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On-board diagnosis, function - GF07.10-P-1020OGG

ENGINES 642.8 in MODEL 164.1 as of model year 2009/YoM 08 model refinement package 

ENGINES 642.8 in MODEL 164.8, 251.1 as of model year 2009/YoM 08 

ENGINES 642.8 in MODEL 251.0/1 as of model year 2011/YoM 10 model refinement package 

Function requirements for On-Board Diagnose (OBD), general points 

On-board Diagnosis (OBD), general 

An OBD system of the second generation is used (on-board diagnosis II (OBD II)). In Europe, the OBD II, with appropriate adaptation for the European market, is called European On-board Diagnosis (EOBD).

The OBD system is integrated in the CDI control unit (N3/9) and constantly monitors all exhaust gas relevant components and systems of the vehicle.

The OBD has the following tasks:

The follow objectives are monitored by the OBD:

The following components and systems are monitored:

Function sequence for on-board diagnosis (OBD) 

The OBD is described in the following steps:

Function sequence for fault detection 

The CDI control unit checks its input and output signals for plausibility and detects possible malfunctions.

Malfunctions and their storage are differentiated as follows:

The following malfunctions are recognized in their frequency and duration:

Function sequence for test procedure 

For test procedures one differentiates between component testing and function chain testing.

Component testing 

Component testing is direct testing of a component. It includes:

The following three test results can occur:

Function chain test 

The function chain test is indirect testing of the effect of a controlled change.

In this process individual components and systems are checked which cannot be tested by means of component testing.

The function chain is a controlled process studying cause and effect. The CDI control unit actuates one or more components (cause) and evaluates the resulting sensor signals (effect). In the process the CDI control unit compares the sensor signals with stored comparative values and thus recognizes trouble-free or not trouble-free functioning of components and systems.

The following are monitored by means of function chain tests:

Function sequence for cyclic monitoring 

Cyclic monitoring takes place for components and system which are not permanently active. Regeneration, for example, only takes place when the vehicle is being operated in the partial-load range and can therefore only be monitored during this operating phase.

The following components and systems are monitored cyclically:

Function sequence for continuous monitoring 

Continuous monitoring means constant monitoring from engine start up to "ignition OFF".

The following components and systems are monitored continuously:

Function sequence for readiness code 

In order to gain reliable information as to the trouble-free status of cyclically monitored components and systems when reading out the fault memory, these components and systems must be test ready.

The test readiness of a component or a system is shown by the readiness code. The readiness code tells you whether malfunction detection tests have been run at least once, indicating that the component or the system is active.

Test readiness is checked at least once per driving cycle. If test readiness exists, the readiness code will be set. In order to set the readiness code it is therefore sufficient if the vehicle has checked all of the components belonging to a system at least once.

The test result is not significant in setting the readiness code. This means that it is also set if a fault in the system or the component is found.

The readiness code is set for the following components and system once they have been tested:

If test readiness does not exist for individual systems or components, it can be established using the diagnostic unit.

To do this the function chain process is started manually using a menu item in the diagnostic software.

IMPORTANT All readiness codes are reset automatically when the fault code is deleted.

Function sequence for fault storage 

Exhaust gas-relevant malfunctions just found from the current and previous driving cycle are temporarily stored in the OBD until confirmed (through occurrence in two driving cycles) in the form of a fault code, also called a diagnostic trouble code or DTC.

If a found malfunction occurs in two consecutive driving cycles, the fault code is stored in the CDI control unit fault memory after the second driving cycle is completed.

IMPORTANT Driving cycle

A driving cycle consists of an engine start, vehicle journey and stopping the engine, whereby an increase in coolant temperature by at least 22°C up to at least 70°C must occur during travel.

Function sequence for avoiding consequential faults 

If a faulty signal is detected and stored, all tests where this signal is required as a reference parameter are aborted (the so-called cross locking mechanism). This prevents consequential faults from being stored.

Function sequence for saving the fault freeze frame data 

Besides the malfunctions, the operating conditions under which they occurred are also stored, the so-called fault freeze frame data.

If the malfunction occurs a second time, the associated fault freeze frame data will again be stored. If the malfunction continues to occur then the last stored fault freeze frame data will be updated. This means that the fault freeze frame data from the first and last occurrence of a malfunction can be read out.

Fault freeze frame data include:

Function sequence for fault indication 

The CHECK ENGINE indicator lamp (for code (494) USA version) or the engine diagnosis indicator lamp (except code (494) USA version) in the instrument cluster (A1) is actuated by the CDI control unit via the engine compartment-CAN (CAN C).

If a fault occurs in two driving cycle one after the other, the CHECK ENGINE indicator lamp or the engine diagnosis indicator lamp lights up.

In the case of catalytic converter damaging ignition misfires the CHECK ENGINE indicator lamp or the engine diagnosis indicator lamp lights up for as long as the ignition misfires occur and then lights up permanently in the whole (the remaining) driving cycle. The fault display over the CHECK ENGINE indicator lamp or the engine diagnosis indicator lamp goes out automatically after 3 trouble-free driving cycles occurring one after the other.

Function sequence for read out fault memory 

The CDI control unit is connected via the engine compartment CAN, the central gateway control unit (N93) and the diagnostic CAN (CAN D) with the data link connector. Stored fault codes and their fault freeze frame data as well as the readiness code can be read out using a commercially available diagnostic unit or the Diagnosis Assistance System for "ignition ON" or for a running engine via the data link connector.

Function sequence for erasing faults 

Stored malfunctions are only erased automatically from the fault memory after 40 consecutive trouble-free driving cycles. They can, however, also be deleted after repair work has been done using a commercially available diagnostic equipment or the DAS.

REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for on-board diagnosis Model 164 PE07.10-P-2720-97MAA
Model 251 PE07.10-P-2720-97RAA
  Component description for instrument cluster A1 GF54.30-P-6000GM
  Component description for CDI control unit N3/9 GF07.16-P-6000OGU 
  Component description for central gateway control unit N93 GF54.21-P-4170GM
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