P0383 Glow plugs: signal or voltage too low

By: Diagno editorial team · Updated: 2026-10-15

P0383 means: Glow plugs: signal or voltage too low. Glow plugs heat the diesel engine's cylinders for cold starts. Drive gently and have the car checked soon. The most common repair costs about €45–90 in Estonia, depending on make and model. The most common cause: connector loose, damp or corroded.

What it means

Glow plugs heat the diesel engine's cylinders for cold starts. The computer found a fault in a plug or the glow plug module circuit. The signal voltage is too low. Usually a wire is broken, a connector is loose or a wire is shorted to ground.

What you may notice

• Hard cold starts
• White smoke after starting
• Glow plug light flashing

What could be wrong

1. 1Connector loose, damp or corroded · Wiring or connector repair €45–90
2. 2Wire broken or shorted to ground · Wiring or connector repair €45–90
3. 3Faulty glow plug or its module · Control unit check and software €150–300
4. 4Engine computer fault (rare) · Control unit check and software €150–300

Repair difficulty: Moderate

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? In cold weather start the engine only once the glow plug light has gone out. Fix it before the frosts if you can. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the glow plug or its module

Standard SAE description: Glow Plug Control Module Control Circuit Low