Just like any other North American car made after 1996, the Diablo has an On Board Diagnostic or "OBDII socket" for a OBDII scan tool.  Government mandated rules specify that after the check engine warning light comes on due to a fault, the engine control unit must record a specific error code. The purpose of this code is to give precise information to the service technician concerning the fault to allow its repair.

	Pin 2 - J1850 Bus+ Pin 4 - Chassis Ground Pin 5 - Signal Ground Pin 6 - CAN High (J-2284) Pin 7 - ISO 9141-2 K Line Pin 10 - J1850 Bus Pin 11 Airbag Controller Pin 12 ABS Controller Pin 14 - CAN Low (J-2284) Pin 15 - ISO 9141-2 L Line Pin 16 - Battery Power
Fig 1 OBDII Socket Pins

While the parameters, or readings, required by OBDII regulations are uniform, the auto manufacturers had some latitude in the communications protocol they used to transmit those readings to scanners. Naturally, each felt they had the one true way, so we have three different OBDII communications protocols in use.

As a rule of thumb, GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation).

Chrysler products and all European and most Asian imports use ISO 9141 circuitry.  Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns.

Note. I have indicated in Cyan color the pins used in a 6.0L Diablo. This is probably also the case for for more recent cars. I do not know what pins are used in earlier cars.

In order to determine what (if any) code the OBDII system is putting out one needs to have access to an

Fig. 2  INNOVA (model 3100) OBDII diagnostic scanner.

OBDII diagnostic scanner. These come in many forms. Ranging from large factory systems such as the one supplied by Snap-On Tools to small hand held ones such as the one supplied by INNOVA (model 3100) shown here (Fig 2).  

The best low priced model I found however is one made by Auto-X-Ray (www.autoxray.com). It not only allows easy data reading, resets settings every time , it has a PC cable hookup to review stored data on your Windows based PC. The larger factory machines can interoperate all 3 formats.  This is often not the case for the small handhelds. OBDII scan code supplied by the Lamborghini system is in the ISO 9141 format. This probably reflects its Chrysler origins -- the owners of Lamborghini at the time!  Note, the user can consult the LamboWeb's section Check Engine Light Warning Codes In A Diablo  to quickly get information on a few of the more common OBDII diagnostic messages without a scanner although the information is limited.

The OBDII socket in later Diablos is located on the drivers side foot well on the right side of the steering wheel column.  The socket is the same on all cars and will fit all OBDII readers (see fig. 4).