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U029F Lost Communication With Evaporative Emission System Leak Detection Control Module

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

Some evaporative systems run the leak test through a separate module that holds its own valve, pressure switch or sensor and reports results to the engine controller. U029F is stored when those reports no longer arrive. Kia documents it for the Niro hybrid of 2017 to 2019: bulletin PS593 describes a MIL with U029F00 and, on cars built before October 2018, asks for a resistance check of the yellow signal wire between pin 12 of joint connector EF11 and pin 2 of the natural vacuum leak detection plug F56, since damaged insulation or corroded strands near F56 cause an open circuit. Ford's 2014 code list marks the code as a MIL code. CARB 1968.2 requires gasoline vehicles to find leaks as small as 0.020 inch, so the EVAP monitor cannot run. Driving is not affected.

Likely causes

Damaged insulation or corroded strands in the module signal wire

Corrosion or water at the leak detection module connector

Supply or ground of the leak detection module interrupted

Leak detection module internally failed

Symptoms

MIL on
EVAP readiness not set
No noticeable change in driving

Repair estimate

DifficultyMediumDIY possible

Parts and labour€30–400

Time0.5–2 h

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

Parts involved

evap leak detection modulevehicle bus wiring

Related codes

U05A0 U030A P0455 P0456 P2401

References: static.nhtsa.gov, performanceparts.ford.com, law.cornell.edu.