Gear Shift Control Module Communication Circuit Failure
The P085A code indicates a communication failure between the gear shift control module and other vehicle control modules, typically the powertrain control module (PCM) or transmission control module (TCM). This can be caused by a faulty gear shift control module, damaged wiring or connectors in the communication circuit, or a low battery voltage affecting module operation. The issue may prevent the transmission from shifting properly or cause the vehicle to enter a fail-safe mode.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in one gear or limp mode
- Inability to shift gears manually
- Erratic shift behavior or delayed engagement
2. Most Common Causes
- Faulty gear shift control module
- Open or shorted communication circuit wiring
- Corroded or loose connectors in the CAN bus
- Low battery voltage or charging system issue
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect the gear shift control module connector for corrosion, damage, or loose pins.
Step 3: Test the communication circuit (CAN bus) for continuity, shorts, and proper voltage.
Step 4: Verify battery voltage and charging system output; recharge or replace battery if low.
Step 5: If wiring and power are OK, replace the gear shift control module and reprogram if necessary.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as the transmission may fail to shift properly, leading to unsafe driving conditions or further damage.
How much does it cost to fix?▼
The cost typically ranges from $100 to $300, including diagnostic time and parts. Module replacement can be higher if reprogramming is required.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.