OBD II Task/Design/Function

Design

10 Inline injection pump
B11/4 Coolant temperature sensor
B17 Intake air temperature sensor
B28 Pressure sensor
B28/3 EGR lift sensor
L5/6 Crankshaft position sensor
N3/7 IFI control module
R25/2 Accelerator pedal position sensor
Y1/1 IFI electrohydraulic shutoff
Y1/1b1 Fuel temperature sensor
Y22/6 Resonance in take manifold switchover valve
Y22/7 Resonance intake line switchover valve
Y23/1 IFI fuel metering control
Y23/1I1 Fuel rack position sensor
Y31/1 EGR vacuum transducer
Y31/2 Pressure regulating flap vacuum transducer


NOTE: The on board diagnosis II (OBD II) functions are stored in the IFI control module (N3/7).


Task
Recognizing and storing faults in the fuel injection system. In addition, the ambient conditions which exist at the moment the fault occurs, are stored.

Function

Fault path tests
In certain operating states, fault paths are checked e.g. for short circuit, open circuit, implausible signals and illogical combination.

Notes refault memory
- Fault memory: fault readout
current faults: are displayed against a grey grid
stored faults: are highlighted

All inputs/outputs are checked for plausibility during operation. Any fault which occurs, is stored in the fault memory of the IFI control module (N3/7).
The faults remain stored at ignition "OFF" or after disconnecting the car battery.
In the case of exhaust-relevant faults the malfunction indicator lamp
CHECK-ENGINE (A1e26)
comes on and the following readout appears in the multifunction display:
CHECK-ENGINE
ENGINE ELECTRONICS.
The faults are identified with an OBD fault code.
Such faults are e.g.:
- Lift sensor B28/3
- EGR vacuum transducer Y31/1
- Pressure regulating flap vacuum transducer Y31/2

Fault ambient data
When using the HHT, it is also possible to additionally display the fault ambient data at the moment the fault was stored. Only the ambient data which where present when the fault first occurred, are stored. The ambient data are spread over several image pages (up to 8 image pages), the last two image pages being intended solely for the Development. Image pages with the result V/F explain the causes of the fault e.g.:
- voltage too high
- voltage too low
- signal too large
- signal too small
- value implausible

Definition: test readiness
Appropriate fault path tests and function chains must have been conducted completely at least once after ignition ON to ignition OFF (one operating cycle). Consequently, two "completed" tests can only be achieved in two operating cycles.

Operating cycle
An operating cycle is achieved if the
- coolant temperature > 60° C
- engine speed 5 s at 2500 rpm
- ignition 5 s OFF
- engine 5 s at 2500 rpm
- ignition 5 s OFF
- engine speed 5 s at 2500 rpm
see HHT Menu 3/8 Test Readiness OBD II