P085A
Gear Shift Control Module B Communication Circuit
Transmission controls
Generic OBD-II
Medium
What it means
P085A means the car has lost reliable communication with gear-shift control module 'B' over its data circuit. Without that link the transmission may stop shifting properly or enter limp mode. The usual causes are wiring, connector corrosion, or a power/ground problem rather than a mechanical transmission failure. The engine still starts and runs.
Medium
Can I keep driving? Usually — but the transmission may drop into limp mode with limited or no shifting, so get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Transmission won't shift, or enters limp mode
- Delayed or erratic shifting
- Loss of communication with the shift control module
Common causes
Most likely first
- Wiring or connector fault on the module's communication (bus) circuitLikely
- Moisture, corrosion, or loose pins at the gear-shift module connectorCommon
- Poor power or ground to the shift control moduleCommon
- Faulty gear shift control module 'B'Less often
- Mismatched or incorrectly configured module — least likelyLess often
How to diagnose & fix
Work through it in order
- Scan for other communication/network codes to gauge the scope of the fault.
- Visually inspect the module connector and wiring; repair damaged, corroded, or wet connections.
- Check the module's power and ground circuits.
- Test the communication circuit for opens or shorts against wiring specs.
- Replace or reprogram the shift control module if confirmed faulty. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P085A?+
The engine still starts and runs, but the transmission may stop shifting properly or fall into limp mode. Have it checked soon, especially if shifting feels wrong.
Can I just clear P085A?+
It returns until the communication wiring, connector, or module fault is repaired.
Related codes
Often seen with P085A
Read & clear P085A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX