Introduction
NOTE:
The information, specifications and illustrations in this section are based on the use of a Snap-On Scanner. This information can be used to interpret information displayed by scanners from other manufacturers, if there is any question concerning data displayed refer to manufacturers operating instructions.
SCANNER MENU
In the CODES & DATA and sensor and switch test menu selections, the scanner displays engine operating parameters from the vehicle logic module. On most 1988 and later Chrysler products, the logic module is part of the single module engine controller (SMEC) or single board engine controller (SBEC). The logic module operation in all systems is basically the same, however.
LOGIC MODULE SIGNALS
It receives and processes input signals from sensors and sends output signals to actuators:
- Input parameters are signals from various sensors and switches to the logic module.
- Output parameters are commands from the logic module to various actuators, such as solenoids and fuel injectors.
TYPES OF SIGNALS
All 1988 and earlier systems display only analog data parameters. Starting in 1989, most systems also display digital (discrete) parameters in addition to analog values. Analog and digital (discrete) parameters are explained on the next page.
- Analog parameters are quantities displayed as a measured value in the appropriate units. Voltage, pressure, temperature, time, and speed parameters are examples of analog values. The scanner displays them as numbers that vary through a range of values in specific units, such as voltage (v), pounds per square inch (psi), kilopascals (kPa), degrees Celsius (°C), degrees Fahrenheit (°F), or miles per hour (mph).
Digital (Discrete) parameters are those that can be in only one of two states, such as on or off, open or closed, high or low, yes or no. Switches and solenoids provide discrete parameters on 1989 and later vehicles. The scanner displays discrete parameters as ON/OFF, YES/NO, OPEN/CLAST, HI/LO, or some other readings that indicate alternate states.
SCANNER DISPLAY
The scanner can display some parameters in numbers that range from 0 to 255, 0 to 9999, or some other range. These ranges are used because in each case, it is the maximum number range that the logic module can transmit for a given parameter. Some parameter readings, however, will never reach the highest possible number. For example, you will never see a vehicle speed parameter reading of 255 mph.
ENGINE DATA GROUPS
Engine data parameters can be grouped in the categories listed below in relation to engine and vehicle systems. During troubleshooting, several parameters from two or more categories often must be evaluated together for accurate diagnosis
1. General - General parameters are those that affect several different vehicle systems. These include engine and vehicle speed and exhaust oxygen (02) sensor operation.
2. Fuel delivery - Fuel delivery parameters indicate how the logic module is controlling the carburetor or fuel injection. When the engine is warm and running in closed loop, the logic module controls the air/fuel ratio based on signals from several engine sensors. The logic module controls fuel metering with output signals to the fuel injectors or the feedback carburetor solenoid.
3. Throttle position and Idle control - Throttle position and idle control parameters indicate the position of the throttle and the way in which the logic module is controlling idle speed.
5. Air (barometric) pressure, manifold pressure, and turbocharger - These parameters are input signals to the logic module that measure the atmospheric air pressure and the absolute pressure within the intake manifold. The logic module uses them primarily for fuel delivery and spark timing calculations.
6. Electrical and Ignition parameters - Electrical parameters are voltage measurements for various circuits, such as battery voltage. ignition parameters are those that affect spark timing calculations. The ignition module controls spark timing when the engine is cranking and immediately after starting. After electrical power has stabilized, the logic module controls spark timing and sends timing control signals to the ignition module. The logic module uses various sensor signals to increase (advance) or decrease (retard) timing.
Some vehicles also have a system that uses signals from a detonation sensor to decrease spark timing when engine knock occurs.
7. Temperature - These parameters indicate the temperature of the engine coolant, the intake air, the ambient air, and the fuel in the fuel injection system. The logic module uses them for fuel delivery calculations on many engines.
8. Emissions - Emissions parameters are those that indicate the operation of emission controls, such as air injection and exhaust gas recirculation (EGR).
9. Transmission and cruise control - These parameters are all of the switch and sensor signals from the transmission to the logic module and the output commands from the logic module to transmission solenoids. Most of these input parameters are discrete signals that let the logic module know what gear the transmission is in. Many transmissions are not the same from vehicle to vehicle, and some gear switch signals may not be active.
10. Heating, ventilating, and air conditioning (HVAC) - HVAC parameters indicate input and output signals between the logic module and various components.
FOLLOWING SECTIONS
The following sections explain the data parameters displayed by the scanner for Chrysler vehicles. Because the vehicle logic module determines the parameter data list, not all parameters listed are displayed for every car or truck.
Each parameter description lists the parameter title and value as displayed on the scanner. This is followed by the full title and a description of the states for discrete parameters or a description of the measurement units and ranges for analog parameters.