2002 ENVOY
Question:
As usual, a very informative and helpful post!
– Hide quoted text — Show quoted text -> "Mike Levy"wrote > I’d like to see how they rig THAT wire. That fan clutch is filled > with a fluid that changes viscosity with temperature. HOW will a > software update do ANYTHING to adjust the fan clutch… > This is probably because you have not seen what "these" > fan clutch’s look like. This is a different beast then what > you are probably used to. It in fact has wiring connections > to the fan/fan clutch assembly. In fact, you can unscrew > the fan clutch and fan assembly from the water pump > like any other vehicle, but you can’t get the fan out as > it’s hard wired to shroud assembly. > Here is a blurb from the service manual on how it works: > The purpose of the electro-viscous (EV) fan clutch is to maintain powertrain > cooling requirements. The powertrain control module (PCM) monitors the > following sensors to regulate the fan speed; > a.. Engine coolant temperature sensor > b.. A/C refrigerant pressure sensor > c.. Vehicle speed sensor > d.. Intake air temperature sensor > e.. Transmission fluid temperature sensor > f.. Ambient air temperature sensor > The PCM controls the electro-viscous fan clutch engagement. The PCM > regulates a 12-volt pulse width modulated signal (PWM) to the cooling fan > relay. The PWM signal determines the ON time of the relay. As the commanded > state of the fan clutch increases, so does the ON time of the relay. This ON > time directly effects the amount of time the solenoid, which is internal to > the fan clutch, is energized. When the solenoid in the fan clutch is > energized, it opens the spring loaded valve and allows fluid to flow from > the storage chamber to the fluid coupling of the cooling fan clutch, > increasing the fan speed. When the solenoid is de-energized, the spring > loaded valve closes, and blocks the path of the fluid to the fluid coupling > of the fan clutch, reducing fan speed. > The fan has the ability to create a feedback signal, so the PCM has an > actual fan speed input. This is done with a hall effect sensor internal to > the fan clutch. The PCM supplies a 5-volt reference and a low reference to > the hall effect sensor. The hall effect sensor returns a signal pulse > through the cooling fan speed signal circuit in response to the reluctor > track passing by the magnetic field of the hall effect sensor. > The PCM commands the cooling fan to 100% under the following conditions: > a.. Engine coolant temperature exceeds approximately 129
