P0102

P0102 means the MAF signal voltage or frequency is below the rationality floor — on an analog sensor that is typically under 0.2V key-on engine running, on a digital Hitachi/Bosch HFM frequency MAF that is below roughly 1.0 kHz at idle. This is almost always a wiring or power-supply fault, not a dead sensor. Cheapest-first ladder: back-probe the 12V or 5V supply wire at the MAF connector key-on (most GM/Ford MAFs need a 12V switched supply through the underhood fuse box, most import MAFs run on 5V from the ECM) — no power means a blown fuse or a melted PCM-fed relay contact; verify ground integrity by measuring voltage drop from the MAF ground pin to battery negative with the engine running, must be under 0.1V; with power and ground confirmed, jumper the signal wire to 5V momentarily and see if the scan tool reads a high MAF value — if yes, the wiring is good and the sensor is dead; airflow at idle reading 0.0 g/s with the engine clearly running is the signature of P0102 and confirms either no signal or no power. Do not replace the MAF before checking the fuse and the underhood relay — a $5 fuse fixes more P0102s than a $250 sensor on Ford trucks specifically.

Vehicle-specific patterns: 2004-2010 Ford F-150/Expedition 5.4L set P0102 when the underhood PDB fuse for the MAF/coil bank corrodes from water intrusion through the cowl drain; 2007-2013 GM Silverado/Sierra 5.3L set P0102 from a broken locking tab letting the MAF connector vibrate loose, intermittent before going hard-fault; 2005-2010 Chrysler/Dodge Hemi 5.7L sees P0102 from a chafed signal wire at the airbox-to-throttle-body bridge; 2003-2009 Toyota 4Runner/Tacoma 4.0L 1GR-FE sees P0102 from internal MAF failure where the sensor reads 0 g/s constantly and replacement is the only fix. Estimated repair: $5 to $350.