EUROPEAN OBD, Function - GF07.10-D-1021TSC

Engine 642.8 in model 907 

Block diagram 

Function requirements for European On-Board Diagnosis, general 

• Circuit 87M ON (Engine management ON)

European OBD (OBD), general 

The second generation on-board diagnostics system, the European On-Board Diagnostics (EOBD), constantly monitors all emissions-relevant components and systems of the vehicle. The EOBD system is integrated in the CDI control unit (N3/28) and has the following tasks:

• Monitor emissions-relevant assembly parts and systems while driving.
• Establish malfunctions and save them.
• Display of malfunctions via the engine diagnosis indicator lamp (A1e58).
• Transmit detected errors via a uniform interface (diagnostics connection) to a diagnostic device (e.g. XENTRY Diagnostics).

EOBD pursues the follow objectives:

• Achieving permanently low exhaust emissions.
• Protect assembly parts at risk (e.g. the catalytic converter).

The following assembly parts and systems are monitored:

• Intake air path
• Fuel system
• Glow system
• Exhaust gas recirculation
• Smooth running control
• Oxygen sensor
• Oxygen sensor heater
• Diesel particulate filter
• AdBlue® system
• Crankcase ventilation system
• Cooling system
• Other emission-relevant components or components whose malfunctioning prevents the diagnosis of another component.

Function sequence for European OBD 

The EOBD is described in the following steps:

• Function sequence for fault detection
• Function sequence for test procedure
• Function sequence for cyclic monitoring
• Function sequence for continuous monitoring
• Function sequence for readiness code
• Function sequence for error saving
• Function sequence for avoiding consequential faults
• Function sequence for saving the fault freeze frame data
• Function sequence for fault message
• Function sequence for reading out the fault memory.
• Function sequence for fault clearing

Function sequence for fault detection 

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

The faults and their storage are differentiated between as follows:

• The fault is always there
• Loose contact which occurs during a drive.

The following faults are recognized according to their frequency and duration:

• Signals above or below the limit value (for example, short circuit, open circuit, defective sensor)
• An illogical combination of various signals
• Closed-loop control circuit at lower or upper limit of the regulation interval
• Malfunctions in function chains (faulty test processes, e.g. for the smooth running control)
• Fault messages via the CAN buses

Function sequence for test procedure 

A differentiation is made during the test procedure between component testing and function chain testing.

Assembly part checking 

The component checking is direct checking of a assembly part. It includes:

• Monitoring the power supply and electric circuit
• Comparison of sensor signals with other sensor signals and stored comparative values

The following three test results can occur:

• Signal present (checking passed)
• Signal not present (a fault)
• Signal present, but implausible (a fault)

Function chain test 

The function chain test is indirect checking of the effect of controlled change. Here individual assembly parts and systems are checked which cannot be checked over a component checking. The function chain is a controlled procedure of cause and effect.

The CDI control unit controls one or more assembly parts (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 assembly parts and systems.

The following are monitored over function chain tests:

• Smooth running control
• Exhaust gas recirculation
• Oxygen sensor heater

Function sequence for cyclic monitoring 

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

The following components and systems are monitored cyclically:

• Fuel system
• Exhaust gas recirculation
• Smooth running control
• Oxygen sensor
• Oxygen sensor heater
• Purge control

Function sequence for continuous monitoring 

Continuous monitoring means continuous monitoring from engine start to "ignition OFF".

The following components and systems are monitored continuously:

• Intake air path
• Glow system
• Diesel particulate filter
• AdBlue® system
• Crankcase ventilation system
• Cooling system
• All other emissions-relevant components

Function sequence for readiness code 

In order to obtain a statement about freedom from faults of cyclically monitored components and systems during read out of the fault memory, there must be test readiness for this.

The test readiness of a component or a system is shown using the "readiness code". The readiness code allows recognition of whether checks for malfunction detection have run at least once and therefore the component or the system is active.

The test readiness is determined at least once per driving cycle and the "readiness code" is set for a given test readiness. To set the "readiness code", it is sufficient if the vehicle has checked all components associated with a system at least once.

The test result for setting the "readiness code" is not important. This means that it will also be set if a fault is found in the systems or the component.

The "readiness code" is set for the following components or systems once they have been tested:

• Fuel system
• Exhaust gas recirculation
• Smooth running control
• Oxygen sensor
• Oxygen sensor heater
• Purge control

If the test readiness of individual systems or assembly parts is not given then these can be created using the diagnostic unit. To do this the function chain sequence is started manually over a menu item of the software.

All "readiness codes" are reset automatically when deleting fault codes.

Function sequence for error saving 

Emissions-relevant faults from the current and previous driving cycle that have just been detected are stored in the interim until confirmation (occurrence in two driving cycles one after the other) in the form of a fault code, the so-called "Diagnostic Trouble Code", in the EOBD.

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.

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 to at least 70 °C must occur during travel.

Function sequence for avoiding consequential faults 

If a faulty signal is recognized and stored all tests are broken off for which this signal is need as a comparative value (so-called transverse locking). Saving of consequential faults is thereby prevented.

Function sequence for saving the fault freeze frame data 

In addition to the fault that occurred, the operating conditions, the so-called fault freeze frame data ("Freeze Frame Data") are saved. If the fault occurs a second time then also these fault freeze frame data are stored. If the fault continues to occur then the last stored fault freeze frame data is updated. The fault freeze frame data can be read out for the first and last occurrence of a fault.

Fault freeze frame data include:

• Vehicle speed
• Engine speed
• Coolant temperature

• Intake air temperature
• Charge air temperature and boost pressure
• Supply voltage
• Engine throttle condition
• Adaptation value for injection regulation

Function sequence for fault message 

The engine diagnosis indicator lamp (A1e58) in the instrument cluster is actuated by the CDI control unit via the drive CAN (CAN C), powertrain control unit (N127), suspension FlexRay (Flex E), electronic ignition lock (EZS) control unit (N73/8), and the user interface CAN (CAN HMI).

If a fault occurs in two driving cycles, one after the other, the indicator lamp engine diagnosis lights up. In the case of catalytic converter damage caused by ignition misfires the engine diagnosis indicator lamp flashes for as long as the ignition misfires occur and then lights up permanently during the whole (remaining) driving cycle.

The fault message via the engine diagnosis indicator lamp disappears automatically after 3 successive trouble-free driving cycles.

Function sequence for reading out the fault memory 

The CDI control unit is connected to the diagnostics connection via the drive CAN, powertrain control unit, suspension FlexRay, EZS control unit and the diagnostics CAN. Stored fault codes and their fault freeze frame data and the "readiness codes" can be read out using a commercially available diagnostic device or XENTRY Diagnostics for "ignition ON" or for a running engine via the diagnostics connection.

Function sequence for fault clearing 

Saved faults are only automatically deleted from the fault memory after 40 successive trouble-free driving cycles. They can, however, also be cleared (after repair work has been done) using commercially available diagnostic equipment or Xentry Diagnostics.

Electrical function schematic for electrical European On-board Diagnosis	PE07.10-D-2725-97TSC
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSC