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On-Board Diagnosis, Function - GF07.10-D-1020HD

ENGINES 651.955/956/957 in MODEL 906 

with CODE (XZ1) Model generation 1 

with CODE (MZ0) Blue EFFICIENCY 

Function requirement 

General 

The OBD with appropriate adaptations for the European market is integrated into the CDI control unit (N3/28) and constantly monitors all emissions-relevant components and systems on the vehicle.

The OBD has the following tasks:

Use of OBD pursues the following objectives:

Amongst others the following components and systems are monitored:

Function sequence 

The OBD is described in the following steps:

Function sequence for fault detection 

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

Malfunctions and the way they are stored are classified 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 faulty 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. Purging takes place, for example only for driving operation in partial-load range and can only then be monitored in this operating phase.

The following components and systems are monitored cyclically:

Function sequence for continuous monitoring 

Continuous monitoring means constant monitoring of "circuit 15 ON" up to "circuit 15 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 readiness to test of a component or a system is shown by the readiness code. Through the readiness code it is possible to recognize whether checks for indication of disturbance have run at least once and therefore 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 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 a component is found.

The readiness code is set for the following components and system if their testing has occurred:

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

Emissions-relevant faults from the current and the previous driving cycle, which have just been detected, are stored in the interim until confirmation (occurrence in 2 driving cycles one after the other) in the form of an DTC in the OBD.

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 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.

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 (interlock). This prevents consequential faults from being stored.

Function sequence for saving the fault freeze frame data 

The faults which arose as well as the operating parameters or conditions, the so-called fault freeze frame data, are stored. 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.

The fault freeze frame data includes:

Function sequence for fault display 

The EOBD indicator lamp in the IC (A1) is actuated by the CDI control unit via the interior CAN (CAN B).

If a malfunction occurs in two consecutive driving cycles, the EOBD indicator lamp lights up.

In the case of catalytic converter damage caused by ignition misfires the EOBD indicator lamp flashes for as long as the ignition misfires occur and then lights up permanently during the whole (remaining) driving cycle.

Fault indication by means of the EOBD indicator lamp ceases automatically after 3 consecutive trouble-free driving cycles.

Function sequence for reading out fault memory 

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 DAS for "circuit 15 ON" or for "circuit 61 ON" over the 16-pin diagnostic socket.

Function sequence for erasing faults 

The system will automatically erase any stored malfunctions from the fault memory only after 40 consecutive trouble-free driving cycles have occurred. They can, however, also be deleted after repair work has been done using a commercially available diagnostic unit or the DAS.

CDI control unit, component description N3/28 GF07.16-D-6000HD 
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