Powertrain, generic · Transmission

P085A Gear Shift Control Module B Communication Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Gear shift control modules A and B are selector modules of shift-by-wire systems, such as Audi's selector lever J587 or Stellantis' rotary shift module. The codes cover a dedicated link to the gearbox module and the module's plausibility. If the selected range cannot be transferred reliably, the gearbox holds its range, goes to P at standstill or into limp mode. Modules on CAN report lost communication as U0103 or invalid data as U0404 instead; GM uses its own codes. P085A is the general fault of the link to module B: no or no valid frames. No maker documents it; California's rule requires missing communication of digital inputs to be stored separately.

Likely causes

Wire or connector between selector module and gearbox module: open, chafed, moisture in the console
Power or ground of the selector module
Software of selector or gearbox module
Selector module faulty

Symptoms

  • Selector or gearbox warning in the instrument cluster
  • Range cannot be selected or only with delay, car stays in P/N
  • Gearbox limp mode

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,500
Time0.5–3 h

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

Parts involved

electronic shift moduletransmission control moduleserial data linemodule wiring

Related codes

P085BP085CP085EP0860U0103U0404

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov.