I am having similar issues. Have a 99 Pontiac Grand am. Has the dual fans. I have ruled out tstat, relays, grounds, etc by using a scan tool and testing both the low speed and high speed fan switches and fans come on. So immediatly I think its the sensor or the wiring but the thing is, the ECU is getting a coolant temperature reading and it is registering on both the scan tool and the gauge in the car.

Is there another sensor that controls the fans or does this car rely on all 1 sensor? The vehicle in question is a 99 Grand AM with the 3400 in it.

If anyone can help direct me in the right way, that would be great.
For shits and giggles, I am going to replace the engine coolant temp sensor and see if that works. WHile doing so, I will check for voltage at the ECU even though that should turn up fine as the ECU is getting a coolant temp signal to begin with.

I am having similar issues. Have a 99 Pontiac Grand am. Has the dual fans. I have ruled out tstat, relays, grounds, etc by using a scan tool and testing both the low speed and high speed fan switches and fans come on. So immediatly I think its the sensor or the wiring but the thing is, the ECU is getting a coolant temperature reading and it is registering on both the scan tool and the gauge in the car.

Is there another sensor that controls the fans or does this car rely on all 1 sensor? The vehicle in question is a 99 Grand AM with the 3400 in it.

If anyone can help direct me in the right way, that would be great.
For shits and giggles, I am going to replace the engine coolant temp sensor and see if that works. WHile doing so, I will check for voltage at the ECU even though that should turn up fine as the ECU is getting a coolant temp signal to begin with.

Your 99 is no where near the same as the 96 grand am. Your post is being moved to its own thread.

If the temp gauge is reading and your scann tool says its right, then check your fuses and replace the relays(2) for these fans. I would also check the plug on the AC on the bottom of the engine. :thumbsup:
Also thier is a wire diagram in the Tips and Maintenance (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2148)section.

Your 99 is no where near the same as the 96 grand am. Your post is being moved to its own thread.

If the temp gauge is reading and your scann tool says its right, then check your fuses and replace the relays(2) for these fans. I would also check the plug on the AC on the bottom of the engine. :thumbsup:
Also thier is a wire diagram in the Tips and Maintenance (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2148)section.

Why would you tell me to check the relays and fuses when that clearly isnt the issue? The scan tool activates both fans so that rules out fuses and relays as the fans are getting power.

Put in a new engine coolant sensor and everything works. The sensor acts as a trigger and was reading to low. Just because it registed on the ecu and dash, doesnt mean it was accurate. car was overheating before fans would turn on.

all fixed.