Question

1. two technicians are diagnosing an engine performance issue. the truck has a mil on with a code of p0128. technician a says a stuck open thermostat may be the cause. technician b says a faulty coolant temperature sensor may be the cause. who is correct?

a. technician a
b. technician b
c. both technicians
d. neither technician

1. at what speed will the pcm usually turn off electric cooling fans?______
2. all the following may cause the pcm to run the electric cooling fan on high except?

a. ect reaches 110 degrees c
b. a/c refrigerant pressure exceeds 240psi
c. vehicle is moving over 60mph
d. certain dtcs are set

1. the coolant temp warning light comes on when the ect reads between __ and __ degrees.
2. a radiator has been replaced and now the customer complains of a poor idle. the technician notices erratic temperature readings from the ect while monitoring current data. what is the most likely cause?

a. air in the cooling system
b. collapsed upper radiator hose
c. wrong coolant used
d. radiator cap installed incorrectly.

1. when the engine is hot, where does the excess coolant go when it expands in the radiator?

a. drains on the ground
b. gets trapped in the radiator
c. into the surge tank
d. none of the above

1. air in the cooling system will cause all the following concerns except

a. erratic temperature readings
b. poor heater operation
c. cooling fan failure
d. overheating

1. what is the purpose of a coolant bypass/ bypass hose?
2. which of the following cooling system configurations is the least likely to form galvanic corrosion?

a. aluminum radiator, cast iron block and cast - iron head
b. aluminum radiator, aluminum block, and an aluminum head
c. aluminum radiator, cast iron block, and an aluminum head
d. brass radiator, cast iron block and a cast iron head.

Explanation:

Step1: Analyze question 1

A stuck - open thermostat and a faulty coolant temperature sensor can both cause engine performance issues related to the code P0128. So both technicians are correct.

Step2: Analyze question 2

The PCM usually turns off electric cooling fans when the vehicle is at a lower speed or when the engine temperature is within an acceptable range. When the vehicle speed is high enough, the air flow through the radiator due to vehicle motion can be sufficient for cooling, so the PCM may turn off the electric fans.

Step3: Analyze question 3

When the vehicle is moving, the air flow through the radiator helps in cooling and the PCM is less likely to run the electric cooling fan on high just because the vehicle is moving. ECT reaching a high temperature, A/C refrigerant pressure being high, and certain DTCs can cause the PCM to run the fan on high.

Step4: Analyze question 4

The coolant temperature warning light comes on when the ECT (Engine Coolant Temperature) reads between 220 - 230 degrees in many vehicles.

Step5: Analyze question 5

Air in the cooling system can cause erratic temperature readings from the ECT sensor as it affects the proper circulation and heat transfer of the coolant.

Step6: Analyze question 6

When the engine is hot and the coolant expands in the radiator, the excess coolant goes into the surge tank.

Step7: Analyze question 7

Air in the cooling system can cause erratic temperature readings, poor heater operation, and overheating. But it is not likely to cause cooling fan failure directly.

Step8: Analyze question 8

The purpose of a coolant bypass/bypass hose is to allow coolant to circulate around the engine when the thermostat is closed, to warm up the engine more quickly.

Step9: Analyze question 9

Galvanic corrosion occurs when two different metals are in contact in the presence of an electrolyte. When all components (radiator, block, and head) are made of the same metal (such as all - aluminum), the likelihood of galvanic corrosion is the least.

Answer:

1. c. Both Technicians
2. When vehicle speed is high enough
3. c. Vehicle is moving over 60mph
4. 220, 230
5. a. Air in the cooling system
6. c. Into the surge tank
7. c. Cooling fan failure
8. To allow coolant to circulate around the engine when the thermostat is closed
9. b. Aluminum radiator, aluminum block, and an aluminum head