دائرة مفتوحة في أسلاك شمعات التسخين

A break in the wiring to one or more glow plugs, so the plug receives no current. The module usually monitors each plug's circuit individually, so the code often names which one — and that is worth reading before anything is removed, since it turns a bank of plugs into a single connection.

These circuits carry high current, so the failures are at the joints. The individual plug leads use a push-on or screw terminal at the plug itself, and heat cycling loosens and corrodes them; the strap or harness linking a bank is another common break. The plug's terminal can also pull off entirely when the lead is disturbed during other work.

The symptom is a hard cold start with white smoke that clears once running, and no fault at all in warm weather — these circuits only energise below a temperature threshold. Measure each plug's resistance at its own terminal, which separates a broken lead from a failed plug, and check the terminal is genuinely tight rather than merely in place, since a loose one heats and eventually burns off.