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

Engine 274 in model 907 

Block diagram 

Function requirement for European On-Board Diagnosis (EOBD), general points 

• Circuit 87M (Engine management ON)

European OBD (OBD), general 

The EOBD system is integrated in the ME-SFI [ME] control unit (N3/36) and constantly monitors all emissions-relevant vehicle components and systems.

The EOBD has the following tasks:

• Monitor emissions-relevant assembly parts and systems while driving.
• Establish malfunctions and save them.
• Display malfunctions using symbols in the IC (A1).
• Transmit errors via a uniform interface (diagnostic connection (X11/4)) to a diagnostic device (e.g. XENTRY Diagnostics).

EOBD pursues the follow objectives:

• Achieving permanently low exhaust emissions.
• Protecting at risk components (e. g. catalytic converters) against backfires.

The following assembly parts and systems are monitored:

• Lambda sensor downstream of the catalytic converter (G3/21)
• Oxygen sensor upstream of catalytic converter (G8/6)
• Efficiency of catalytic converters (catalytic converter function)
• Catalytic converter heating
• Purge control
• Smooth running analysis (recognition of combustion misfires)
• Other emissions-relevant components or such components a malfunction of which prevents diagnosis of other components.

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 ME-SFI control unit checks itself and its input and output signals for plausibility and recognizes possible faults.

• Comparison of sensor signals with other sensor signals and stored comparative values

The following three test results can occur:

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 (e.g. lambda control) at the lower or upper limit of the controlling interval
• faults in function chains (faulty test runs, e.g. for purging)
• 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
• 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 ME-SFI control unit actuates one or more assembly parts (cause) and evaluates the resulting sensor signals (effect). Here the ME-SFI control unit compares the sensor signals with stored comparative values and thus recognizes the trouble-free or not trouble-free function of assembly parts and systems.

The following are monitored over function chain tests:

• Selfadaptation of mixture formation
• Smooth running analysis (recognition of combustion misfires)
• Catalytic converter function
• Oxygen sensors (aging and controlling)
• Oxygen sensor heater
• Purge control

Function sequence for cyclic monitoring 

Cyclic monitoring takes place for components and systems which are not permanently active. Purging takes place, for example only for driving operations in the partial-load range and can only then be monitored in this operating phase.

The following components and systems are monitored cyclically:

• Catalytic converter function
• Catalytic converter heating
• Oxygen sensors (aging and controlling)
• 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:

• Smooth running analysis (recognition of combustion misfires)
• Selfadaptation of mixture formation
• automatic transmission (fitted with its own EOBD with a fault memory)
• 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 an assembly parts 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 assembly parts or the system is active.

The checking readiness is determined at least once per driving cycle and the readiness code is set for a given checking readiness. To set the readiness code, it suffices that the vehicle has checked all components that belong to 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 assembly parts and systems if their testing has occurred:

• Catalytic converter function
• Catalytic converter heating
• Oxygen sensors (aging and controlling)
• 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 DTCs.

Function sequence for error saving 

Emissions-relevant faults from the current and previous driving cycle that have just been determined are temporarily stored in the EOBD until their confirmation (occurrence in two successive driving cycles) in the form of a fault code, the so-called "Diagnostic Trouble Code". If an established fault occurs in two driving cycles once after the other, the DTC is stored in the fault memory of the ME-SFI control unit after ending the second driving cycle.

Driving cycle

A driving cycle consists of the engine start, vehicle trip and engine OFF, whereby an increase in the coolant temperature by at least 22 °C to at least 70 °C must take place.

Function sequence for avoiding consequential faults 

If a faulty signal is detected and saved, all tests are canceled in which this signal is required as a comparative value (so-called cross-locking).

Saving of consequential faults is thereby prevented.

Function sequence for saving the fault freeze frame data 

In addition to the occurred fault, the operating parameters and conditions - the so-called fault 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 manifold pressure
• Charge air temperature
• Supply voltage
• Engine throttle condition
• Mixture formation adaptation value
• Status of the lambda control

Function sequence for fault message 

The engine diagnosis indicator lamp (A1e58) in the instrument cluster is actuated by the ME-SFI [ME] control unit via the drive CAN (CAN C), powertrain control unit (N127), suspension FlexRay (Flex E), electronic ignition lock control unit (EZS) (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 ME-SFI [ME] control unit is connected via the drive CAN, powertrain control unit, suspension FlexRay, EZS control unit and the diagnostics CAN (CAN D) to the diagnostics connection.

Stored DTCs and their fault freeze frame data as well as the readiness codes can be read out using a commercially available diagnostic equipment or XD for "ignition ON" or for a running engine over the diagnostic connector.

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.

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