Random Fault Codes Regarding Misfires on VW 1.9 PD Applications

Vehicle Applications

Summary

Intermittent codes, for example 18074 /5 /6 /7 (cylinder x misfire) can randomly occur and in some cases be single or multiple incidences.

This fault code type is more likely to arise with older or high mileage vehicles as the injector wiring loom is internally mounted on the cylinder head and subjected to temperature extremes, vibration and lube oil, causing degradation of the connectors.

Resolution

Vehicles displaying this type of fault can be readily diagnosed by doing a “wiggle” test on both the main harness connector and the injector connectors while checking for continuity. The injector loom is available as a service part, and can be fitted in place, but the security of the main loom connector must be checked. This is best done by using an old connector of the same type and probing the connector to check for security.

It is possible to tighten the connectors, but in either case a further wiggle test is advised after repair to ensure continuity exists from the main connector to the injectors. Where possible a continuity test can be done at the ECU harness to validate the complete circuit.

Most likely failures will be the connectors and also the most cost effective to repair. In all cases the security of the wiring must be confirmed as further mechanical intervention is costly.

However if the Unit injector is suspected, the coil resistance can be checked on each individual injector. Typically this should be 0.3 to 0.7 ohms on the injector connections with the loom disconnected. Short to ground should also be checked between each terminal and the injector body.

If any injector is open or short circuit then the item must be replaced. A fully serviced / exchange / new item should be available at your local Diesel Centre, who can also provide “on bench” diagnostic and repair for unit injectors.

Tools & Equipment