964 & 993 OBD1 - Pre-MY1996 Cars, Code list and how to read codes.

NOTE: This page is a DRAFT work in progress, may have errors, and the code list is incomplete. It is based on information related to the 964 and assumes the OBD system features were carried over to the early non-USA delivered 993.

The OBD1 systems were first mandated in 1991 and were driven by California regulation. It was the first system where diagnostic system features were mandated. The manufacturers were not required to use a standard interface with code readers. The breadth of information available from OBD1 cars was limited in comparison to the later OBDII compliant vehicles but still very useful in diagnosing emission and other systems issues.

The OBDI emissions-related codes can be read with or without a reader.

Here is how to read codes without a reader*:

(*The below I understand works for a 964 and it follows that it should also work for the pre-1996 OBD-1 993 although I have not tested it for either series of cars. In any event, Durametric software supports all vehicles in both series through the OBD port.)

1. With the engine off turn the ignition switch to the "ON" position.

2. Press the accelerator pedal all the way to the floor for 3-5 seconds.
3. Wait for the "Check Engine" light to flash, then release the accelerator pedal.
The car's computer will begin to flash the "Check Engine" light.
Count the number of flashes between and notice the pause between flashes.

In this case, code 24 is the "Oxygen Sensor"

How to clear codes:

1. With the engine off turn the ignition switch to the "ON" position.
2. Press the accelerator pedal all the way to the floor for 11 seconds.

Porsche 964 & Pre-1996 993 OBDC-I Emission-Related Fault Codes

Here are the modules accessible using Durametric Software & Cable:
1989 - 1994 Porsche 911 (964)

Module	ECU Identification	Information	Read Codes	Clear Codes	Actual Values	Activations	Commands	Coding*
Motronic 2.1 M00 - M04 (Engine)	Yes	No	Yes	Yes	Yes	Yes	No	No
Tiptronic	Yes	No	Yes	Yes	No	No	No	No
ABS / PDAS	Yes	No	Yes	Yes	No	Yes	No	No
Air Conditioning	Yes	No	Yes	Yes	No	No	No	No
Airbag - B01	Yes	No	Yes	Yes	No	No	No	No
Alarm	Yes	No	Yes	Yes	No	No	No	No

Special features for this car:

• Activation for brake bleeding procedure
• Activation for transverse lock