P2604 Intake air heater: reading or operation not right ("A")

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

P2604 means: Intake air heater: reading or operation not right ("A"). Glow plugs heat the diesel engine's cylinders for cold starts. Drive gently and have the car checked soon. The repair usually costs about €40–400 in Estonia. The most common cause: burnt-out glow plug. Other possible causes: glow plug module or relay, wire or connector at the plug.

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. There is a signal, but the reading or operation isn't plausible. The cause may be the part itself or a real mechanical fault.

What you may notice

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

What could be wrong

1. 1Burnt-out glow plug
2. 2Glow plug module or relay
3. 3Wire or connector at the plug
4. 4Fuse

Repair difficulty: Moderate

What you can check yourself

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 measure each plug's resistance
2. We check the module and wiring
3. We replace the plug or module

Standard SAE description: Intake Air Heater "A" Circuit Range/Performance