ON-BOARD DIAGNOSTICS

On-board diagnostics (OBD) is the terminology given to very early engine management systems in the US, which evolved into OBDII for cars sold in America from 1996. European on-board diagnostics (EOBD) applies to petrol cars sold here from 2001 and diesels from 2003. Gendan reports that some Obdii-compliant diagnostic tools will not work with pre-2001 European cars – certain Ford, Jaguar and Volvo models are fine, but the company admits that it has had very limited success with older Vauxhalls, Peugeot/citroëns, Fiats and Rovers.

Confusingly, EOBDII means ‘enhanced on-board diagnostics – second-generation’, meaning that additional manufacturer-specific information can be gleaned from an OBD port if an EOBDII diagnostic tool is used.

Required by European Type Approval, a standardised EOBD port (shown at right) consists of a connector with 16 different pins, with manufacturers using different pins for different functions. Up until 2004, five different communication protocols were used: J1850 VPW, ISO 91412, J1850 PWM, KWP2000 (ISO 14230) and CAN (Control Area Network). All models type-approved after 2004 were required legally to use CAN for their engine diagnostics.

Along with the connector and protocol, fault codes (or DTCS) are standardised, with letters P (powertrain), B (body), C (chassis) and U (network) denoting the suspected location. As the universal codes are limited in number, manufacturers have developed their own codes that may or may not follow the generic classification. Additionally, your ability to read codes, other than those of the basic ‘P’, depends greatly on your vehicle and the standard of diagnostic equipment you use. You can look-up codes online, but ensure that you use credible sites. Gendan provides a comprehensive library of generic codes and those for the Volkswagen Group specifically at www.gendan.co.uk/codebank

Various car manufacturers have been lobbying for the removal of the EOBD port, which would lock-out aftermarket technicians and Diyers. Wendy Williamson from the Independent Automotive Aftermarket Federation (IAAF) told CM that this would be anti-competitive. She says that the European Parliament approved legislation earlier this year that would see the EOBD port remain accessible to everybody, not just manufacturers and their dealers, for the foreseeable future.