Mercedes S-Class
+ Mercedes-Benz cars of the class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Cooling systems, heating
+ Power supply system and release
- Engine electric equipment
- Systems of ignition and engine management - the general information
Checks of a control system of ignition and injection
Search of malfunctions - the general information and preliminary checks
Check and adjustment of a corner of an advancing of ignition
Spark plugs
Self-diagnostics of systems of electronic control of OBD
Diagnostics of electronic system of the automatic air conditioner (AC)
Application of an oscillograph for observation of signals of a control system
Ignition coils - installation details
Removal, installation and adjustment of the sensor of position of the camshaft (CMP)
The distributor of ignition (M119.97 engines) - installation details
+ Systems of a charge and start
+ Gear shifting box
+ Automatic transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment
Search of malfunctions - the general information and preliminary checks
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Address also Diagnostics of malfunctionsthe Section Introductions |
The system of ignition and fuel system are the interconnected components of a control system of the engine.
General information
The system of ignition and fuel system have the general diagnostic system intended for preservation of codes of malfunctions and performing diagnostics. At malfunction emergence the control unit writes down in memory some sequence of signals (a malfunction code) which can be considered the special device subsequently (see the Section Self-diagnostics of Systems of Electronic Control of OBD).If failures in operation of the engine of the car are observed, the reason of it, most likely, can be found out, having investigated memory of the control unit. After reading of codes of malfunctions it is possible to find out what knot is faulty and to execute the corresponding checks (either the knot, or its electrical wiring).
Visual check of an electrical wiring and sockets is not enough - surely consider information which is stored in memory of the control unit.
Preliminary checks
If malfunction arose soon after service of any knot, first of all carefully check this knot and surrounding space. Perhaps, the reason is covered in carelessly installed component or unreliably attached socket.If you try to find the reason of a certain malfunction of the engine, for example falling of power, in addition to the actions given below measure a compression in cylinders. Make sure that the fuel filter and the air cleaner changed according to the ordered intervals.
Keep in mind that after reading of codes of malfunctions they need to be removed from memory of the control unit by means of the same diagnostic scanner then to eliminate malfunction.
Open a cowl and be convinced of reliability of accession of tips of wires to plugs of the accumulator and lack of corrosion on them. At detection of traces of corrosion or damages replace or clear wires. Similarly check all tires of grounding, having convinced that they provide reliable contact (the interfaced surfaces have to be absolutely pure and without corrosion traces) with a body or the engine.
After that attentively examine all visible conducting laid in a motive compartment. Be convinced of reliability of all connections. At this stage you are interested in obviously damaged wires. They can be cut or ground about the sharp or moving engine knots, for example, of a detail of a suspension bracket or a driving belt. The break of a wire can result from negligent installation of any knot. The wire can melt at contact with system of release. The wrong laying of its plaits in a motive compartment after performance of repair or service of any knot is the most probable cause of damage of conducting.
Wires can be damaged or short-circuited without damage of their isolation. In this case survey will not lead to anything. Similar damages can arise after a pulling of wires or the wrong placement of conducting in a motive compartment. If you consider that similar damage is possible, check a wire, following the sequence stated below.
The damaged wire can be repaired, having sealed a piece of a new wire in a gap. The soldering is necessary for receiving reliable contact. Isolation can be restored enough an insulating tape or a thermoshrinkable tube. If damages are considerable and t