Gear Shift Control Module Communication Circuit Low
The P085B code indicates that the powertrain control module (PCM) has detected a low voltage condition in the communication circuit of the gear shift control module. This module is responsible for sending shift commands to the transmission. A low voltage signal can prevent proper communication, leading to transmission shifting issues or failure to shift. Common causes include a faulty gear shift control module, damaged wiring or connectors, or a blown fuse.
1. Symptoms You Will Notice
- Transmission fails to shift or shifts erratically
- Check Engine Light illuminated
- Vehicle stuck in one gear (limp mode)
2. Most Common Causes
- Short to ground in the communication circuit wiring
- Corroded or damaged pins in the gear shift module connector
- Faulty gear shift control module (B)
- Electrical issue in the transmission control module (TCM) or powertrain control module (PCM)
- Blown fuse or power supply problem to the shift module
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the gear shift control module wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the communication circuit voltage with a multimeter; compare to manufacturer specifications.
Step 4: Check the fuse for the gear shift control module and replace if blown.
Step 5: If wiring and fuses are okay, replace the gear shift control module.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The vehicle may enter limp mode, limiting speed and transmission function, which can be dangerous in traffic.
How much does it cost to fix?▼
Typical repair costs range from $50 to $150 for parts and labor, depending on the cause and vehicle model.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.