A glow-plug warning does not automatically identify a failed engine ECU. P0670 concerns the glow-plug controller’s control circuit; P0671, P0672, P0673 and P0674 identify the glow-plug circuits for cylinders one to four. Confirm the engine’s cylinder numbering and the scanner’s complete description before ordering parts.
One cylinder or several?
An isolated cylinder code calls for a different investigation from several codes logged together. Save all fault entries and note whether cold starting is slow, uneven or accompanied by smoke. Include the outside temperature and whether the fault disappears once the engine is warm.
For the VAG P0671 example, Ross-Tech identifies both the glow plug and its wiring as possible causes. The warning can accompany poor cold starting. P0671 technical reference.
Information that improves the assessment
- Engine code, mileage and the exact glow-plug part numbers fitted.
- Whether one plug, a full set or the control module has already been replaced.
- Battery and starting-system findings from the workshop.
- Circuit and connector results, including whether several cylinders share the same failure pattern.
Modern glow plugs are not all designed for direct battery voltage. Applying power as an improvised test can damage a plug or its controller. Use the manufacturer’s procedure, including the correct plug specification and control strategy.
When to contact AXION
If the warning returns after replacement, send the earlier invoice and scan rather than starting the diagnosis again from the dashboard lamp alone. Ask about an electrical assessment and browse the engine ECU guides. Electronic repair suitability depends on the actual module and confirmed fault.
Reviewed September 2026. Use the complete manufacturer-specific fault description and vehicle repair information.