Cause
Heat-damaged wiring insulation
Insulation hardened, cracked or melted by proximity to a heat source, so conductors are exposed or shorting. It is a slow failure with an abrupt end — the insulation embrittles over years and then cracks, so the fault appears suddenly on a harness that has been degrading since it was built.
Where it happens is predictable. Against an exhaust manifold, near a turbocharger, across a downpipe, or where a heat shield has corroded away or been left off. A harness that is stiff and shiny rather than flexible has been cooked, and it will crack wherever it is bent — including during the inspection.
The fault is usually a short to earth if the conductor reaches metal, or an intermittent short between adjacent wires inside the loom, which produces genuinely bizarre symptoms as one circuit drives another. Repair the whole affected length rather than the visible break, because insulation that has reached this state has done so along its whole exposed run — and refit or replace the missing heat shield, or the repair cooks too.
Typically a moderate job.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Others who found this
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about Heat-damaged wiring insulation.