Diagnostic Guidelines (Start Here)

DEFECT LOCATION PROCEDURE
Initialization of Diagnostic Procedure
Communication with the Digital Motor Electronic (DME) and other vehicle control units is established with the use of a Diagnostic Scan Tool. Connect as per manufactures instructions.

If data transfer is interrupted, information appears on the display screen indicating the possible cause:

- Ignition not switched on
- Voltage supply for control unit < 10 V
- DME relay not supplied with B+ (if not, bypass terminal 30 and 87)
- Control unit not connected
- Diagnostic link defective
- Data traffic inhibited by a defective control unit in the vehicle

Diagnostic System Quick Test
The system quick test or "interrogation" checks all systems which have Diagnostic Trouble Code (DTC) capabilities and should be used to verify that other interelated systems are operating correctly. Defects in Electronic Transmission Control (EGS), Antitheft system (DWA) or the On Board Computer can also effect the Digital Motor Electronic (DME).

Diagnostic Trouble Code (DTC) Memory Inquiry
Systems which have been identified as containing DTC's during the system quick test require further interrogation. If several defect codes are stored, interrelationships can often be deduced, indicating whether the defect can be attributed to central causes. For example, a defective ground supply can lead to storage of the defect codes "temperature sensor, air mass meter, idle actuator, throttle potentiometer".

Diagnostic Trouble Codes (DTC) Tests
DTC test instructions explain and supplement the self-diagnostic system or scan tool error messages.
The number of the defect code indicates the pin assignments at the control unit. The defect can be in the vicinity of the component, the corresponding wiring or in the control unit. If defects occur for which no DTC is stored, these tests provide the opportunity of performing troubleshooting with the aid of the subsequent tests. Electronic Diagrams should always be used since they clearly show the interaction of various components. Diagnostic Trouble Code (DTC) Tests

NOTE: Troubleshooting without a thorough understanding of DME system operation may lead to misdiagnosis and needless expense. Always review the Description and Operation provided at the system and component levels and systematically follow the test instructions. Specialized training and diagnostic test equipment are recommended. Description and Operation

Component Quick Tests
Provides additional testing information and diagnostic aids.

Status Monitoring and Component Activation
Status Monitoring (Data Stream)
Inputs and outputs can be monitored independently of the defect code storage function. In this case, current values or operating statuses are displayed. If Status Monitoring takes place while the engine is running, DTC's may occur when an engine speed over 2000 rpm is exceeded.

Component Activation
To facilitate fast fault finding, various components can be activated by the diagnostic equipment in conjunction with the DME control unit. The response of components in perfect working order, including their supply lines, can therefore be indicated by electrical or acoustic means.

Irrespective of whether DTC's are stored or not, status monitoring and component activation should always be used for fault tracing.

Specifications
Specifications may be found for individual components. Compare actual values against values obtained during testing procedures.

CAUTION: Disconnect control units from the wire harness only with the ignition switched "Off". After renewed operation, neutral basic values are set in the control unit for idle and emission control. Any irregularities in engine operation can be corrected by means of renewed adaptations (new learned values) during a test run, in which an engine temperature of >176°F (>80°C) is reached.

The 88 or 55-pin universal adapter or equivalent should be used for picking-off signals from the DME control unit and from the engine wire harness. Perform wire checks only with the control unit or component connectors disconnected. Furthermore, the universal adapter should only be connected between the control unit and wire harness when no diagnostic procedure ([1][2]diagnostic connector not connected) is to be carried out since this can lead to malfunctions.