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 can be caused by a short to voltage, a faulty solenoid, or an internal PCM issue. The transmission may exhibit harsh shifting, slipping, or fail to shift properly.
01. Most Common Causes
- Short to voltage in the shift solenoid circuit
- Faulty shift solenoid
- Damaged wiring or connectors
- Failed PCM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission slipping
- Vehicle stuck in limp mode
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Inspect the transmission wiring and connectors for damage, corrosion, or shorts.
Step 3: Test the shift solenoid resistance and compare to manufacturer specifications.
Step 4: Check for voltage at the solenoid connector with the ignition on; if voltage is high, repair the short.
Step 5: If all else fails, replace the PCM after verifying all other components.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause transmission damage or unsafe driving conditions.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on the cause and labor rates.