Gear Shift Control Module Communication Circuit High
The P085C code indicates that the powertrain control module (PCM) has detected a high voltage condition in the communication circuit of the gear shift control module. This module is responsible for sending shift commands to the transmission. A high voltage reading typically points to a short to power, a faulty module, or wiring issues. This can disrupt communication between the PCM and the transmission, leading to erratic shifting or no shift response.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in one gear or fails to shift
- Erratic or harsh shifting
- Reduced fuel economy
2. Most Common Causes
- Short to battery voltage or ignition on the communication bus (CAN, LIN) or signal line of Shift Control Module 'B'
- Open circuit in the power supply or ground of Shift Control Module 'B', causing a high pull-up reading
- Damaged, corroded, or loose connector terminals at Shift Control Module 'B' or TCM
- Internal failure of Shift Control Module 'B'
- Internal failure of the TCM/PCM (signal receiver)
- Data network integrity issues (electrical noise, defective bus termination)
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the wiring and connectors for damage, corrosion, or loose connections.
Step 3: Use a multimeter to check for voltage in the communication circuit; compare to manufacturer specs.
Step 4: Test the gear shift control module per service manual procedures.
Step 5: If no issues found, clear code and test drive to see if it returns.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause unpredictable transmission behavior, potentially leading to a safety hazard or further transmission damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and minor repairs like cleaning connectors or replacing a fuse. Module replacement can be more expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.