ASE4 Computerized Engine Controls 1 — Questions and Answers
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:
- Reading too low, causing the ECM to add fuel
- Reading too high (high pressure), causing the ECM to add excess fuel (Correct answer)
- Within normal range for altitude compensation
- Causing a lean condition
Correct answer: Reading too high (high pressure), causing the ECM to add excess fuel
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:
- Open circuit, defaulting to a maximum cold reading (Correct answer)
- Shorted to ground, reading hot air temperature
- Correct — the sensor reads ambient temperature as cold
- Reporting a lean condition signal
Correct answer: Open circuit, defaulting to a maximum cold reading
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?
- MAP sensor
- MAF sensor
- Upstream oxygen (O2) sensor (Correct answer)
- IAT sensor
Correct answer: Upstream oxygen (O2) sensor
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:
- The sensor is faulty and must be replaced
- Normal operation within typical range (Correct answer)
- The sensor is providing a biased signal
- The ECM will default to open-loop control
Correct answer: Normal operation within typical range
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:
- Enrich the fuel mixture as if the engine is cold
- Lean out the mixture as if the engine is fully warm (Correct answer)
- Activate cold-start enrichment strategies
- Disable the EGR system
Correct answer: Lean out the mixture as if the engine is fully warm
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.
Question 6: The ECM enters open-loop operation when:
- The O2 sensor is sending accurate voltage signals
- The coolant temperature is below the closed-loop enable threshold (Correct answer)
- Both fuel trims are at 0%
- The catalytic converter is at operating temperature
Correct answer: The coolant temperature is below the closed-loop enable threshold
Open-loop operation occurs during cold start when the coolant temp is below the threshold for reliable O2 sensor feedback.
ASE4 Computerized Engine Controls 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: