Cause
Disconnected connector
A connector left unplugged, or shaken loose, so the circuit is simply open. It deserves naming precisely because it is too obvious to check — a diagnosis reaches for a meter and a wiring diagram while the answer is visible from a metre away.
Recent work is the strongest predictor. A connector disturbed to reach something else and not refastened, a lock not clicked home, or one knocked off while another part was removed. A code that appears immediately after unrelated work, on a circuit near where that work happened, is this until proven otherwise — and the affected system is often nothing to do with the job that was done.
Vibration finishes what a poor refit starts. A connector pushed together without its lock engaged will hold for days and then part, so the fault appears long enough after the work for nobody to connect the two. Check that each connector's lock is actually latched rather than that it looks seated — the tactile click is the test, and a gentle pull confirms it.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0413 Secondary Air Injection System Switching Valve A Circuit Open Likely for this code Low
- P0416 Secondary Air Injection System Switching Valve B Circuit Open Likely for this code Low
- P0444 Evaporative Emission System Purge Control Valve A Circuit Open Likely for this code Low
- P0447 Evaporative Emission System Vent Control Circuit Open Likely for this code Low
Information, not instruction
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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.
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