly ? I know you probably don't have a factory scan tool , but this is the where I would start , checking temp. sensor input to the PCM . An with a factory scan tool I can do bidirectional testing , see if I could turn the fans on will scan tool .

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1987 olds cutlass ciera 3.8 cooling fan runs when engine is cold; changed cooling fan switch and temp sensor, fan relay times out OK.


the coolant fan does not only cool down engine temp. it also run if pcm detect a problem .or ac request. see pcm data to find out code or data out of range

Aug 21, 2013 | 1987 Oldsmobile Ciera

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I have a 1999 Alero 3.4 V6 the cooling fans won't run. I checked the fans they both work if I unplug the harness for the temp sensor,the relays and fuses are fine,I replaced the coolant temp sensor and...


CHECK MODE RELAY IF BOTH RELAYS GOOD YOU CAN CHECK RELAY BY REMOVING IT FROM FUSE BOX HOOK RELAY TERMINAL 85 TO BATTERY POSITIVE AND GROUND TERMINAL 86 IF CLICKS RELAY GOOD. IF RELAY GETTING POWER GOOD AND THE 30 AMP COOLING FAN FUSE OKAY.EITHER THERE IS A SHORT IN COOLING FAN WIRING OR THE PCM HAS FAILED.THE PCM HAS LOST OR COMMAND RUN CIRCUIT IN PCM SHORTED OUT DUE TO PCM FAILURE.LET DEALERSHIP OR GARAGE USE DIAGNOSTIC EQUIPMENT TO ACTIVATE THE PCM SEE IF IT HAS FAILED.DONT SPEND MONEY ON NEW PCM COULD BE SHORT IN THE WIRING CIRCUIT

Sep 06, 2011 | 1999 Oldsmobile Alero

1 Answer

My Alero heats up when I stop at a traffic light. Everything checks out ok. No leaks, new temp sensor, etc. Any ideas?


CHECK COOLING FAN SEE IF ITS RUNNING.IT NOT CHECK COOLANT FAN FUSE AND RELAY.IF ALL IS GOOD HOTWIRE COOLANT FAN SEE IF IT RUNS.IF NO REPLACE FAN.IF YES CHECK FAN WIRING AND CODE SCAN VECHICLE FOR PCM FAULT CODE.

Feb 26, 2011 | 1999 Oldsmobile Alero

1 Answer

Temp gauge often reads too hot, engine normal.


It sounds like your cooling fans are not comming on by themselves, but when you turn on the ac it forces them to turn on. Make sure relay is good, then replace coolant temp sensor, this may have failed no telling pcm to turn on cooling fans. Thanks

Jun 08, 2009 | 2002 GMC Safari

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