U0259
NetworkModule Communicationlow severityLost Communication With Fuel Fired Heater Control Module
What U0259 Means
The vehicle's network has lost contact with the fuel fired heater control module. This is usually a wiring or module fault affecting the auxiliary heater.
Symptoms
- No or weak cabin heat
- Warning light on dash
- Auxiliary heater inoperative
Common Causes
- Faulty wiring or connector to heater module
- Failed fuel fired heater control module
- Blown fuse or power supply issue
- Corrupted CAN bus network
Diagnostic Steps
- Scan for related communication codes
- Check power and ground at heater module
- Inspect wiring and connectors for damage
- Test CAN bus continuity to module
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Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
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Serious DIY~$100
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Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
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