The fans only come on when i turn on the AC or unplug the ECT connector. I replaced the ECT and it's still the same. The PCM has 2.7 volts at pin 26 and 5 volts when i unplug the ECT connector. Is there any other sensors that the PCM controls, that can do this. When i first start the van cold it idles at 1300 RPMS, and after about 7 minuets it drops to 700 RPMS, and the heat gauge is at a 1/4 and rising. When i unplug the ECT, in a few seconds the fans come on and the RPMS go up, and the heat gauge drops to cold.
Hi Dave the ECU receives messages from sensors, one of which is a temperature sensor. When the sensor responds to a temp higher than the normal operating temp the fans are then and only then supposed to operate. They will switch in for a brief period and then turn off again. The idle speed is in direct relation to the cold start up idle requirements and specifications. When the engine is cold the idle speed will automatically increase and as the engine achieves operating temp, the idle speed will decrease inthe way you have recorded. If you start the engine and allow it to idle until normal temp is achieved the fan should cut in. The way you've desribed all systems are A okay!. Regards John
SOURCE: 2001 Chevy Venture Cooling Fans always running on high
either the temp sensor is bad but, it sounds like the fan relay is stuck.
replace the relay its in the fuse box.
SOURCE: Temperature sensor problem?
There are 2 different circuit that control the cooling fans.
The engine controller turns the low speed fan circuit on to control temperature and turns on the high speed fan circuit if the engine and A/C is running.
It sounds like your low speed fan function is not working.
Find your fan 1 fuse located in the under hood fuse panel and make sure it is not blown. If OK go to next step.
Find your fan 1 relay located in the under hood fuse panel. Find another relay in the fuse panel that matches and swap the two. If the fan then works you know you have a bad relay.
If both are check good, let me know and we will go from there.
Below, I have attached the wiring diagram for your cooling system, hope it helps.
Regards,
The cooling fan clutch actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, shearing of the fluid results in fan rotation.
The cooling fan clutch actuator valve is activated with a pulse width modulated (PWM) output signal from the powertrain control module (PCM). By opening and closing the fluid port valve, the PCM can control the cooling fan clutch speed. The cooling fan clutch speed is measured by a Hall-effect sensor and is monitored by the PCM during closed loop operation.
The PCM optimizes fan speed based on engine coolant temperature (ECT), engine oil temperature (EOT), transmission fluid temperature (TFT), intake air temperature (IAT), or air conditioning requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM monitors the fan speed through the Hall-effect sensor. If a fan speed increase is required, the PCM outputs the PWM signal to the fluid port, providing the required fan speed increase.
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