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P0670

Glow Plug Module Control Circuit

The control circuit between the engine controller and the glow plug control module reports a fault. The ECU can no longer reliably command the module that drives the glow plugs, so cold-start pre-heating may not run. On a diesel this causes hard starting, white smoke, and rough running until warm. Causes: open or shorted wiring between ECU and glow plug module, a failed module, or a power/ground fault at the module.

  • Check engine light: Yes
  • Emissions related: Yes
  • Repair difficulty: medium

Symptoms

  • Glow plug warning light on (often orange coil symbol)
  • Hard cold start or no start in cold weather
  • White smoke from exhaust during warm-up

Common causes

Ordered by how often each turns out to be the cause.

  • Glow plug control module faultyCommon
  • Wiring or connector faultPossible

Parts involved

  • Glow Plug Module
  • Module Wiring

P0670 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.