Shift Solenoid Control Circuit Low
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 a short to ground, open circuit, or faulty solenoid, which can cause erratic shifting or transmission slippage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifting
- Transmission stuck in gear or limp mode
- Decreased fuel economy
2. Most Common Causes
- Faulty shift solenoid 'G' with internal resistance out of specification
- Short to ground in the shift solenoid 'G' control circuit wiring
- Open circuit or corroded/loose connectors in the transmission wiring harness
- Low or degraded automatic transmission fluid (ATF)
- Defective solenoid block assembly
- Internal failure in the transmission control module (TCM) or powertrain control module (PCM)
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect transmission fluid level and condition.
Step 3: Visually check wiring and connectors for damage or corrosion.
Step 4: Test solenoid resistance with a multimeter (compare to specs).
Step 5: Check for shorts to ground or power in the control circuit.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a low control circuit can cause erratic shifting, transmission damage, or sudden loss of drive. Have it diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $50 to $150 for DIY solenoid replacement, or $200-$500 at a shop including labor and diagnostics.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.