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U0115 Lost Communication With ECM/PCM B

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U0115 is set when a second engine or powertrain controller, ECM/PCM B, vanishes from the bus; U0100 belongs to unit A. What B stands for depends on the maker: GM's Saab 9-5 and 9-4X lists call it ECM 2, Mercedes-Benz assigns U011500 to its drivetrain control unit. In the 2021 S 580, the 48 V integrated starter alternator logged U0115 with U0168 because of its own software; the MIL went out after three drive cycles, release 20.B cured it (LI15.40-P-073663). The DC/DC converter of the EQB and electric G-Class records it after wake-up faults (LI54.10-P-079533). Mazda (09-027-26) sees it on the CX-90/CX-70 PHEV, together with P0AB9, as a cold-weather no-READY caused by moisture at luggage-area connector 3002-411.

Likely causes

Software fault in the reporting or the B controller (updates released)
Water ingress or corroded terminals on the bus or relay connectors
Controller B not powered or not woken up in time
ECM/PCM B internally faulty

Symptoms

  • MIL or engine/drive system warning
  • No start or no READY on hybrids
  • Often no driveability complaint when the code is software-related

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€50–2,000
Time0.5–6 h

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

Parts involved

ecmcan bus wiring

Related codes

U0100U0101U0401U0073

References: saabwisonline.com, saabwisonline.com, static.nhtsa.gov, static.nhtsa.gov.