Error Code P085D is defined as Gear Shift Control Module ‘A’ Performance. This is a generic trouble code, meaning it applies to vehicles equipped with the OBD-II system, particularly those made from 1996 up to the present. It is also more common among specific vehicle makes, namely Audi, Citroen, Chevrolet, Hyundai, Ford, Nissan, Peugeot, and VW. Specifications on the definition, troubleshooting, and repairs vary from make, model, and powertrain configuration.
Both the Powertrain Control Module (PCM) and the Transmission Control Module (TCM) depend on various sensors to decide on the speed and torque to decide which gear to shift into. Thus, if these sensors experience problems, the vehicle’s drivability will suffer. This error code appears when the gear shift control module is defective and affects the ignition and exhaust system components.
- Hard shifts or gear slipping
- Lack of engine power
- Engine hesitates during acceleration
- Defective gear-related shift solenoid
- Defective gear-related gear or clutch pack
- Faulty engine coolant temperature sensor
- Faulty valve body
- Dirty transmission fluid (restricts hydraulic passage)
- Mechanical failure of the exhaust system or ignition system
- Broken or damaged wires, corroded connectors
- Failed PCM/TCM (rare)
How to Check
To diagnose this code, make sure to check all the wirings, connector, and associated components with the transmission system. Look for any signs of faulty or loose wiring and damaged or corroded connectors or components. Repair or replace as needed.
Next, use the PCM scanner to save the freeze frame data, especially the stored error codes on the PCM. Make sure to clear the codes before taking the vehicle for a test drive and see if the code returns.
If the error code returns, then check the individual auto transmission connector to see if there’s a reference voltage or ground signal present.
Check the condition of the transmission fluid, look for signs of abnormal smell such as burnt fluid. This can be indicative of damaged transmission caused by the low fluid condition. If that’s the case, remove the transmission pan and check for clutch pieces or other debris.
Fill the transmission fluid if it’s too low. This can also help you detect any leaks. Repair leaks as soon as possible. After filling leaks, make sure you fill the transmission fluid at the appropriate level.
Next, clear the codes and allow the vehicle to reach normal operating temperature before taking it for a test drive. See if the error code returns.
If the code comes back and the transmission is hesitating or slipping, then connect the manual pressure gauge. Use the manual pressure gauge along with the hydraulic pressure diagram. Check the transmission hydraulic pump for pressure. Compare your findings to the specifications set by the manufacturer.
If the pump is ok, but the problem persists, then use a digital volt/ohmmeter (DVOM) to test the shift solenoid for reference voltage and ground signal. Check for continuity; prevent memory loss by disconnecting any related control modules.
Test all related circuits for continuity and resistance. Refer to the manufacturer’s wiring diagram. Compare your findings with the specifications set by the manufacturer. If they check out, then they’re in good condition.
If the code persists, then consider checking the PCM. Clear the codes and retest the system to see if the code returns.
How to Fix
- For damaged transmission caused by the low fluid condition, the transmission must be rebuilt. Perform a fluid flush and replace the torque converter as well.
- Check for faulty wirings and damages on the connectors
- Repair any leaks in the transmission (if the transmission fluid looks good and only low)
- Replace damaged hydraulic pump
- Repair or replace damaged connectors or circuits
- Replace defective solenoid or solenoid pack
- Replace PCM (rare)
This code is a serious problem, which means it must be addressed as soon as possible. Also, you’re better off taking your vehicle to a qualified technician to address this code.