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

Engine 177.9 in model 205, 253

Engine 177.9 in model 213

up to model year 2021

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 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 into 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
Display malfunctions using symbols in the IC (A1)
Transfer identified faults over a uniform interface (diagnostic connector (X11/4)) to a diagnostic equipment

EOBD pursues the follow objectives:

Achieving permanently low exhaust emissions
Protecting endangered components (such as CATs) 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
Avoiding consequential faults
Saving the fault freeze frame data
Fault message
Read out fault memory
Fault deletion

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
Loose contact (e.g. occurred during driving)

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

Measurement values which are above or below the limit value (e.g. short circuit, open circuit, defective sensor)
An illogical combination of various measurement values, 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 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
Left oxygen sensor element upstream of CAT (G3/3b1)
Left oxygen sensor heater upstream of CAT (G3/3r1)
Right oxygen sensor element upstream of CAT (G3/4b1)
Right oxygen sensor heater upstream of CAT (G3/4r1)
Left oxygen sensor element downstream of CAT (G3/5b1)
Left oxygen sensor heater downstream of CAT (G3/5r1)
Right oxygen sensor element downstream of CAT (G3/6b1)
Right oxygen sensor heater downstream of CAT (G3/6r1)

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 systems and components are monitored cyclically:

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

Continuous monitoring

Continuous monitoring means continuous 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 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 the previous driving cycle are temporarily stored in the EOBD in the form of a fault code, the so-called Diagnostic Trouble Code (DTC) 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 are, for example:

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

If a malfunction occurs in two successive driving cycles, the engine diagnosis indicator lamp (A1e58) (model 205, 253) or the engine diagnosis indicator lamp (model 213) lights up in the instrument cluster. 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/appears permanently during the whole (remaining) driving cycle. Fault message by means of the engine diagnosis indicator lamp disappears automatically after 3 consecutive trouble-free driving cycles. The ME-SFI [ME] control unit transmits the request for actuation of the engine diagnosis indicator lamp via the drive train CAN, the powertrain control unit, the chassis FlexRay, the electronic ignition lock control unit and the 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.

Avoiding consequential faults

If a faulty signal is recognized and stored, all tests are broken off for which this signal serves as a comparative value (so-called transverse locking). Saving of consequential faults is thereby prevented.

Saving the fault freeze frame data

Fault freeze frame data are, for example:

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

Fault message

The engine diagnosis indicator lamp in the instrument cluster is actuated by the ME-SFI [ME] control unit via drive train CAN (CAN C1), powertrain control unit (N127), chassis FlexRay (Flex E), electronic ignition lock control unit (N73) and user interface CAN (CAN HMI). 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.

Read out fault memory

The ME-SFI [ME] control unit is connected via drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and diagnostic CAN (CAN D) to 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 codes, can be read out using a diagnostic tester over the diagnostic connector.

Fault deletion

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

Electrical function schematic for electrical European On-board Diagnosis	Engine 177.9 in model 205, 253	PE07.10-P-2720-97FBD
Electrical function schematic for electrical European On-board Diagnosis	Engine 177.9 in model 213 up to model year 2021	PE07.10-P-2725-97DBG
Overview of system components for gasoline injection and ignition system with direct injection	Engine 177.9 in model 205, 253	GF07.70-P-9998MNA
	Engine 177.9 in model 213 up to model year 2021	GF07.70-P-9998MNE