On-Board Diagnosis, Function - GF07.10-P-1020KJ

ENGINE 281.910 in MODEL 453.0/3/4 

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

• Circuit 87 (Engine management ON)

European OBD (OBD), general 

There is a OBD system of the second generation (OBD II) being used. In Europe the OBD II, with appropriate adaptations for the European market is called European OBD (EOBD).

The EOBD system is integrated in the ME-SFI [ME] control unit (N3/10) and constantly monitors all emissions-relevant components and systems of the vehicle.

The EOBD has the following tasks:

• Monitor emissions-relevant components and systems while driving
• Establish malfunctions and save them
• Display malfunctions by means of indicator lamps in IC (A1) (for code K35 (IC with a monochrome display)) or (for code K36 (IC with a colored 8.9 cm (3.5") display))
• Transmit errors via a uniform interface (diagnostic connector (X11/4)) to a diagnostic unit (e.g. Xentry Diagnostics)

EOBD pursues the follow objectives:

• Achieving permanently low exhaust emissions
• Protect components at risk (such as catalytic converters) against backfires

The following components and systems are monitored:

• Oxygen sensor downstream of catalytic converter (G3/1)
• Oxygen sensor upstream of catalytic converter (G3/2)
• Efficiency of the CAT (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 [ME] 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 (e.g. lambda control) at the lower or upper limit of the controlling interval
• Faults in function chain (faulty test sequences, e g. for purging)
• Fault messages via interior CAN (CAN B)

Function sequence for test procedure 

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

Component checking 

The component checking is direct checking of a component. 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. Individual components and systems are checked which cannot be checked using component testing. The function chain is a controlled procedure of cause and effect. The ME-SFI [ME] control unit actuates one or more component (cause) and evaluates the resulting sensor signals (effect). Here the ME-SFI [ME] control unit compares the sensor signals with stored comparative values and thus recognizes the trouble-free or not trouble-free function of components and systems.

The following are monitored over function chain tests:

• Self adaptation 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 only takes place, for example, for driving in partial-load range and can therefore also on 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 are monitored continuously:

• Smooth running analysis (recognition of combustion misfires)
• Self adaptation of mixture formation
• Dual clutch transmission (for code (429) Dual clutch transmission) equipped with its own EOBD with 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 a component or a system is shown using the readiness code. The readiness code tells you whether fault detection tests have been run at least once, indicating that the components or the system is active.

The readiness is determined at least once per driving cycle and the readiness code is set for a given readiness. For setting the readiness code, it is sufficient if the vehicle has checked all components associated with the 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 and systems if their testing has occurred:

• Catalytic converter function
• Catalytic converter heating
• Oxygen sensors (aging and controlling)
• Oxygen sensor heater
• Purge control

All readiness codes are reset automatically when deleting DTCs.

Function sequence for error saving 

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 two driving cycles one after the other) in the form of a fault code in the EOBD.

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 [ME] control unit after ending the second driving cycle.

Driving cycle

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

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 

Further to the occurring fault the operating parameter and conditions, the so-called Fault Freeze Frame Data, are stored.

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 are, for example:

• Vehicle speed
• Engine speed
• Coolant temperature
• Boost pressure
• Charge air temperature
• Supply voltage
• Engine throttle condition
• Adaptation value of the mixture formation
• Status of the lambda control

Function sequence for fault message 

The engine diagnosis indicator lamp (A1e58) in IC (for code K35 (IC with a monochrome display)) or (for code K36 ((IC with a colored 8.9 cm (3.5") display)) is actuated by the ME-SFI [ME] control unit via the interior CAN.

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.

Fault message by means of the engine diagnosis indicator lamp goes out automatically after 3 consecutive trouble-free driving cycles.

Function sequence for reading out the fault memory 

The ME-SFI [ME] control unit is connected via the interior CAN with the diagnostic connector. 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 

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

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