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

Engine 176.9 in model 463 

as of model year 2016 up to model year 2019 

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

• Circuit 87M (Engine management ON)

The circuit relay 87M(F58kN) is switched on for circuit 15 ON.

European OBD (OBD), general 

A second generation On-Board Diagnosis system is used. In Europe, with appropriate adaptations for the European market, it is called European OBD (EOBD).

The EOBD system is integrated in the ME-SFI 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 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.
• Protect at risk components (e. g. catalytic converters) against backfires

The following assembly parts and systems are monitored:

• Remove left lambda sensor upstream of catalytic converter (G3/3) and right lambda sensor upstream of catalytic converter (G3/4)
• Remove left lambda sensor downstream of catalytic converter (G3/5) and right lambda sensor downstream of catalytic converter (G3/6)
• 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 another component.

Function sequence for European OBD 

The EOBD function comprises the following subfunctions:

• 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 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.

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.

Component testing:

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 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.

Is monitored over the function chain test:

• Self-adaptation of mixture formation
• Smooth running analysis (recognition of combustion misfires)
• Catalytic converter function
• Sensor element for left lambda sensor upstream of catalytic converter (G3/3b1) and sensor element for right lambda sensor upstream of catalytic converter (G3/4b1) (aging and control)
• Sensor element for left lambda sensor downstream of catalytic converter (G3/5b1) and sensor element for right lambda sensor downstream of catalytic converter (G3/6b1) (aging and control)
• Left lambda sensor heater upstream of catalytic converter (G3/3r1) and right lambda sensor heater upstream of catalytic converter (G3/4r1)
• Left lambda sensor heater downstream of catalytic converter (G3/5r1) and right lambda sensor heater downstream of catalytic converter (G3/6r1)
• Purge control

Function sequence for cyclic monitoring 

The cyclic monitoring takes place for components and system 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
• Sensor elements for left and right lambda sensor upstream of catalytic converter (aging and control)
• Sensor elements for left and right lambda sensor downstream of catalytic converter (aging and control)
• Left and right lambda sensor heaters upstream of catalytic converter
• Left and right lambda sensor heaters downstream of catalytic converter
• 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)
• Self-adaptation of mixture formation
• A/T (A/T is 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 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 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 assembly parts and systems if their testing has occurred:

• Catalytic converter function
• Catalytic converter heating
• Sensor elements for left and right lambda sensor upstream of catalytic converter (aging and control)
• Sensor elements for left and right lambda sensor downstream of catalytic converter (aging and control)
• Left and right lambda sensor heaters upstream of catalytic converter
• Left and right lambda sensor heaters downstream of catalytic converter
• Purge control

If the test readiness of individual systems or assembly parts is not given then these can be created using the XENTRY Diagnostics. 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 malfunctions just found from the current and previous driving cycle are temporarily stored in the EOBD until confirmed (through occurrence in two consecutive driving cycles) in the form of a fault code, also called a diagnostic trouble code or DTC.

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.

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

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 

The faults which arose as well as the operating parameters or 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 lambda control

Function sequence for fault message 

The ME-SFI control unit transmits the request to switch on the engine diagnosis indicator lamp (A1e58) via the drive CAN (CAN C), powertrain control unit (N127), suspension CAN 1 (CAN E1), electronic ignition lock control unit (N73) and interior CAN (CAN B) to the IC. 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 constantly during the whole (remaining) driving cycle. Fault message over the engine diagnosis indicator lamp ceases automatically after three consecutive trouble-free driving cycles.

Function sequence for reading out the fault memory 

The ME-SFI control unit is connected via drive CAN, powertrain control unit, suspension CAN 1, electronic ignition lock control unit (N73), and diagnostic CAN (CAN D) to the diagnostics connection. With "ignition ON" or with the engine running, stored fault codes and their fault freeze frame data as well as the readiness code can be read out using XD 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 also be cleared again after repair using XD.

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