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U0299 Lost Communication With DC/DC Converter Control Module B

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

A second DC/DC converter, B, appears where a single support stage cannot serve every consumer or where two networks are fed separately. FCA documents the code: in PCM reflash bulletins 18-023-19 Rev. B and 18-020-21, covering 2019 Cherokee models with the 3.2 V6 and stop-start, U0299 is named as loss of contact to DC-DC converter 2. Next to it stand performance and over-temperature codes for converter 2 (P0EA5, P0EA6) and invalid data from converters A and B. Customers report a lit MIL and an engine that does not always restart after an auto stop; the remedy is new PCM software, not a new converter. With B missing, start-stop is typically withdrawn and voltage-sensitive electronics may reset during restarts.

Likely causes

Powertrain control module software (FCA update)
Supply, fuse or ground of converter B faulty
Bus wiring or connector to converter B damaged
Converter B internally failed, e.g. after overheating

Symptoms

  • Check engine lamp on
  • Engine does not always restart after auto stop
  • Start-stop function disabled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–2,000
Time0.3–4 h

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

Parts involved

dc dc converter module bvehicle bus wiring

Related codes

U0298U059AU0599P0EA5P0EA6

References: static.nhtsa.gov, static.nhtsa.gov.