Hand-Held Tester (HHT)

Fault search with Hand-Held Tester (HHT)
Diagnostic trouble code (DTC) memory: Select "Current DTC's". If the actual condition changes, e.g. when wiggling a connector, the change is reported optically and acoustically so that troubleshooting can be performed directly with the HHT.

Loose connections
Loose connections are stored if they occur several times in a certain time period. Therefore, they can appear only as "Stored DTC's" and never as "Current DTC's".

Nominal values
All nominal values relative to the actual values shown on the HHT are listed in General Test and Adjustment Data. Test and Adjustment Data [Specifications]

Actual values for coolant temperature, intake air temperature and air mass
In case of an open or short circuit, the actual value is immediately replaced by a substitute value which is very close to the actual value. Therefore, a fault can not be recognized clearly. A readout of the fault is possible only via the diagnostic trouble code (DTC) memory.

Actual value for engine rpm
In case of the engine rpm's, the HHT display shows the closed throttle (idle) speed nominal value calculated by the control module on the left and on the right, the rpm actual value. Both values should differ from each other only slightly. The permissible tolerances are not yet known.

Version coding with HHT starting 03/94 (up to HHT Diagnosis Identification 45)
a) Before replacement of the engine control module, the existing code number must be read and stored with the HHT (menu selection 6 "Version coding"). After installation of the new control module, the previously read code number must be entered.

NOTE: If returning a new control module to a parts distribution center (PDC), the code number must be erased.

b) If the code number can not be read, the vehicle equipment/version must be determined, the corresponding code number obtained from the Spare Parts Microfiche, Group 54 and manually entered with the HHT.

c) When performing a trial installation of a control module with the same part number from another vehicle (up to model year 1995), but with a different code number, the following must be observed:

- Read and record code number from vehicle with complaint.
- Exchange control modules.
- Read and record code number from the exchanged control module.
- Enter the code number from the original control module into the exchange control module.
- Perform function test.
- Before returning control module to other vehicle, enter recorded code number into exchange control module.
- Exchange control modules.

Drive authorization system, stage 2 (DAS)
Upon replacement the engine control module must be version coded using the HHT. Additionally, the code number and VIN must be entered (see HHT nominal values "DAS", menu selection 3/6).