European OBD, Function - GF07.10-P-1021MRS

Engine 264.9 in Model 205, 253 

Function requirements, general 

• Circuit 87M (Engine management ON)

The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10). The ME-SFI [ME] control unit then actuates the circuit 87M relay (K40/8kN). The circuit 87M relay switches the battery voltage (circuit 30) to circuit 87M. When circuit 87M is switched through to the ME-SFI [ME] control unit, it starts the Engine management.

European On-Board Diagnosis (EOBD) general points 

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

The EOBD has the following tasks:

• Monitor emissions-relevant assembly parts and systems while driving
• Establish malfunctions and save them
• Displaying malfunctions on the instrument cluster (A1)
• Data exchange via an interface (diagnostics connection (X11/4)) with a diagnostic device

EOBD pursues the follow objectives:

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

The following systems are monitored:

• Lambda control
• 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

The EOBD is described in the following steps:

• Fault detection 
• Test procedure 
• Cyclic monitoring 
• Continuous monitoring 
• Readiness code 
• Fault storage 

Fault detection 

The ME-SFI [ME] control unit checks itself and the input and output signals for plausibility.

The ME-SFI [ME] control unit differentiates between faults depending on the occurrence thereof:

• Constantly present fault
• Temporary fault (e. g. loose contact)

The ME-SFI [ME] control unit differentiates between the following type of faults:

• Measurement values that lie above or below a limit value (e. g. short circuit, open circuit, defective sensor)
• Illogical combination of different measurement values or 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 CAN

Test procedure 

One differentiates for test procedures between component checking and function chain test.

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.

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 assembly parts (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 assembly parts 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
• Purge control
• Oxygen sensor downstream of catalytic converter (G3/1)
  • Oxygen sensor sensor element downstream of catalytic converter (G3/1b1)
  • Oxygen sensor heater downstream of catalytic converter (G3/1r1)
• Oxygen sensor upstream of catalytic converter (G3/2)
  • Oxygen sensor sensor element upstream of catalytic converter (G3/2b1)
  • Oxygen sensor heater upstream of catalytic converter (G3/2r1)

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 systems and components are monitored cyclically:

• Catalytic converter function
• Catalytic converter heating
• Purge control
• Oxygen sensor sensor elements
• Oxygen sensor heaters

Continuous monitoring 

A continuous monitoring means constant monitoring from Engine start to ignition OFF.

The following systems and components are monitored continuously:

• Smooth running analysis (recognition of combustion misfires)
• Self-Adaptation of mixture formation
• A/T (A/T is fitted with its own EOBD with a fault memory)
• All other emissions-relevant components

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 system or component is shown using the readiness code. The readiness code shows whether checks for malfunction detection have run at least once and therefore the system or the component is active.

The readiness is determined at least once per driving cycle and the readiness code is set for a given readiness. To set the readiness code it is sufficient if the vehicle has checked all components belonging 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
• Purge control
• Oxygen sensor sensor elements
• Oxygen sensor heaters

If individual systems or components are not ready for testing, readiness can be established using a diagnostic tester. 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.

Fault storage 

Emissions-relevant faults from the current and previous driving cycle are temporarily stored in the EOBD in the form of a fault code, the so-called Diagnostic Trouble Code until they have been confirmed (occurrence in two successive driving cycles).

If a fault occurs in two successive driving cycles, the fault code is stored in the fault memory of the ME-SFI [ME] control unit at the end of the second 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.

If a faulty signal is detected and a fault has been stored, all tests where this signal is required as a reference parameter are aborted (the so-called cross-locking). Saving of consequential faults is thereby prevented.

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 include:

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

If a fault occurs in two successive driving cycles, the Engine diagnosis display in the instrument cluster lights up. In the case of misfires that cause damage to the catalytic converters, the Engine diagnosis display flashes for as long as the misfires occur and subsequently lights up/appears permanently in the entire (remaining) driving cycle. The fault message via the Engine diagnosis display disappears independently after 3 successive fault-free driving cycles. The ME-SFI [ME] control unit transmits the request to actuate the Engine diagnosis display via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster.

Stored fault codes, their freeze frame data and the readiness codes can be read out using the diagnostic tester with circuit 15 On or with the Engine running.

Stored faults are only deleted automatically from the fault memory after 40 successive trouble-free driving cycles have taken place. However, they can also be deleted after a repair using the diagnostic tester.

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