Diagnostic Aids

WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

This test is intended to diagnose the following:

MAF sensor.
Harness circuits: MAF SIG, MAF RTN, vehicle power (VPWR), and power ground (PWR GND).
PCM.

The mass airflow sensor measures the airflow rate into the engine and provides an analog signal to the Powertrain Control Module (PCM). The PCM regulates the quantity of fuel injected into the engine, thus controlling the air fuel ratio.

Current PCM implementation contains a mass airflow interface, which consists of a two pole, differential input, low pass filter. This filter is designed to pass an analog signal, originating from the mass air sensor, while rejecting unwanted ignition noise, high frequency electrical interference, and ground offsets.

The input to the interface is the analog voltage signal difference between MAF+ (mass airflow signal) and MAF- (mass airflow signal return). The MAF sensor outputs an analog voltage signal calibrated to 0.5 V at the lower limit of the flow range and 4.75 V at the upper limit of the flow range.