P2605: Intake Air Heater B Circuit/Open

What it means

The controller cannot drive the secondary intake air heater (heater grid B) used on diesel engines for cold-start support. The grid stays cold so cold-start emissions and white smoke increase.

At a glance

• Usually lights the check-engine light

How it works

Diesel engines may use a grid-style intake air heater to warm incoming air for cold starts; heater B is the secondary heater circuit. The controller checks whether that circuit can be driven, and sets P2605 when it detects an open path, such as a broken heater element or relay coil. With heater B unavailable, cold starts can produce longer cranking, rough running, or extra white smoke.

Common causes

Most likely first.

1. Open heater grid element
2. Failed heater relay or open coil

Symptoms

• Check-engine light
• Longer cranking or hard starting in cold weather
• Rough running or increased exhaust smoke after a cold start

How to diagnose it

1. Use a scan tool to record freeze-frame data and check whether the fault occurred during a cold start, when the heater would be expected to operate.
2. With the engine off, inspect heater grid B, its relay, connectors, and wiring for loose connections, damage, or corrosion.
3. Check the heater B element for continuity using the manufacturer's procedure; an open element supports a failed grid.
4. Check the relay coil and its wiring for an open circuit, following the manufacturer's test procedure.
5. If the element and relay coil pass, trace the circuit between them and the controller for a break or poor connection.

Common fixes

• Repair a loose or damaged heater B connector.
• Repair an open or damaged wire in the heater B circuit.
• Replace the failed heater B relay.
• Replace the intake air heater B grid if its element is open.

Can I keep driving?

If the engine runs normally, driving in mild weather is usually possible, but cold starts may be difficult and produce extra smoke. Avoid relying on the vehicle in freezing conditions until heater B works.