DME 7.8 Diagnosis: Introduction: General

This manual is intended for trained automotive workshop personnel who have successfully completed Porsche training seminars on the respective systems and who possess the necessary theoretical and practical knowledge to perform work on complex systems. 

The basic prerequisite for all work on the DME is the acknowledgement and observance of safety regulations and warnings; these are contained in the chapter Notes on the following pages. 

This OBDII manual DME 7.8 covers the following vehicles:

• 911 (996) turbo models, as of model year 2001
• 911 (996FL) naturally-aspirated models, as of model year 2002
• Boxster (986FL) naturally-aspirated models, as of model year 2003

This manual describes diagnosis and troubleshooting for the engine control module installed in Porsche sports cars (OBD = On-Board Diagnosis). It describes the OBD II versions for naturally-aspirated and turbo engines (USA version) covering the full scope of diagnosis. This includes the EOBD (European OBD) and RoW (Rest of the World) versions that were adapted to the respective national laws or regulations regarding diagnosis.

The main differences between the OBD II and EOBD versions include the fuel tank leakage test required by law in the USA and the criteria for storing faults and activating the CHECK ENGINE light (abbreviated CE below), which is also referred to as the MIL (Malfunction Indicator Light).

The following functions are assured by the OBD II system:

• Detection of combustion misfiring
• Monitoring the efficiency of the catalytic converter
• Monitoring the fuel tank ventilation system
• Monitoring the fuel tank system for leaks
• Monitoring secondary air injection
• Monitoring the adaptation limits (e.g. of oxygen sensing, boost pressure control)
• Monitoring the oxygen sensors
• Monitoring the thermostat and water temperature sensor
• Monitoring positive crankcase ventilation (via oxygen-sensing adaptation)
• Monitoring the Tiptronic transmission control module
• Monitoring emission-relevant sensors and actuators associated with the DME (previous scope of OBD 1)
• Triggering the Check Engine light and storing faults in the memory
• Indication of monitoring readiness (readiness codes)
• Output of existing diagnostic trouble codes (DTCs)
• Storage of defined operating parameters in the event of a fault (including freeze frame)
• Functional checks of the OBD system (warm-up cycle, driving cycle)
• Communication with standardized control-module tester (scan tool) in the prescribed modes
• Standardized read-out of operating data, such as rpm, temperature, etc.

Digital engine control module DME 7.8 

DME 7.8 is a proven, highly reliable engine control module, which was specially adapted to suit Porsche requirements.

When the terminal 30 voltage supply is interrupted, the following control module values are deleted:

• All fault memory entries
• Freeze frames (ambient conditions; see following chapter) stored with the faults
• All adaptation values
• Learned values of the throttle adjusting unit
• Ready statuses of the individual diagnosis routines (see following chapter)

Bear in mind that programming the DME (e.g. loading a new data record) will also delete the values mentioned above.

Note on adaptation 

The DME control module must perform a learning and adaptation routine for the throttle valve adjuster if:

• the power supply to the DME control module was interrupted,
• the DME control module connectors were unplugged,
• a new DME control module was installed,
• the throttle valve adjuster was replaced,
• the DME was programmed.

To initiate adaptation:

1. Switch on the ignition for 1 minute without starting the engine. Do not press the accelerator (make sure that no carpet is pressing on the accelerator, for example).
2. Switch off the ignition for at least 10 seconds.

The following conditions must also be met, otherwise learning is not possible:

• Vehicle is stationary
• Battery positive voltage between 10 V and 16 V
• Engine temperature between 5°C and 100°C
• Intake air temperature between 10 and 100°C

Standardized DTCs according to ISO 15031 

Diagnostic trouble codes that can be issued by the control module are standardized according to ISO 15031. This ISO standard is based on SAE J 2012.

The fault code or DTC is always a 5-character alphanumeric value, e.g. P0100.

The first character (letter) of the code identifies the system which has set the code. A total of four system types are covered:

• P for powertrain (this is the first character for all OBD2 fault codes)
• C for chassis
• B for body
• U for future systems

The P codes are classified in 2 main categories according to ISO 15031:

• Uniformly standardised codes: P0XXX and P2XXX; these codes are identical for all manufacturers
• Manufacturer codes: P1XXX and P3XXX; only the first 3 characters are standardised here (example: P13XX for ignition-system diagnosis or misfire detection); the last two characters are freely selectable by the manufacturer.

Only the P codes are required for OBD II.

The standardised codes are subdivided as follows:

P0001 to P0299 Fuel and air metering

P03xx Ignition system and misfire detection

P04xx Additional emission control systems

P05xx Speed and idle air control

P06xx Computer and output signals

P0700 to P0999 Transmission

P2000 to P2299 Fuel and air metering

P23XX Ignition system and misfire detection

P24XX Additional emission control systems

P25XX Additional input signals

P26XX Computer and output signals

P27XX Transmission

P28XX Reserved

P29XX Fuel and air metering