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 transmitting shift commands from the shifter to the transmission. A low voltage signal can disrupt communication, leading to erratic shifting or inability to shift gears. Common causes include a faulty gear shift control module, damaged wiring or connectors, a blown fuse, or a weak battery.
01. Most Common Causes
- Faulty gear shift control module
- Damaged or corroded wiring/connectors in the communication circuit
- Blown fuse or relay
- Weak battery or charging system issue
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in one gear or fails to shift
- No response from gear shifter
- Reduced fuel economy
03. 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 voltage with a multimeter; compare to manufacturer specs.
Step 4: Check fuses and relays related to the shift control module.
Step 5: If wiring and power are OK, replace the gear shift control module.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The vehicle may experience erratic shifting or become stuck in gear, posing a safety risk. Have it diagnosed promptly.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repair costs vary: a new shift control module can be $100-$300 plus labor, while wiring repairs are usually less.