ASE A8 Engine Performance Practice Test

Diagram of automotive PCM engine control system.

6. An engine has a rich air-fuel ratio. There is excessive resistance found at point A in the schematic diagram above. All of the following statements regarding this circuit are true EXCEPT:

  • A. Point A is the ground connection for an (NTC) negative temperature coefficient sensor.
  • B. Too much resistance at point A will result in delayed torque converter engagement.
  • C. Too much resistance at point A will result in delayed engine cooling fan operation.
  • D. The ECM provides a 12-volt reference signal.

6.

Answer A is wrong. Point A is the ground connection for the Engine Coolant Temperature Sensor, an (NTC) negative temperature coefficient sensor. The engine runs a startup strategy that enriches the air-fuel ratio when the engine's coolant is cold. These sensors have less resistance as temperature increases.

Answer B is wrong. The ECT sensor affects several different systems, like air conditioning and transmission. This signal affects EGR flow, enrich fuel mixtures, and delay torque converter, or A/C compressor engagement.

Answer C is wrong. The ECM uses different strategies programmed into its lookup tables for hot and cold operating conditions. This resistance results in delayed engine cooling fan engagement.

Answer D is correct. This is an EXCEPT-type question. The (ECT) engine coolant temperature sensor is a variable resistor that uses resistance to change a 5-volt reference signal from the ECM.