Glow plugs (diesel)

What it means

Glow plugs are small heaters in each cylinder of a diesel engine. They warm the combustion chamber so the engine starts easily when cold. These codes mean a glow plug, its control unit or the wiring has failed.

Codes in this group

Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.

What you may notice

• Hard starting on cold mornings
• White smoke and rough running for the first minute
• Glow plug lamp flashing or staying on
• Little or no symptom in warm weather

Common causes

Most likely first:

• A burnt-out glow plug (they wear out)
• A failed glow plug relay or control module
• Corroded wiring or connector

What to check first

• In a warm climate the car will usually start normally, so this can wait a short while
• Glow plugs can seize in the cylinder head: removal is best left to a workshop

Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.

After the repair

Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.

Related codes

Crankshaft and camshaft timing do not agree (P0016), Engine misfire (P0300), Knock sensor (P0325), Crankshaft position sensor (P0335), Camshaft position sensor (P0340), Ignition coil circuits (P0350). All codes.

Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.