P085B code meaning
Gear Shift Control Module B Communication Circuit Low
Powertrain system Generic code P08xx codes Check engine light
What P085B means
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. P085B means the link to module B stays at a low level, typically a short to ground or a sender that no longer releases the line. No maker documents it.
P085B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P085B
- Selector or gearbox warning in the instrument cluster
- Range cannot be selected or only with delay, car stays in P/N
- Gearbox limp mode
Common causes of P085B
- Most likelyCommunication line shorted to ground
- PossiblePower or ground of the selector module
- PossibleSoftware of selector or gearbox module
- PossibleSelector module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Electronic shift moduleTransmission control moduleSerial data lineModule wiring
What each part of P085B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 5B | The exact fault in that area. |
What to do next
- Note P085B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P085B
What does P085B mean?
P085B means "Gear Shift Control Module B Communication Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P085B?
Drive gently and only to a workshop. With P085B the car can go into limp mode (reduced power) to protect itself.
Will P085B fail an emissions test?
Yes, it can. P085B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P085B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P085B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.