Meaning
P1394 Audi The engine control unit (ECU) detects that the actual position of the camshaft is too advanced compared to the position it expects, calculated based on the crankshaft position (TDC sensor).
In other words, the timing between the crankshaft rotation and the camshaft rotation is disrupted and exceeds the tolerance limits that the ECU can compensate for.
Probable Causes
Causes are divided into two categories: mechanical and electrical.
- Timing Belt/Chain Issue (The most common and serious cause):
- Timing belt/chain teeth skipping: This is the most frequent cause. The belt or chain has skipped one or more teeth due to a faulty tensioner, a loose (worn) belt, or a worn pulley.
- Incorrect timing belt installation: If the fault appears after work on the timing system, it is likely that the timing marks were not perfectly aligned.
- Electrical/Sensor Problems:
- Camshaft Position Sensor (CPS) failure: The sensor itself is faulty and sends an incorrect signal.
- Crankshaft Position Sensor (CKP) failure: If this reference sensor is faulty, the ECU can no longer calculate the timing correctly.
- Wiring harness issue: Cut wires, oxidized, loose, or corroded connectors linking the sensors to the ECU.
- Other Mechanical Problems:
- Variable Valve Timing (VVT) system failure: Although P1394 often points to mechanical timing, a variable timing system (e.g., Audi VVT system) stuck in an “advanced” position (due to a faulty solenoid or lack of oil) can also trigger this code.
- Tensioner or pulley problem: Wear preventing the correct tension of the belt/chain from being maintained.
Associated Symptoms
This fault causes very pronounced symptoms:
- Engine shaking violently at idle and low RPM.
- Hard starting or impossible to start.
- Significant power loss and very weak acceleration.
- Unstable idle with risk of stalling.
- Malfunction indicator lamp (orange warning light) illuminated.
- In severe cases, metallic knocking sounds can be heard (this is an absolute emergency!), indicating that the pistons are hitting the valves (interference engine).
Solutions and Diagnostic Procedure
IMPORTANT WARNING: Do not attempt to start or drive the vehicle for long distances. If the timing has jumped, you risk serious internal engine damage (bent valves, damaged pistons), leading to an extremely costly repair.
The logical procedure is as follows:
- Check the Timing System (ABSOLUTE PRIORITY): This is the first thing to do. It is essential to visually check the timing alignment by removing the timing cover(s) and aligning the crankshaft and camshaft marks. If the marks are not aligned, the timing has jumped.
- Reading Live Data: Using a capable diagnostic tool, read the values from the CPS and CKP sensors, as well as the variable timing commands to see if they are consistent.
- Check Sensors and Wiring:
- Visually inspect the connectors of the CPS and CKP sensors.
- Check the condition and output voltage of the sensors with a multimeter.
- Check for any broken or chafed wires.
- Check the Variable System (VVT): If the mechanical timing is correct, check the variable timing solenoid and the engine oil pressure.
Repair Cost
The cost depends entirely on the root cause:
- If timing belt/chain has skipped teeth: Requires replacement of the complete timing kit (belt/chain, tensioner, pulleys) + significant labor. High cost.
- If only a sensor is faulty: Moderate cost (part + labor).
- If internal engine damage (bent valves): Very high cost (engine disassembly, valve replacement, etc.).
Conclusion: For the P1394 code on an Audi, the first assumption should always be a timing system alignment problem. It is highly recommended to entrust the diagnosis and repair to a professional mechanic or an Audi specialist, equipped with the necessary tools and expertise.