P0107MAP sensor circuit low input

Is the hard low-input cousin of MAP faults: the ECM sees manifold pressure voltage or calculated kPa stuck below the valid window—often near ground. Drivers get a check-engine light, a limp or overly rich/lean feel depending on how the controller fails safe, and sometimes a no-start or hard-start when speed-density fueling is based on a bogus low MAP. Freeze frame typically shows a very low MAP PID at key-on or idle that never climbs toward baro on tip-in.

Most shops find an open signal wire, a MAP connector unplugged after intake service, or a short to ground on the signal circuit first. Next come a failed MAP sensor that outputs near-zero volts with good 5 V reference, a missing sensor ground that collapses the reading, or a vacuum hose pulled off so the sensor sees a weird atmospheric/port condition that some ECMs still flag as low circuit after rationality checks. Shared 5 V reference shorts that pull the rail down can make MAP and other sensors look dead together—do not replace three sensors before you meter the reference.

Diagnosis ladder: key-on measure reference, ground, and signal at the MAP connector. Reference should be ~5 V; ground near 0 V; signal should sit in a believable mid-range KOEO (near baro). If signal is stuck near 0 V with the sensor plugged in, unplug and recheck—if the wire rises, the sensor is shorted low; if it stays low, the harness is shorted to ground. Confirm the vacuum hose is seated only after the electrical path is honest. Replace the MAP when reference and ground are good and the sensor still will not produce a rising signal under vacuum change or KOEO baro. Dig elsewhere when multiple sensors share a dead 5 V rail, when the connector was left half-latched after a manifold job, or when P0106 returns after a low-circuit repair because the hose is still soft. System context: low MAP input corrupts load calculation on speed-density engines and confuses baro updates on MAF cars—restore the circuit before chasing fuel pressure.