3.1 PRIMARY SIGNAL TYPES FOUND IN MODERN VEHICLES
Once you become familiar with basic vehicle waveforms it will not matter how new or old the vehicle is, or even who
manufactured the vehicle. You will be able to recognize signals that do not look right.
Direct Current (DC) Signals
The types of sensors or devices in a vehicle that produce DC signals are:
• Power Supplies - Battery voltage or sensor reference voltages created by the PCM.
• Analog sensor signals - engine coolant temperat ure, fuel t emperature, intake air temperature, throt tle position,
EGR pressure and valve position, oxygen, vane and hot wire mass airflow sensors, vacuum and throttle switches
and GM, Chrysler and Asian manifold absolute pressure (MAP) sensors.
Alternating Current (AC) Signals
The types of sensors or devices in a vehicle that produce AC signals are:
• Vehicle speed sensors (VSS)
• Antilock brake system wheel speed sensors (ABS wheel speed sensors)
• Magnetic camshaft (CMP) and crankshaft (CKP) position sensors
• Engine vacuum balance viewed from an analog MAP sensor signal
• Knock sensors (KS)
Frequency Modulated Signals
The types of sensors or devices in a vehicle that produce Frequency Modulated signals are:
• Digital mass airflow (MAF) sensors
• Ford’s digital MAP sensors
• Optical vehicle speed sensors (VSS)
• Hall Effect vehicle speed sensors (VSS)
• Optical camshaft (CMP) and crankshaft (CKP) position sensors
• Hall Effect camshaft (CMP) and crankshaft (CKP) position sensors
Pulse Width Modulated Signals
The types of circuits of devices in a vehicle that produce Pulse Width Modulated signals are:
• Ignition coil primary
• Electronic spark timing circuits
• EGR, purge, turbo boost, and other control solenoids
• Fuel injectors
• Idle air control motors and solenoids
Serial Data (Multiplexed) Signals
The types of circuits or devices in a vehicle that produce Serial Data signals are:
• Powertrain control modules (PCM)
• Body control modules (BCM)
• ABS control modules
• Other control modules with self diagnostics or other serial data / communications capability
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3. AUTOMOTIVE ELECTRONIC SIGNALS
