GF07.10-P-1020OGG on-Board Diagnosis, Function

GF07.10-P-1020OGG On-Board Diagnosis, Function
- as of model year 09

Function requirements of On-Board Diagnose (OBD), general points
^ Circuit. 87 ON (engine control ON)

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:
- Monitors emission-related components and systems while driving
- Determining and storing malfunctions
- Displaying malfunctions by a warning lamp (CHECK ENGINE indicator lamp (A1e26) (for code (494) USA version) and engine diagnosis indicator lamp (A1e58) (except code (494) USA version)
- Determined errors are transmitted via a uniform interface (diagnostic data link connector (X11/4)) to a diagnostic unit (e.g. Diagnosis Assistance System (DAS))

The follow objectives are monitored by the OBD:
- Ensure permanently low exhaust emissions
- Protect components at risk (such as e.g. a catalytic converter) against backfires

The following components and systems are monitored:
- Intake air path
- Fuel system
- Preheating plant
- Exhaust gas recirculation
- Smooth running control
- O2 sensor
- O2 sensor heater
- Diesel particulate filter with code (474) Particulate filter by the DPF pressure differential sensor for OBD (B28/16) with code (U42) BlueTEC (SCR) diesel exhaust treatment and with code (494) USA version
- AdBlue(R) system with code (U42) BlueTEC (SCR) diesel exhaust treatment
- Intake port shutoff (EKAS) by the left intake port shutoff end position sensor (B96/1) and left intake port shutoff end position sensor (B96/2) with code (U42) BlueTEC (SCR) diesel exhaust treatment and with code (494) USA version
- Cooling system (for code (494) USA version)
- Other emission-relevant components or such components the malfunction of which prevents the diagnosis of another component

On-board diagnosis function sequence (OBD)
The OBD is described in the following items:
^ Function sequence: fault detection
^ Function sequence: test procedure
^ Function sequence: cyclic monitoring
^ Function sequence: continuous monitoring
^ Function sequence: readiness code
^ Function sequence: error storage
^ Function sequence: avoiding consequential faults
^ Function sequence: saving the fault freeze frame data
^ Function sequence: fault message
^ Function sequence: read out fault memory
^ Function sequence: error cancellation

Function sequence: fault detection
The CDI control unit checks its input and output signals for plausibility and detects possible faults.

The faults and their storage are differentiated between as follows:
- Fault permanently present
- Loose contact which occurred during a drive

The following faults are recognized in their frequency and period:
- Signals above or below the limit value (for example, short circuit, open circuit, sensor malfunction)
- Illogical combination of various signals
- Closed loop to the lower or upper limit of the regulation interval
- Faults in function chains (faulty test runs, e.g. for the smooth running control)
- Fault messages via the CAN data buses

Function sequence: test procedure
For test procedures on differentiates between component checking and the function chain test.

Component checking
The component checking is direct checking of a component. It includes:
- Monitoring of the power supply and electric circuits
- Comparison of the sensor signals with other sensor signals and stored comparative values

The following three test results can occur:
- Signal present (test passed)
- Signal not present (fault)
- Signal present, but implausible (fault)

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 from cause and effect. The CDI control unit actuates one or more components (cause) and evaluates the resulting sensor signals (effect). In the process the CD 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:
- Smooth running control
- Exhaust gas recirculation
- O2 sensor heater

Function sequence: 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:
- Fuel system
- Exhaust gas recirculation
- Smooth running control
- O2 sensor
- O2 sensor heater
- Regeneration

Function sequence: continuous monitoring
Continuous monitoring means constant monitoring of the engine start up to "ignition OFF".

The following components and systems are monitored continuously:
- Intake air path
- Preheating plant
- Particulate filter
- AdBlue(R) system
- Crankcase ventilation
- Cooling system
- All other emission-relevant components

Function sequence: readiness code
In order to obtain a statement about the lack of faults in cyclically monitored components and systems when reading out the fault memory they must be ready to test.

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. The readiness to test is determined at least once per driving cycle and sets the readiness code for a given readiness to test. 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 for setting the readiness code is not significant. This means that it is also set of a fault in the system or the components is established.

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

- Fuel system
- Exhaust gas recirculation
- Smooth running control
- O2 sensor
- O2 sensor heater

If there is no readiness to test for individual systems or components then this can be created using the diagnostic unit.

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

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

Function sequence: error storage
Exhaust gas-relevant faults from the current and previous driving cycle, which have just been determined, are buffered in the OBD until they are confirmed (occurrence in two driving cycles) in the form of a fault code, the so-called DTC (Diagnostic Trouble Code).
If an established fault occurs in two driving cycles one after the other, the fault code is stored in the CDI control unit fault memory after ending the second driving cycle.

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 while driving.

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

Function sequence: saving the fault freeze frame data
The faults which arose and the operating conditions, the so-called fault freeze frame data are stored.
If the fault occurs a second time then also this fault freeze frame data is stored. If the fault continues to occur then the last stored fault freeze frame data is updated. So the fault freeze frame data from the first and last occurrence of a fault can be read out.

Fault freeze frame data are:
- Vehicle speed
- Engine speed
- Coolant temperature
- Intake air temperature
- Boost air temperature
- Charge air pressure
- Supply voltage
- Engine load status
- Adaptation value for injection regulation

Function sequence: fault message
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: 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: error cancellation
Stored faults are only deleted 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.