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On-Board-Diagnosis 2
| Nr. | Sensors | Nr. | Actuators |
| 1 | Lambda oxygen sensor pre-catalyst | 17 | Fuel pump relay |
| 2 | Heating Lambda I | 18 | Canister-purge valve |
| 3 | Lambda oxygen sensor after-catalyst | 19 | Camshaft adjustment |
| 4 | Heating Lambda II | 20 | Injector 1 | | 5 | Temperature coolant | 21 | Injector 2 |
| 6 | Temperature intake air | 22 | Injector 3 |
| 7 | Switch clutch pedal | 23 | Injector 4 |
| 8 | Switch brake pedal | 24 | Throttle valve servo motor |
| 9 | Potentiometer exhaust gas recirculation | 25 | Valve exhaust gas recirculation |
| 10 | Fuel supply pressure | 26 | Governor fuel pressure |
| 11 | Knock sensor | 27 | Output stage/ignition coil
cylinder 1 |
| 12 | Hall-effect pulse generator camshaft | 28 | Output stage/ignition coil
cylinder 2 |
| 13 | Speed sensor crankshaft | 29 | Output stage/ignition coil
cylinder 3 |
| 14 | Sensor for inlet manifold pressure | 30 | Output stage/ignition coil
cylinder 4 |
| 15 | Accelerator pedal | | |
| 16 | Angle transducer throttle valve | | |
Function
Since 1998 there is an EU regulation which prescribes a continuous examination and fault indication or storage during operation of all functional elements relevant for the exhaust gas. In addition, emergency run
qualities should help to avoid complete breakdowns and further damages. It is in force since 2000 for petrol engines and 2004 for diesel engines. Everything is
standardised:- the check light,- the plug-in connector,- the data transmission. Even the number of miles will be saved, completed after the first occurrence of an emission-related defect and the consequent
illumination of the Mal
function Indication Lamp.
How it works
The wiring diagram shows the most important components for an OBD-supervised petrol engine system. This starts with the insertion of the broadband
lambda oxygen sensor in
front of the catalytic converter. After it has been implemented, the Lambda value can be determined and its alterations can be observed within milliseconds. With it a diagnosis of the combustion per cylinder is
possible. The sensors in the flywheel also allow to draw conclusions on the circularity of the engine and the performance of single cylinders. However,
it is important that
beforehand a learning process has been completed, meaning enough time for the control device to rule out all additional influences as for example jerking during the initial drive.
Controlling the exhaust gas recirculation, the activated carbon system and the secondary air blow is made more exact by the improved observation data of the Lambda sensor. Moreover the processes are similar. In
certain time intervals the valves in question are opened and the alteration of the Lambda value is observed. If the expected change does not come about, the process is repeated after some time. Repeated deviations
from the preset control device values leads to an error message with further consequences.
From the above it should be obvious why a simple error message read out is not sufficient as exhaust emission test for vehicles featuring OBD. Since these could have been deleted shortly before. Therefore, all
systems must be looked at, without giving any attention to old problems. These test runs are programmed by the manufacturer in such a way that they do not take too much time in the workshop. It is not necessary to
actually take the car for a ride.
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