Shift Solenoid Control Circuit High Voltage
The P0999 code indicates that the powertrain control module (PCM) has detected a high voltage condition in the control circuit of one or more shift solenoids. This typically points to an electrical issue such as a short to voltage, faulty solenoid, or damaged wiring/connectors. The transmission may exhibit harsh or erratic shifting, limp mode, or fail to shift properly.
1. Symptoms You Will Notice
- Check Engine Light on
- Harsh or delayed shifts
- Transmission stuck in gear
- Reduced fuel economy
2. Most Common Causes
- Short to voltage in shift solenoid circuit
- Faulty shift solenoid
- Damaged wiring or connectors
- Faulty PCM
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect wiring and connectors for damage, corrosion, or shorts.
Step 3: Test shift solenoid resistance and compare to specs.
Step 4: Check for voltage at solenoid connector with key on.
Step 5: If wiring and solenoid are OK, test PCM output or replace PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended as the transmission may fail to shift properly, leading to unsafe driving conditions or further damage.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the solenoid, wiring, or PCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.