On-Board Diagnosis (OBD) ME - function - GF07.61-P-1001SM

ENGINE 113.986 with CODE (494) USA version 

ENGINE 113.987 with CODE (494) USA version 

ENGINE 113.988 with CODE (494) USA version 

ENGINE 113.989 with CODE (494) USA version 

O  n-B  oard D  iagnosis (OBD  ) means:

• Monitoring components relevant to the exhaust gas quality and systems while driving
• Establishing malfunctions and storing them
• Indicate malfunctions by means of an indicator lamp (MIL)
• Transfer detected faults in the workshop over a uniform interface to a scantool
• Protecting endangered components (such as catalytic converters)

The following components and systems are monitored:

• Oxygen sensors
• Three-way catalytic converters
• Catalytic converter heater
• Secondary air injection
• Exhaust gas recirculation
• Smooth running control (combustion misfires)
• Fuel system
• Tank venting system
• Control units (which are networked over the CAN databus)

The ME-SFI control unit (N3/10) checks its input and output signals for plausibility and detects possible faults.

The detection of faults and their storage is differentiated as follows:

• Faults constantly present

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

Driving-cycle 

Systems which are not monitored permanently are first checked when passing through a driving cycle.

A driving cycle for a test consists of:

• Engine start (cold start)
• City cycle
• Extra-urban cycle
• Engine switched off

The fact that not all required operating conditions are always present means that not all checks are conducted during a test drive.

Fault recognition 

The following faults and fault states are recognized:

• Signal above or below the limit value (broken lines, short circuit, defective sensor)
• Frequency of occurrence of the fault
• Illogical combination of signals
• Function chains with errors
• Error messages for all systems (control units) connected over the CAN databus
• Fault states for the generator (G2) with interface controller

"CHECK ENGINE" MIL 

If a fault occurs which is relevant to the exhaust gas quality or if it was already been stored during the last driving cycle then the "CHECK ENGINE" MIL (A1e26) lights up in the instrument cluster (A1). The indicator lamp flashes for a catalytic converter damaging fault.

The indicator lamp goes out after 3 consecutive fault-free driving cycles.

Fault storage 

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

A fault which is relevant to exhaust gas quality with be deleted from the fault memory after 40 fault-free driving cycles and a catalytic converter damaging fault with be deleted from the fault memory after 80 fault-free driving cycles.

Reading out fault memory 

The ME-SFI [ME] control unit is connected over the K-line (K) and the central gateway control unit (N93) to the data link connector (X11/4). The stored faults can be read out using the STAR DIAGNOSIS (0100) or standard read-out device

(Generic Scan Tool) for "Ignition ON" or for a running engine over the data link connector (SAE standard ISO 9141-2) and then deleted.

The fault memory is not  erased if the vehicle battery is disconnected.

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 state
• Throttle valve angle
• Ignition angle
• Gear selected
• Adaptation value of mixture formation
• Status of lambda control
  • Lambda control not enabled
  • Lambda control enabled
  • Lambda control inhibited if fuel shut off
  • Lambda control inhibited if fault detected
  • Lambda control without correction of O ₂ downstream of the TWC (G3/5, G3/6)
• Environmental condition (z. B. tank level; distance traveled for a fault entry; counter readings for frequency of occurrence of faults; exhaust gas recirculation, purging or air injection active)
• Generator voltage

Function chains  are test sequences, e.g. for air injection, purge system and leak-tightness of evaporative emission control system, activated by the ME-SFI control unit.

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
• Regeneration
• Air injection
• O₂ sensors upstream of TWC (G3/3, G3/4), signal
• O₂ sensor upstream of TWC, sensor heater
• Exhaust gas recirculation

Emergency running 

If a fault is detected, substitute values for limping-home are formed and the "CHECK ENGINE" MIL lights up.

ME-SFI control unit run-on 

After faults are erased, it is then necessary to wait until the processor has completed its run-on after the ignition is switched off.

The time is dependent on the coolant temperature and is about 150 seconds for -30°C and about 30 seconds for 80°C.

	ME-SFI [ME] control unit component description	N3/10	GF07.61-P-6000SM
	"CHECK ENGINE" MIL Component description for "CHECK ENGINE" MIL	A1e26	GF54.30-P-5011SM