Service Section Technical Pages

VEHICLE DIAGNOSTICS : Engine Management

Modern vehicles have complex engine management systems designed to increase engine efficiency and reduce harmful exhaust gas emissions.

The engine control computer module compares values from various sensors to calculate;

  • Driver demand

    • Throttle position sensor, brake pedal switch, clutch switch,etc

  • The relative position of mechanical engine components
    • using Crankshaft position sensor & Camshaft position sensor,
  • Temperature :

    • How hot or cold the engine is (intake air temperature,coolant temperaure)
  • Engine speed and load

    • airflow sensor, manifold absolute pressure (vacuum) , turbocharger boost pressure
  • Exhaust emissions

    • (Lambda or Oxygen sensor fault code may occur)
  • Exhaust Gas Recirculation (EGR)


    • Condition Monitoring

    The engine control unit of a modern vehicle is capable of condition monitoring of system components . Faults may be logged by the engine management control unit and stored as fault codes in memory. The fault codes can later be read using a diagnostic tool . Faults may be indicated to the vehicle driver by the illumination of an engine management light (MIL) on the vehicle instrument panel.

    Test and Repair

    Following testing, a faulty wiring circuit may be repaired or component cleaned or replaced.
    Diagnostic Equipment Functions
    Our diagnostic equipment is capable of

  •   Fault code reading
  •   Actuator testing

    • to verify wiring circuits by operating the suspect component on a wide range of vehicle systems. The actuator test function can allow some components to be thoroughly cleaned which may save replacement cost.
  • Programming and Coding

    • Some components such as electronic fuel injectors , throttle bodies etc may need coding to the vehicle ecu
  • Advanced system testing can be carried out using oscilloscope signal test methods
  • Reset Procedures

    • Following repair work the fault code memory of the vehicle computer will need to be reset to clear stored fault codes.

     

    Sensors, Actuators , and Common Faults

    Mechanical  Position and Speed sensors :

    Cam position sensor : used to identify cylinder phasing. A cam sensor failure may prevent engine starting

    Crankshaft (CKP)position sensor : Identification of engine crankshaft position and calculation of engine speed and combustion forces. Frequency and amplitude signal is proportional to engine rotational speed.

    Typical failure : Signal errors can occur due to failed sensor , phonic wheel damage, or wiring connection failure.cranksensor.jpg

    Vehicle speed sensor provides input to sense vehicle speed which may be taken from gearbox sender, axle speed sender ,or antilock braking wheel speed sensor..

    Driver Input Sensors

    Throttle position sensor (TPS) / Accelerator Position sensor (APP)
    function:    Driver demand signal. TPS  failure may occur due to wear of potentiometer track causing flat spots and hesitation when accelerating.

    Brake Pedal Position & Clutch Pedal Position sensors used to reduce to stabilise idle speed and fuel delivery quantity when  engine is off load . Faults may occur due to worn out switches resulting in false (implausible) signals.

     

    Temperature Sensors

    Intake Air Temperature Sensor may be incorporated with air mass meter , with MAP sensor (T-MAP) or seperate.

    Coolant Temperature Sensor measures temperature of engine coolant and may be used to provide signal to control unit to activate cooling fan or adjust fuelling from cold start to warm up.Temperature signal is processed to compensate engine smooth running by control of fuel delivery  egr position, & diesel pre heat function.

    Flow Sensors

    Mass Air Flow (MAF) sensor measures volume of air entering air intake , Air Mass Meter measures weight of air entering intake tract. Engine load sensor which can effect fuel metering (petrol engine) or EGR position (diesel engines) . Typical fault code P0100

    Exhaust gas recirculation ( EGR ) system functions to reduce combustion temperature and oxides of Nitrogen ( Note : not Nitrous oxide !) EGR and Idle speed control ( ISC ) devices are particularly prone to failure due to build up of carbon and soot deposits which can restrict the air inlet system of the engine.

    EGR systems may cause the MIL warning lamp to illuminate intermittently and flag a P0400 EOBD fault code due to "critical system malfunction" as described on certain diagnostic equipment !

    Pressure and Vacuum Sensors

    Manifold Absolute Pressure (MAP) sensor measures engine load by vacuum (petrol engines) or boost pressure (turbocharged engines) at intake manifold. Split or blocked pipes can effect operation. MAP signal can influence fuel control, EGR, and turbo boost.

    Fuel Delivery System :  Low and high pressure fuel injection pumps, pressure regulator, fuel injectors. Prone to faults caused by fuel contamination , and general wear.

    Boost pressure control : turbocharger waste gate position and hence boost pressure control is often actuated by solenoids controlling vacuum circuits. Common faults can include loss of vacuum due to vacuum pump wear, split or blocked vacuum pipes, electrical circuit faults with control, solenoid or wiring.

     Exhaust Emissions Sensor

    Lambda Sensor (fitted to Petrol & Gas fuel systems)
    Measures oxygen content of exhaust gas and is used as a feedback signal to control fuel quantity delivery. Can deteriorate due to age and contamination. Lambda sensor fault codes may also relate to problems other than the sensor itself. Lambda sensor operation can is affected by sensor temperature .Lambda sensor feedback signal is only used when engine operating temperature is sufficient to enable closed loop control status.
    A second lambda sensor may be fitted in the exhaust system after the catalytic converter to monitor condition of the catalyst.

    Actuators

    Fuel injectors

    EGR valve

    Throttle Motor

    Solenoids

    Turbocharger wastegate controller