For details about identifying D4 issues, please read the D4 FAQ.

For further information, please see the discussion thread, here.

A lot is talked about the D4 connector as mysteriously it didn't appear on early Maintenance CDs and is nicely hidden away from view. However, it is very sensitive to atmospheric moisture, especially when driving through deep puddles. It is the connector for most communications from the engine bay to the dashboard.

To gain access, remove the battery cover, disconnect the battery, and then remove the fusebox retaining screw (1a) as shown below.
engine fusebox 1.JPG

The whole fusebox can be titled upwards or removed to reveal the wiring underneath, as below:

D4 is now accessible, and is shown below:

If it's waterlogged then disconnect the connector halves by moving the release catch on the connector (purple on this car) and allow to dry or use gentle heat from a hair dryer etc.

If it's dry and it's a poor contact you're suspecting then use contact cleaner (not WD40 - use electrical contact cleaner available at many large car accessory shops).

Allow it to dry thoroughly then reconnect by just placing the two halves together and then let the release catch do the work of pushing the halves back together.

Once you're sure you've finished your job and fixed everything then I would advise you to wrap the whole connector and the incoming cables in cling film or similar just like a party cracker and tie the ends up with cable ties - BUT, I would advise just put a couple of very small pin pricks in the top of the cling film so that it can breath as damp and condensation are the enemies of this connector.