ON-BOARD DI­AG­NOS­TICS

Car Mechanics (UK) - - Diagnostics Masterclass -

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.

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