computer fundamentals

Computer Adjustments and Functionality

• Adjustment Mechanism

  • Computers in vehicles make adjustments based on sensor readings.
  • Example:
    • If the coolant temperature (ECT) is at a certain level, the computer determines how much fuel to supply.
  • The computer interprets these inputs similar to a person viewing data on a spreadsheet, taking action when everything operates correctly.

• Default Mode Activation

  • If a critical sensor (e.g., ECT sensor) fails, the computer enters default mode.
  • Behavior in Default Mode:
    • It will try to function without the ECT sensor:
      • Relies on other sensors for fuel management (e.g., air fuel sensors).
    • Prompts the computer to limit fuel to avoid system overload.

• Memory and Learning Capabilities

  • Computers in vehicles, such as PCM (Powertrain Control Module), have memory storage (ROM, EEPROM, RAM).
  • They retain past performance data, thus learning how a driver typically operates:
    • Example:
      • If a driver accelerates aggressively, the transmission will shift harder in response.
  • Resetting PCM:
    • When a used vehicle is purchased, resetting the PCM ensures it no longer remembers previous driving habits.

• Input and Output Functions of the Computer

  • The computer receives input from different sensors, such as:
    • Throttle Position Sensor (TPS):
      • TPS sends a voltage signal indicating throttle position, ranging from 0.5 volts to 4.5 volts.
      • If the TPS is malfunctioning (shorted), the computer may misinterpret the throttle input leading to unintended acceleration.
  • Outputs include control signals for:
    • Idle air control valves
    • Electronic throttle body
    • Intake manifold runner control (IMRC)

• Sensor Communication

  • Cars utilize CAN (Controller Area Network) communication for efficient data transfer between modules.
  • CAN communication characteristics:
    • Low speed and high-speed communication modes.
    • Voltage levels for CAN low (2.47 volts) and CAN high (2.54 volts).

• Diagnostics and CAN Communication Failures

  • If communication fails, the diagnosing process may involve checking each control module one at a time.
  • Diagnosing is challenging; failure of one module can impact numerous systems.

Input Sensors and Their Functions

• Common Sensor Types
  • Engine speed sensors (e.g., crankshaft or camshaft position sensors)
  • Throttle position sensor (TPS)
  • Vehicle speed sensor (VSS), often sourced from ABS in modern vehicles
  • Exhaust gas oxygen (O2) sensors
• Differences in sensor tech:
  • Older cars have separate VSS, while modern vehicles typically integrate this function into ABS systems; problems in ABS can lead to loss of speed data.

Output Functions and Control

• The PCM manages a variety of vehicle functions and systems, including:

  • Fuel injectors
  • Idle speed control via various types of control valves.
  • Control modules for emissions and transmission shifts.

• Pulse Width Modulation (PWM)

  • PWM operates like a switch, rapidly turning an output on and off to control devices (e.g., controlling fuel pumps).
  • Output may vary:
    • A 50% duty cycle will demonstrate half the possible voltage.
  • Recommended tool for measuring PWM is an oscilloscope, which provides accurate representations of duty cycles and input signals.

Computer Architecture

• Components of Vehicle Control Computers

  • CPUs, Memory, and Communication Protocols:
    • Similarities to desktop computers in terms of architecture and functions.
    • Computer must process input data rapidly to respond effectively.

• Tuning and Adjustments

  • Vehicle tuners can modify the computer's functions, optimizing performance:
    • Adjustments can involve changing ignition timing, fuel-air mixtures, and boost levels for turbocharged engines.
  • Tuning schools exist to provide education on performance tuning.

Safety and Location Concerns for Control Modules

• Locations of ECUs
  • Control modules might be found under the dash, hood, or transmission tunnel:
    • Noteworthy instances of poor design:
      • 2004-2008 TSX models: module placed directly beneath an AC drain leading to moisture problems.
  • Common issues include module damage from water intrusion, corrosion in terminals, and impact from environmental factors.

Emissions Control and EVAP Systems

• Emissions diagnostics can be particularly challenging due to complex systems:

  • Common errors in older emissions diagnostic processes involved checking gas caps, which are now eliminated in many new models without cap systems.
  • Focus on the expanding complexity of EVAP systems and the array of potential failure points:
    • Importance of identifying leaks in various components, which may go unnoticed without proper diagnostics.

• Common Error Codes

  • Codes like PO 455 or PO 456 indicate EVAP leaks.
  • Technicians now need to check various lines and connectors for leaks due to the absence of gas caps.

Troubleshooting and Repair Practices

• Utilizing appropriate tools and methods is crucial for diagnosing electrical issues:

  • When working with output drivers, use relays to safely manage high current loads and prevent overheating or damage.
  • Identification of electrical problems often requires knowledge of duty cycles and how PWM functions within the control circuits.

• Best Practices for Repairs

  • Always use relays for high-amperage devices (e.g., fuel pumps) to prevent damaging the PCM.
  • Understanding how to read oscilloscope data effectively; it provides detailed insights into circuit behavior that standard multimeters cannot capture.

• Concluding Remarks

  • The integration of connectivity between modules via high-speed communication allows modern automotive systems to function seamlessly when properly maintained.
  • Awareness of the vulnerabilities of electronic components helps technicians take proactive measures against common issues in vehicle design and electronics.