20.) A vehicle has poor fuel economy and insufficient heat from the HVAC system. Which of these could be the cause? OA. A failed HVAC blower motor OB. A failed radiator cooling fan motor C. A stuck-open thermostat OD. A stuck-closed thermostat

## Step 1<br />The problem presents a situation where a vehicle is experiencing poor fuel economy and insufficient heat from the HVAC system. The task is to identify the potential cause of these issues from the given options.<br /><br />## Step 2<br />Option A suggests that a failed HVAC blower motor could be the cause. However, a failed HVAC blower motor would not directly affect the vehicle's fuel economy. It would only affect the HVAC system's ability to distribute heat, which is not the issue in this case.<br /><br />## Step 3<br />Option B proposes that a failed radiator cooling fan motor could be the cause. This would not directly affect the vehicle's fuel economy either. It would only affect the cooling system's ability to cool the engine, which is not the issue in this case.<br /><br />## Step 4<br />Option C suggests that a stuck-open thermostat could be the cause. This could lead to poor fuel economy because the engine would have to work harder to maintain the desired temperature, consuming more fuel. However, it would not result in insufficient heat from the HVAC system.<br /><br />## Step 5<br />Option D suggests that a stuck-closed thermostat could be the cause. This could lead to both poor fuel economy and insufficient heat from the HVAC system. The thermostat would not allow the engine to cool down, causing the engine to overheat. This would force the air conditioning system to work harder to cool the engine, leading to poor fuel economy. Additionally, the HVAC system would not be able to produce sufficient heat because the engine is already overheating.