Troubleshooting with HHT
DTC memory: Selecting current faults
If the current condition changes, e.g. due to the loosening of a connector, the change is signalled visually and audibly so that troubleshooting can be carried out directly with the HHT.
Loose contacts
Loose contacts are stored if they occur several times over a specific period of time. They can therefore only appear as stored faults and never as current faults.
Specified values
All specified values relating to the actual values displayed in the HHT are given in the chapters "Fuel injection and ignition system (PEC) diagnosis, function check using actual values".
Actual values of engine coolant/intake air temperature
In the event of an open-circuit or short-circuit, the system switches over immediately from the current actual value to a substitute value which is very close to the actual value. Consequently, a fault cannot be clearly recognized. It is only possible to read out the fault via the DTC memory.
Actual value of intake manifold absolute pressure
If there is no intake manifold absolute pressure at the control module or a defect in the pressure sensor in the control module the system switches over immediately from the current actual value to a substitute value which is very close to the actual value. Consequently, a fault cannot be clearly recognized. It is only possible to read out the fault via the DTC memory.
Actual value of engine speed
For the engine speed, the specified idle speed value calculated by the control module appears on the left of the HHT display and the actual engine speed value appears on the right. The values should only deviate slightly from each other. The permissible tolerances are not yet specified.