P2029
Fuel Fired Heater Disabled
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.
- Check engine light: Not always
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Heater glow plug failedCommon
- Low battery voltage triggered lockoutPossible
- Fuel supply starved — empty tank or pump weakPossible
Parts involved
- Fuel Fired Heater
- Heater Glow Plug
- Heater Fuel Pump
P2029 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.