ASE4 Computerized Engine Controls

Question 1

A MAP (Manifold Absolute Pressure) sensor reads 4.8 volts at idle. Normal is approximately 1.0–1.5 volts. The engine runs rich. This indicates the MAP sensor is:

Accepted Answer

Reading too high (high pressure), causing the ECM to add excess fuel

Answer

A MAP sensor reading high voltage at idle tells the ECM the manifold pressure (load) is high, causing it to add excess fuel and enrich the mixture.

Question 2

An IAT (Intake Air Temperature) sensor reads -40°F in ambient temperature of 70°F. The engine cranks hard and runs rich when cold. This indicates the IAT sensor is:

Accepted Answer

Open circuit, defaulting to a maximum cold reading

Answer

An open IAT sensor circuit defaults to the coldest possible value (-40°F), causing the ECM to enrich the mixture as if starting in extreme cold.

Question 3

Which sensor is MOST responsible for closed-loop fuel control correction?

Accepted Answer

Upstream oxygen (O2) sensor

Answer

The upstream O2 sensor provides real-time feedback on exhaust oxygen content that drives the ECM's closed-loop fuel trim corrections.

Question 4

A TPS (Throttle Position Sensor) reads 0.3 volts at closed throttle and 4.8 volts at WOT. These values indicate:

Accepted Answer

Normal operation within typical range

Answer

TPS voltage typically ranges from about 0.2–0.5V at closed throttle to 4.5–4.9V at WOT, making these readings within normal parameters.

Question 5

A CTS (Coolant Temperature Sensor) stuck at a high-temperature reading will cause the ECM to:

Accepted Answer

Lean out the mixture as if the engine is fully warm

Answer

A CTS biased to high temperature tells the ECM the engine is hot, so it reduces the cold-start enrichment, potentially causing lean and hard-start issues.

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 Computerized Engine Controls