Why does this happen? No one can say for sure. But it’s important to understand that these wires operate under extreme conditions. In cold weather, temperatures can range from –30 °C to +90 °C. Harsh environmental exposure and constant vibration contribute to aging. As the mileage approaches a million kilometers, the insulation starts to crack, wires can break, and sealing gaskets may begin to leak oil. In such cases, not only the wiring but also protective corrugations and other parts of the engine become drenched in oil. Hot, dripping oil’s impact on engine components is self‑evident.

So, how to prevent all this? You can’t—at least not entirely. But you can minimize the chances of these unpleasant surprises by using high-quality parts and keeping the engine from overheating.

If repair becomes necessary, you're likely to be offered one of three common options:

Official repair kit: Any authorized dealer will suggest buying a complete Volvo repair set for the wiring harness. The job is done quickly, with minimal risk of human error, and includes a Volvo warranty. The downside? New wiring and labor are expensive, and parts may need to be ordered—lead times can range from 1–3 days, or sometimes even a month.

DIY wiring harness: A solid, cost-effective solution where you replace all wires and connectors both at the ECU and injectors. It’s a reliable and cheaper alternative.

Replace only the wires under the valve cover: You only replace the injector-side connectors. It’s the most popular and cheapest method. Just be sure to use high-quality parts—some unscrupulous sellers offer what they claim are “garage‑repaired” wires and contacts. DIY insulation often fails quickly, unlike original or even remanufactured factory wiring.

The same applies to connectors. Injectors carry high current, so improper installation or low-quality components will lead to another wiring failure.

Wires must be thick, robust, and heat-resistant. When replacing wiring gaskets, new ones are strongly recommended—though they can be expensive. Silicone heat-resistant sealant or oil-resistant gaskets may work if applied correctly. With proper methodology, they perform well and maintain wiring integrity.