On-board diagnosis, function - GF07.10-P-1020MMQ

ENGINE 276.8 in MODEL 207, 212 as of model year 2014 

ENGINE 276.8 in MODEL 218 as of model year 2015 

ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 as of model year 2014 

Function requirements for European OBD (OBD), general 

• Circuit 87M (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 OBD system is integrated into the ME-SFI [ME] control unit (N3/10) and constantly monitors all emissions-relevant components and systems on the vehicle.

The OBD has the following tasks:

• Monitor emissions-relevant components and systems while driving
• Establish malfunctions and save them
• Indicate malfunctions by means of a warning lamp (engine diagnosis indicator lamp (A1e58))
• Transmit errors via a uniform interface (diagnostic connector (X11/4)) to a diagnostic unit (e.g. Xentry Diagnostics)

The following goals are pursued by the OBD:

• Achieving permanently low exhaust emissions
• Protecting endangered components (such as CATs) against backfires

The following components and systems are monitored:

• Oxygen sensors
• NOx sensors on the left and right (N375b1/, N376b1/) (for engine 276.9 with code 920 (Gasoline direct injection with stratified charge))
• NOx sensor on the left and right upstream of NOx storage catalytic converter (N37/9b1, N37/10b1) (for engine 276.8 with code 920 (gasoline direct injection with stratified charge))
• NOx sensor downstream of NOx storage catalytic converter (N37/11b1) (for engine 276.8 with code 920 (Gasoline direct injection with stratified charge))
• Efficiency of catalytic converters (catalytic converter function)
• Catalytic converter heating
• Purging
• Smooth running analysis (recognition of combustion misfires)
• EGR (for code 920 (Gasoline direct injection with stratified charge))
• Other emissions-relevant components or such components a malfunction of which prevents diagnosis of other components

Function sequence for European OBD 

The OBD is described in the following points:

• 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 a limit value (e.g. 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 

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

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.

Here individual components 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 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-adjustment of mixture formation
• Smooth running analysis (recognition of combustion misfires)
• Catalytic converter function
• Oxygen sensors (aging and controlling)
• NOx sensors on the left and right (for engine 276.9 with code 920 (Gasoline direct injection with stratified charge))
• Right NOx sensor upstream of NOx storage catalytic converter (for engine 276.8 with code 920 Gasoline direct injection with stratified charge))
• NOx sensor downstream of NOx storage catalytic converter (for engine 276.8 with code 920 (Gasoline direct injection with stratified charge))
• Oxygen sensor heater
• Purging
• EGR (for code 920 (Gasoline direct injection with stratified charge))

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)
• NOx sensors on the left and right (for engine 276.9 with code 920 (Gasoline direct injection with stratified charge))
• Right NOx sensor upstream of NOx storage catalytic converter (for engine 276.8 with code 920 Gasoline direct injection with stratified charge))
• NOx sensor downstream of NOx storage catalytic converter (for engine 276.8 with code 920 (Gasoline direct injection with stratified charge))
• Oxygen sensor heater
• Purging
• EGR (for code 920 (Gasoline direct injection with stratified charge))

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
• Automatic transmission (fitted with its own OBD 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 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 component 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
• EGR (for code 920 (Gasoline direct injection with stratified charge))
• NOx sensors on the left and right (for engine 276.9 with code 920 (Gasoline direct injection with stratified charge))
• Right NOx sensor upstream of NOx storage catalytic converter (for engine 276.8 with code 920 Gasoline direct injection with stratified charge))
• NOx sensor downstream of NOx storage catalytic converter (for engine 276.8 with code 920 (Gasoline direct injection with stratified charge))

If the test readiness of individual systems or components 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, which have just been detected, are stored temporarily until confirmation (occurrence in two driving cycles once after the other) in the form of a DTC, the so-called DTC (Diagnostic Trouble Code), in the OBD.

If am 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 a maximum of 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
• Intake manifold pressure
• Intake 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 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 diagnostic connector is networked via chassis CAN 1 and diagnostic CAN (CAN D) with the ME-SFI [ME] control unit. 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.

	Electrical function schematic for OBD	MODEL 207	PE07.10-P-2720-97EAK
		MODEL 212	PE07.10-P-2720-97DAQ
		MODEL 218	PE07.10-P-2720-97XAI
	Overview of system components for gasoline injection and ignition system with direct injection	ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 as of model year 2014	GF07.70-P-9998MM
		ENGINE 276.8 in MODEL 207, 212 as of model year 2014 ENGINE 276.8 in MODEL 218 as of model year 2015	GF07.70-P-9998MMP