Computerized Engine Controls Flashcards

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:

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.

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:

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.

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

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.

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

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.

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

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.

The ECM enters open-loop operation when:

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.