U01B6 Lost Communication With Fuel Heater Control Module

A fuel heater warms diesel ahead of the filter so that paraffin wax, which separates out in the cold, cannot clog the element; ordinary diesel turns to gel at roughly −15 to −19 °C. Newer designs use a microcontroller: a patent describes a heater controller that sets power from outside air temperature in open loop or from fuel temperature in closed loop, and cuts out when battery voltage falls too low. Where such a unit reports to the engine controller over the network, U01B6 means it has stopped answering and the heater state is unknown. No manufacturer documents this code publicly, and whether a MIL follows depends on how the maker rates the heater for emissions. In frost, expect hard starting, power loss or stalling from a waxed filter; in mild weather often nothing is noticed.

Likely causes

Symptoms

• Hard starting or stalling in frost
• Power loss from a clogged fuel filter in cold weather
• Often no symptom in mild weather

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: patents.google.com, en.wikipedia.org.