P2029: Fuel Fired Heater Disabled

What it means

The fuel-fired auxiliary heater (used to warm coolant or DEF on cold start) has been disabled by the control module — typically because of repeated start failures, low-voltage supply, or a self-protection condition.

How it works

A fuel-fired auxiliary heater burns fuel to provide heat, such as warming coolant or an emissions-fluid system in cold conditions. P2029 indicates that the heater has been disabled by its control system, commonly after failed starts, low supply voltage, or a protective shutdown.

Common causes

Most likely first.

1. Heater glow plug failed
2. Low battery voltage triggered lockout
3. Fuel supply starved — empty tank or pump weak

Symptoms

• Check-engine light
• Auxiliary heater may not operate
• Slower cabin or engine warm-up in cold weather

How to diagnose it

1. Check freeze-frame and heater status data for a lockout reason, prior start failures, or low-voltage events.
2. Verify the battery condition and charging system, since low voltage can disable heater operation.
3. Inspect the heater fuse, power and ground connections, wiring, and fuel supply for visible damage or restriction.
4. Check heater fault history and glow-plug operation using the manufacturer's diagnostic procedure.
5. After correcting the underlying issue, follow the manufacturer's procedure to clear a heater lockout and confirm it starts.

Common fixes

• Charge or replace a weak battery and correct any charging-system fault.
• Restore the heater's fuel supply if it is starved or restricted.
• Repair a damaged heater power, ground, or connector circuit.
• Replace a failed glow plug if testing confirms the fault.

Can I keep driving?

You can generally drive the vehicle, but the auxiliary heater may not operate, so cabin or engine warm-up can take longer in cold weather. Do not rely on it for heat or defrosting until operation is restored.