The default code P138A is an OBD-II code specific to Ford, Lincoln, and Mercury vehicles. It indicates a problem related to the Variable Camshaft Timing (VCT) system or its control circuit, specifically concerning the VCT system’s oil pressure sensor. This fault can lead to a loss of performance, increased fuel consumption, and illumination of the check engine light (⚠️).
1. Meaning of Code P138A
- Official Definition:
* “P138A – VCT System Oil Pressure Sensor – Circuit ‘B’ Range/Performance.” *
This code signals an anomaly in the electrical circuit or operating range of the oil pressure sensor associated with the VCT system (typically on the “B” side of the engine, often corresponding to cylinders 2, 3, and 6). - Role of the VCT System:
The VCT system adjusts the camshaft’s advance or retard in real-time to optimize:- Power and torque.
- Energy efficiency.
- Reduction of polluting emissions.
2. Common Symptoms
- 🚨 Check engine light illuminated (MIL).
- ⚠️ Noticeable loss of power during acceleration.
- 🔥 Rough idle (engine shaking at idle).
- ⛽ Increased fuel consumption (up to 15-20%).
- 🐌 Delayed throttle response.
- ⚠️ Engine stalling or operation in degraded mode (“Limp Mode”).
3. Possible Causes
Here are the most frequent causes listed in order of probability:
| Order | Cause | Description |
|---|---|---|
| 1 | Oil level/pressure issue | Low level, aging oil, clogged oil filter, weak oil pump. |
| 2 | Faulty oil pressure sensor | Internal failure, damaged electrical circuit (wires, connectors). |
| 3 | VCT solenoid problem | Solenoid stuck (open/closed) or clogged by deposits. |
| 4 | Unsuitable engine oil | Incorrect viscosity (e.g., 5W-20 required but 10W-40 used). |
| 5 | Wiring/connector issue | Broken wires, oxidation, short circuits. |
| 6 | PCM module failure | Rare, but possible (faulty electronic management). |
4. Step-by-Step Diagnosis
Required Tools:
- OBD-II scanner (with advanced functions for Ford).
- Digital multimeter.
- Oil pressure gauge.
Steps:
- Check the oil level and condition:
- Check the level with the dipstick.
- If the oil is black or viscous, perform an oil change.
- Test the oil pressure:
- Use a pressure gauge (expected value: 20-80 PSI depending on RPM).
- Low pressure = pump/filter problem.
- Inspect the sensor and its circuit:
- Disconnect the sensor connector.
- Test the supply voltage (typically 5V or 12V).
- Check for continuity and absence of short circuits.
- Check the VCT solenoid:
- Measure the resistance (typical value: 5–15 Ω).
- Clean the solenoid with a specific degreaser.
- Analyze live data:
- With a scanner, compare the oil pressure sensor values with manufacturer specifications.
- Observe the status of the VCT solenoids (% activation).
5. Repair Solutions
- If oil degraded/low level:
➡️ Complete oil change + new filter + oil compliant with the manual (e.g., 5W-20). - Faulty sensor:
➡️ Replace the sensor (average cost: 80–150 €).
Affected models: Focus, Fiesta, Escape, Explorer (2010–2020). - Stuck VCT solenoid:
➡️ Clean or replace (cost: 100–250 €). - Damaged wiring:
➡️ Repair wires or replace the connector. - Persistent low oil pressure:
➡️ Check the oil pump or clogged filter.
6. Average Repair Costs
| Item | Part Price | Labor | Total |
|---|---|---|---|
| Oil pressure sensor | 80–150 € | 50–100 € | 130–250 € |
| VCT solenoid | 90–200 € | 100–150 € | 190–350 € |
| Complete oil change | 40–70 € | 30–50 € | 70–120 € |
7. Prevention
- ✅ Regular oil changes (follow the maintenance schedule).
- ✅ Use the recommended engine oil by Ford.
- ✅ Check the oil level monthly.
- ✅ Avoid repeated short trips (promotes clogging).
Conclusion
The P138A code on Ford vehicles is often related to a mechanical or electrical problem in the VCT system, generally easy to resolve if diagnosed early. Clean and suitable oil is the first lead to check. Ignoring this fault can damage the VCT system, leading to costly repairs (e.g., camshaft replacement). If in doubt, consult a Ford specialist mechanic equipped with appropriate diagnostic tools.