Diagnosis fault memory, ME-SFI function

P07.61-2919-05

0100 DAS

K40/4 Passenger-side fuse and relay module (model 230)

K40/7 Right front fuse and relay module (model 215, 220)

N3/10 ME-SFI [ME] control unit

N10/1 SAM control unit with fuse and relay module for the driver (model 240)

N10/1 Front SAM control unit with fuse and relay module
(model 216, 221)

N73 EIS [EZS] control unit

X11/4 Data link connector

CAN Data bus

The ME-SFI [ME] control unit (N3/10) checks input and output signals for plausibility. Here it recognizes and differentiates between the following errors:

 Faults constantly present

 Loose contact fault (only on coolant temperature sensor (B11/4) and accelerator pedal sensor (B37))

The following components and systems are monitored:

 Left and right O2 sensors upstream and downstream of TWC
(G3/3, G3/4, G3/5, G3/6)

 Catalytic converter function

 Catalytic converter heating

 Secondary air injection

 Smooth running control (combustion misfire)

 Fuel system

 Control units which are linked via the CAN data bus system

Driving cycle

Systems that are not constantly monitored are checked only when a driving cycle is executed.

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A driving cycle for a test consists of:

 Engine start (cold start)

 City cycle

 Outer city cycle

 Engine switch-off

As the required operating conditions are not always given, all the tests are also not completed in one drive.

Fault recognition

The following faults and error states are detected:

 Signals above or below the limit value
(open circuits, short circuits, faulty sensor)

 Frequency of fault

 Illogical combination of signals

 Function chains with faults

 Fault messages all via the CAN data bus system transmitting control units

 Fault conditions of alternator (G2)

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Engine diagnosis indicator lamp (A1e58) or for  CHECK ENGINE indicator lamp (A1e26)

If there is an exhaust-related fault in two consecutive driving cycles, the indicator lamp in the instrument cluster lights up (A1). In the event of a fault which could damage the catalytic converter, the engine diagnosis indicator lamp flashes.

The indicator lamp goes out after 3 correct, successive driving cycles.

Fault storage

Faults detected are stored with its fault freeze frame data together in the fault memory. If the fault is not confirmed during the following driving cycle, it is deleted. Emission-relevant faults are always entered, they have a high priority.

After 40 correct driving cycles, a stored exhaust gas relevant fault and after 80 correct driving cycles, a TWC damaging fault is erased from the fault memory.

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Read out the fault memory

The ME-SFI [ME] control unit is connected via the CAN or a K-line to the datalink connector (X11/4). Stored faults can be read out and deleted using DAS or with a standard output device (generic scan tool) for "Ignition ON" or with the engine running via the datalink connector (SAE standard ISO 9141-2).

The fault memory is not erased if the battery or on-board electrical system battery (G1) is disconnected.

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Exhaust gas relevant fault from the automatic transmission are no longer sent to the ME-SFI [ME] control unit from 06/2007 but are administered and stored by the ETC [EGS] control unit (N15/3) itself.

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Fault freeze frame data (operating conditions)

If a fault is detected, the following data are stored:

 Fault code

 Vehicle speed

 Engine speed

 Coolant temperature

 Air mass

 Engine load status

 Throttle valve angle

 Ignition angle

 Gear selected

 Mixture formation adaptation value

 Lambda control status (enabled, not enabled, locked during fuel shutoff, locked during fault detection, without correction of left and right O2 sensor downstream of TWC (G3/6, G3/5))

 Environmental conditions (e.g. fuel tank level, distance in the case of fault entry, counter readings for fault frequency, purge system or air injection system active)

 Alternator voltage

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Function chains are test sequences triggered by the ME-SFI [ME] control unit, for example, for air injection, regeneration and

consequential faults

If a faulty signal is detected and the corresponding fault code is stored, all the tests in which the signal is required as a comparative parameter, are ended. This ensures that no consequential faults are stored.

Readiness code

This code makes it possible to recognize that tests relating to fault recognition are in progress and the system is thus active.

The code is set once the following tests are completed (result of test not significant):

 Catalytic converter effect

 Purge control

 Secondary air injection

 O2 sensor signal and heating upstream of TWC

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Emergency running

If a fault is detected, substitute values are formed for the emergency running and the engine diagnosis/CHECK ENGINE indicator lamp lights up.

ME-SFI [ME] control unit run-on

After faults are erased it is necessary to wait until the processor has completed its power-down sequence after the ignition is switched off.

The duration is adaptable (programmable) and is about 5 s.