Shift Solenoid Control Circuit Low Voltage
The P099B code indicates that the powertrain control module (PCM) has detected a low voltage condition in the control circuit of a specific shift solenoid. This solenoid is responsible for regulating hydraulic pressure to engage the correct gear. A low voltage reading suggests an electrical fault, such as a short to ground, open circuit, or failed solenoid, which can cause erratic shifting or transmission slippage.
01. Most Common Causes
- Faulty shift solenoid
- Short to ground in solenoid control circuit
- Open or damaged wiring/connector
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifting
- Transmission stuck in gear or limp mode
- Decreased fuel economy
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect wiring and connectors for damage or corrosion.
Step 3: Test solenoid resistance with a multimeter (compare to specs).
Step 4: Check for voltage at solenoid connector with ignition on.
Step 5: If wiring and solenoid are okay, test PCM output or replace PCM.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended as it can cause transmission damage or unsafe driving conditions. Limp mode may limit speed.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, but could be higher if the PCM needs replacement.