Shift Solenoid Control Circuit High Voltage
The P099C code indicates that the powertrain control module (PCM) has detected a high voltage condition in the control circuit of a specific shift solenoid. This solenoid is responsible for directing transmission fluid to engage the appropriate gear. A high voltage reading suggests a short to power, a faulty solenoid, or an issue with the PCM. This can cause erratic shifting, transmission slippage, or failure to shift, potentially leading to transmission damage if ignored.
01. Most Common Causes
- Short to power in the solenoid control circuit
- Faulty shift solenoid
- Damaged wiring or connector
- Faulty PCM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic or harsh shifting
- Transmission stuck in gear
- Decreased fuel economy
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional transmission codes.
Step 2: Visually inspect the transmission wiring harness and connectors for damage, corrosion, or loose connections.
Step 3: Test the shift solenoid resistance with a multimeter and compare to manufacturer specifications.
Step 4: Check for voltage at the solenoid connector with the ignition on; if voltage is higher than specified, repair short to power.
Step 5: If wiring and solenoid are okay, suspect a faulty PCM and perform further diagnostics.
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. Have the vehicle inspected immediately.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on the cause. Solenoid replacement is around $150-$250, while PCM replacement can exceed $400.