P078D - Shift Timing Solenoid B High
The P078D code indicates that the Powertrain Control Module (PCM) has detected a high voltage or resistance condition in the circuit of Shift Timing Solenoid B. This solenoid is responsible for controlling hydraulic pressure to adjust shift timing in the transmission. A high signal suggests an electrical fault such as a short to voltage, open circuit, or a faulty solenoid, which can lead to harsh or delayed shifts.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Delayed gear engagement
- Transmission stuck in limp mode
- Decreased fuel economy
2. Most Common Causes
- Faulty shift timing solenoid B
- Short to voltage in solenoid circuit
- Open or high resistance in wiring/connectors
- Corroded or damaged electrical connectors
- Faulty PCM (rare)
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 loose connections.
Step 3: Test solenoid resistance with a multimeter (compare to specs).
Step 4: Check for voltage at solenoid connector with key on (should be battery voltage).
Step 5: If wiring and solenoid are good, test PCM output or replace PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause transmission damage. Limp mode may limit speed and gear selection.
How much does it cost to fix?▼
Repair costs typically range from $50 to $150 for DIY solenoid replacement, or up to $400 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.