Automotive electronics - What you need to know!

General points The knock sensor is on the outside of the engine block. It is used to record knocking sounds in the engine during all operating states in order to avoid engine damage. Function The knock sensor "monitors" the structure-borne vibrations on the engine block and transforms these into electrical voltage signals. These are filtered and evaluated in the control unit. The knock signal is assigned to the respective cylinder. If knocking occurs, the ignition signal for the respective cylinder is retarded as far as necessary until knocking combustion ceases.  Effects of failure A sensor can become noticeable in different ways through the fault recognition of the control unit and the resulting emergency running strategy. Frequent fault symptoms are: ■ Engine warning light comes on ■ fault code is stored ■ Reduced engine performance ■ Increased fuel consumption There can be a number of reasons for sensor failure: ■ Internal short-circuits ■ Interrupted c...

General points Wheel speed sensors are located near wheel hubs or differentials and are used to determine the speed of the outer wheel rim. They are used in ABS, ASR and GPS systems. If the systems are combined the antiblocking system provides the wheel rim speeds via data cables to the other systems. There are Hall-type sensors and inductive sensors. Before testing, it is essential to find out which type of sensor is involved (technical data, parts catalogue). Function The rotary movement of the sensor ring mounted on the drive shafts causes changes in the magnetic field in the sensor. The resulting signals are sent to the control unit and evaluated. In the case of the ABS system, the control unit determines the speed of the wheel rim which is used to determine the wheel slip, thus achieving an optimum braking effect without the wheels locking.  Effects of failure When one of the wheel speed sensors fails, the following system features are noticeable:  ■ ...

General points Transmission sensors record the gear speed. This is required by the control unit to regulate the transmission pressure during gear shifting and to decide when to switch to which gear. Function There are two types of transmission sensor designs: Hall-type sensors and inductive sensors. The rotary movement of the gear rim affects a change in the magnetic field which changes the voltage. The transmission sensor sends these voltage signals to the control unit. Effects of failure A faulty transmission sensor can become noticeable as follows:  ■ Failure of the transmission control, control unit switches to limp-home programme  ■ Engine warning light comes on  Causes of failure can be:  ■ Internal short-circuits  ■ Interrupted cables  ■ Cable short-circuits  ■ Mechanical damage to the sensor wheel  ■ Soiling through metal abrasion The following test steps should be taken into account during troublesh...

General points The coolant temperature sensor is used by the fuel induction system to record the engine operating temperature. The control unit adapts the injection time and the ignition angle to the operating conditions depending on the sensor information. The sensor is a temperature sensor with negative temperature coefficient: As temperature increases, internal resistance decreases. Function  The resistance of the temperature sensor changes depending on the coolant temperature. As the temperature increases the resistance decreases and with it the voltage at the sensor. The control unit evaluates these voltage values, since they are in direct relation to the coolant temperature (low temperatures result in high voltage values at the sensor and high temperatures in low voltage values). Effects of failure A faulty coolant temperature sensor can become noticeable in different ways through the fault recognition of the control unit and the resulting emergency runnin...

General points The intake air temperature sensor determines the temperature in the intake pipe and sends the voltage signals produced by the effect of temperature to the control unit. This evaluates the signals and influences the fuel induction and the ignition angle. Function The resistance of the temperature sensor changes depending on the intake air temperature. As the temperature increases the resistance decreases – and with it the voltage at the sensor. The control unit evaluates these voltage values, since they are in direct relation to the intake air temperature (low temperatures result in high voltage values at the sensor and high temperatures in low voltage values).  Effects of failure A faulty intake air temperature sensor can become noticeable in different ways through the fault recognition of the control unit and the resulting limp-home running strategy. Frequent fault symptoms are:  ■ Storing of a fault code and possible lighting up of the en...

To make the subject of oxygen sensors more easily understood and simplify testing in day-to-day garage work, we would like to present the function and the different testing possibilities with the oxygen sensor in this issue. Usually, the function of the oxygen sensor is tested during the routine exhaust emissions test. Since it is subject to a certain amount of wear, however, it should be checked for perfect function regularly (approx. every 18.750 miles ) – within the context of a regular service, for example. What is the oxygen sensor for?  As a result of more stringent laws governing the reduction of exhaust emissions from motor vehicles, exhaust gas treatment techniques have also been improved. Optimum combustion is necessary to guarantee an optimum conversion rate of the catalytic converter. This is achieved when the air/fuel mixture is composed of 14.7 kg of air to 1 kg of fuel (stoichiometric mixture). This optimum mixture is described by the Greek letter (lambda). Lam...

General points The task of crankshaft sensors is to determine the speed and position of the crankshaft. They are usually installed on a gear rim near the flywheel. There are two types available: inductive sensors and Hall-type sensors. Before carrying out crankshaft sensor tests it is vital to determine what type of sensor is involved. How it works The rotary movement of the gear rim affects changes in the magnetic field. The different voltage signals produced by the magnetic fields are sent to the control unit. The control unit uses the signals to calculate the speed and position of the crankshaft in order to receive important basic data for fuel injection and ignition timing Effects of failure The following fault symptoms could be indications of crankshaft sensor failure: ■ Engine misses ■ Engine comes to a standstill ■ A fault code is stored Causes of failure can be: ■ Internal short-circuits ■ Interrupted cables ■ Cable short-circuit ■ Mechanical damage to the ...