Question: I own a 2003 GMC Envoy XL with the 4.2-liter six-cylinder engine. I live in the Middle East, in Beirut, Lebanon. Due to an ongoing problem with the cooling fan clutch (four failed clutches in eight months’ time), I decided to switch to an electric-fan setup. As I live outside the USA, I have no access to kits available in the U.S. I used an electric fan from a Mercedes-Benz S-Class car with a fan speed controller, thermostat, and A/C control. The system works fine, but because the original fan clutch and fan are gone, the service-engine light remains lit. What can I do to trick the Envoy’s computer into thinking that the original fan is still there? Is there a company that sells a part that hooks to the fan clutch plug to mimic the presence of the clutch? I get the feeling that the Envoy’s mileage is suffering due to the service-engine light remaining lit. I was told that, when the service engine light is lit, the Envoy would not drive properly as the computer switches into limp mode. Are these two statements correct?

Answer: I don’t know of any way to mimic the presence of the fan clutch. The “electro-viscous” fan clutch actually emits a fan speed signal to the Powertrain Control Module. And yes, when the service-engine light comes on, the PCM will use default control parameters to prevent damage to the powertrain and get you home safe. What I don’t understand is going through four fan clutches in eight months. I know it gets hot in that part of the world, but there has to be more to the story. You may want to go back to the original fan clutch, or a combination of both. A standard coolant fan clutch is thermostatically controlled and engages the fan according to underhood temperature. An electro-viscous fan clutch is very similar but controlled electronically by the PCM, which determines engagement (fan speed) once analyzing data including coolant temperature, A/C refrigerant pressure, vehicle speed, intake air temperature, transmission fluid temperature, and ambient air temperature. Check with a GMC dealer or customer service on related Technical Service Bulletins, which may help with your repeat failure problem -- there are several. They cover issues such as fan clutch wiring harness damage causing a service engine light, A/C performance, and a ticking noise.

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