Cause
Heat damage to wiring insulation
Insulation hardened, cracked or melted by proximity to something hot — an exhaust manifold, a turbocharger, a heater element, or an EGR component. The damage is cumulative over years of heat cycling rather than a single event, which is why it appears on older vehicles and in the same handful of places on any given model.
It produces intermittent faults before permanent ones, and that sequence is the diagnostic clue. Cracked insulation conducts to earth only when it is damp, or only when the loom moves and the crack opens. A fault that comes and goes with the weather, or over bumps, on a wire that runs near something hot, is this.
Heat also causes it from the inside. A circuit carrying current through a marginal connection heats that joint, which degrades the insulation around it, which raises resistance further. Connector housings that look scorched or discoloured have been declaring this for months — so inspect for browning rather than only testing continuity.
Repair means replacing the damaged section and re-routing or re-sleeving it, not taping over it. Insulation that has hardened once will keep failing along its length, and heat shielding that has gone missing — a common casualty of earlier repairs — should be replaced with it.
Typically a moderate job.
Codes this can cause (12)
Codes where this is a likely explanation first, rather than merely a possible one.
- P00C0 Turbocharger/Supercharger Bypass Valve B Control Circuit Likely for this code Moderate
- P040D Exhaust Gas Recirculation Temperature Sensor A Circuit High Likely for this code Moderate
- P04D0 Exhaust Gas Recirculation Temperature Sensor C Circuit Low Likely for this code Moderate
- P04D1 Exhaust Gas Recirculation Temperature Sensor C Circuit High Likely for this code Moderate
- P02E3 Diesel Intake Air Flow A Control Circuit High Moderate
- P02EE Cylinder 1 Injector Circuit Range/Performance High
- P02F0 Cylinder 3 Injector Circuit Range/Performance High
- P20C6 Reductant Heater D Control Circuit Performance Moderate
- P21C4 Reductant Heater Relay Control Circuit High Moderate
- P22CE Turbocharger Compressor Outlet Switching Valve Stuck Closed High
- P245D Exhaust Gas Recirculation Cooler Bypass Control Circuit High Bank 1 Moderate
- P24B5 Particulate Matter Sensor Heater Control Circuit Low Moderate
Information, not instruction
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