Audi A4, S4

since 2000 release

Repair and operation of the car


Audi A4, S4
+ Introduction
+ Governing bodies and methods of safe operation
+ Current leaving and service
+ Engine
+ Cooling systems, heating and air conditioner
+ Power supply systems, release and decrease in toxicity of the fulfilled gases
- Systems of electric equipment of the engine
   + System of ignition and engine management
   + System of preheat of the diesel engine
   - Diagnostics of systems of electronic control and diagnostic equipment
      General information
      Diagnostics of electronic control systems of the engine, injection, ignition and auxiliary brake systems
      The controler of interface of the personal computer to onboard system of self-diagnostics of OBD II under protocols of the SAE standards (PWM and VPW) and ISO 9141-2
      Application of an oscillograph for supervision of signals in chains of control systems
   + Systems of charging and start
+ Manual box of gear shifting
+ Automatic transmission
+ Coupling, power shafts and differential
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment





Application of an oscillograph for supervision of signals in chains of control systems

Digital multimeters perfectly are suitable for check of the electric chains which are in a static state, and also for fixing of slow changes of the traced parameters. When carrying out the dynamic checks which are carried out on the working engine and also at identification of the reasons sporadic failures the oscillograph becomes absolutely irreplaceable tool.

Some oscillographs allow to keep oscillograms in the built-in module of memory with the subsequent conclusion of results to the press or their transfer to the carrier of the personal computer already in stationary conditions.

The oscillograph allows to observe periodic signals and to measure tension, frequency, width (duration) of rectangular impulses, and also levels of slowly changing tension.

The oscillograph can be used for:

  • Identifications of failures of unstable character.
  • Checks of results of the made corrections.
  • Activity control a lambda probe of a control system of the engine equipped with the catalytic converter.
  • The analysis of the signals developed a lambda probe which deviation of parameters from norm is unconditional the evidence of violation of serviceability of functioning of a control system in general, - on the other hand, correctness of a form of the impulses which are given out a lambda probe can serve as a reliable guarantee of lack of violations in a control system.

Reliability and simplicity of operation of modern oscillographs do not demand any special special knowledge and experience from the operator. Interpretation of the received information can be easily made by elementary visual comparison of the oscillograms removed during check with brought below typical for various sensors and actuation mechanisms of automobile control systems of temporary dependences.

Parameters of periodic signals

Everyone, removed by means of an oscillograph signal, can be described by means of the following key parameters:

  • Amplitude: A difference of the maximum and minimum tension (In) a signal within the period;
  • Period: Duration of a cycle of a signal (ms)
  • Frequency: Number of cycles per second (Hz);
  • Width: Duration of a rectangular impulse (ms, microsec);
  • Porosity: The repetition period relation to width (In foreign terminology the return is applied porosity the parameter called by a running cycle, expressed in %);
  • Signal form: Sequence of rectangular impulses, single emissions, sinusoid, sawtooth impulses, etc.

Usually characteristics of the faulty device strongly differ from reference that allows the operator easily and quickly visually to reveal the refused component.

Signals of a direct current - only signal tension is analyzed.

Signals of this sort are developed by the devices given on illustrations below.

Sensor of temperature of cooling liquid of the engine (ECT)

The sensor of temperature of the soaked-up air (IAT)

Sensor of provision of a butterfly valve (TPS)

Warmed up a lambda probe

Measuring instrument of a volume expense of a stream of air (VAF)

Measuring instrument of mass of air (MAF)

Signals of alternating current - are analyzed amplitude, frequency and a form of a signal.

Sensor of a detonation (KS)

Inductive sensor of turns of the engine

Frequency-modulated signals - are analyzed amplitude, frequency, a form of a signal and width of periodic impulses. Sources of similar signals are the devices given on illustrations below.

Inductive sensor of provision of a cranked shaft (CKP)

Inductive sensor of provision of a camshaft (CMP)

Inductive sensor of speed of the movement of the car (VSS)

The sensors of turns and the provision of shaft working at effect of the Hall

Optical sensors of turns and provision of shaft

Digital sensors of thermometric measurement of mass of air (MAF) and absolute pressure in the inlet pipeline (MAP)

The signals modulated on width of an impulse (ShIM) - are analyzed amplitude, frequency, a form of a signal and porosity of periodic impulses. Sources of similar signals are the devices given on illustrations below.

Injectors

Devices of stabilization of turns of idling (IAC)

Primary winding of the coil of ignition

Electromagnetic valve of a purge of a coal adsorber (EVAP)

Valves of system of recirculation of the fulfilled gases (EGR)

The form of the signal which is given out by an oscillograph depends on a set of various factors and can change considerably. In a look told before starting replacement of the suspected component in case of discrepancy of a form of the removed diagnostic signal with the reference oscillogram, it is necessary to analyse carefully received result.

Tension

Digital signal

Analog signal

Zero level of a reference signal cannot be considered as absolute basic value, - "zero" real signal, depending on concrete parameters of the checked chain, it can be shifted rather reference (see. A digital signal [1]) within a certain admissible range (see. Digital signal [2] and Analog signal [1]).

Full amplitude of a signal depends on supply voltage of the checked contour and also can vary rather reference value in certain limits (see. Digital signal [3] and Analog signal [2]).

In chains of a direct current amplitude of a signal is limited to supply voltage. It is p