Powertrain Controls - ECM/PCM

DTC 48 Chart:

MAF Sensor Circuit:

CIRCUIT DESCRIPTION
The Mass Air Flow (MAF) sensor measures the amount of air that flows into the vehicles' engine. This information is required by the engine's Powertrain Control Module (PCM) to schedule fuel and maintain the desired air/fuel ratio.

The MAF sensor used on this vehicle is a hot wire type and is used to measure air flow rate. The MAF output frequency is a function of the power required to keep the air flow sensing elements (hot wires) at a fixed temperature above ambient temperature. As air flows through the MAF sensor, the "hot wires" are cooled. The amount of cooling is proportional to the rate of air flow. As air flow increases, a greater amount of current is required to maintain the "hot wires" at a constant temperature. The MAF sensor converts the changes in current draw to a frequency signal read by the PCM. The PCM calculates air flow (grams per second) based on this signal.


DIAGNOSTIC TROUBLE CODE (DTC) 48 WILL SET WHEN
The PCM detects engine reference pulses without detecting a frequency signal from the MAF sensor.

ACTION TAKEN (PCM DEFAULT)
The Malfunction Indicator Lamp (MIL) will illuminate and speed density will be used for fuel management.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This step will determine if the fault is a hard failure or an intermittent condition.

2. This step checks for a 5 volt reference from the PCM.

3. Verifies that both ignition voltage and a good ground circuit are available.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation, or a broken wire inside the insulation.

A DTC 48 could be caused by a vacuum leak. Check short and long term fuel trim for being in the optimal range (both banks).