MAP sensor voltage is below the minimum threshold (typically below 0.5 V) when vacuum or boost conditions should produce a higher reading. The ECU incorrectly interprets a high-vacuum condition.
Common causes
Short to ground in the signal wire
MAP sensor failed low
Blocked vacuum port (carbon or condensation)
Connector corrosion
Symptoms
MIL illuminated
ECU interprets high vacuum/lean condition
Rich fuelling correction
Rough idle
Severity
Moderate severity: incorrect fuelling increases emissions and reduces driveability.