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

Engine 274.9 in model 172.4 

as of model year 2017 

Engine 276.8 in model 172.4 

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

• Circuit 87M (Engine management ON)

European OBD (OBD), general 

A second generation On-Board Diagnosis system is used (OBD II)). 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 of malfunctions via the engine diagnosis indicator lamp (A1e58)
• 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 assembly parts at risk (such as catalytic converters) against backfires

The following assembly parts and systems are monitored:

• Catalytic converter heating
• Smooth running analysis (recognition of combustion misfires)
• Oxygen sensor downstream of catalytic converter (G3/1) and oxygen sensor upstream of catalytic converter (G3/2) (engine 274.9)
• Remove left oxygen sensor upstream of CAT (G3/3) or right oxygen sensor upstream of CAT (G3/4) or left oxygen sensor downstream of CAT (G3/5) or right oxygen sensor downstream of CAT (G3/6) (engine 276.8)
• Purge control
• Other emissions-relevant components or such components a malfunction of which prevents diagnosis of other components
• Efficiency of the CAT (catalytic converter function)

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 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 chain (faulty test sequences, 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 checking 

The assembly part 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.

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 [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-adjustment of mixture formation
• Smooth running analysis (recognition of combustion misfires)
• Catalytic converter function
• Oxygen sensors (aging and controlling)
• Oxygen sensor heater
• Purging

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
• Purging

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-adjustment of mixture formation

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 part 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 part 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 components and systems if their testing has occurred:

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

If the test readiness of individual systems or components 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 [ME] control unit after ending the second driving cycle.

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.

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 lambda control

Function sequence for fault message 

The engine diagnosis indicator lamp in the IC (A1) is actuated by the ME-SFI [ME] control unit via chassis CAN 1 (CAN E1), front SAM control unit with fuse and relay module (N10/1) and chassis CAN 2 (CAN E2).

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 networked via chassis CAN 1, the front SAM control unit with fuse and relay module and the diagnostic CAN (CAN D) with the diagnostic connector. 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.

	Electrical function schematic for electrical European On-board Diagnosis		PE07.10-P-2725-97TAI
	Overview of system components for gasoline injection and ignition system with direct injection	Engine 276.8 in model 172.4	GF07.70-P-9998MNC
		Engine 274.9 in model 172.4 as of model year 2017	GF07.70-P-9998MRE