Notes on HHT
Loose contacts
Loose contacts are stored if they occur several times over a specific period of time. They can therefore only occur 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 Engine Diagnosis Manual, Chapter A.
Actual values of engine coolant 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 the fault from the fault memory.
Actual value of engine speed
For the engine speed, the specified idle speed value calculated by the control module appears under menu item 3/1 Closed throttle position on the left of the HHT display, and the actual engine speed value appears on the right.
Actual value of injected fuel quantity
For the injected fuel quantity, the specified injected fuel quantity value calculated by the control module appears under menu item 3/2 Testing engine, on the left of the HHT display and the actual injected fuel quantity value appears on the right.
Actual value of rail pressure
The rail pressure appears under menu item 3/2 Testing engine on the HHT display. The specified value of rail pressure calculated by the control module appears on the left and the actual value of rail pressure appears on the right.
The values should only deviate slightly from each other. The permissible tolerances are not yet specified.