P1394 Buick – Camshaft Position Sensor (CMP)

P1394 Buick Camshaft Position (CMP) Sensor – Excessively Advanced Timing

Simple Explanation: The Engine Control Module (ECM) detects that the actual camshaft position is too advanced compared to the position it expects, calculated based on the crankshaft position sensor.

In summary, there is a timing issue between the rotation of the crankshaft and the camshaft.

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Common Causes on Buick (General Motors)

Buick (GM) engines have their specific weaknesses. The most frequent causes for this code are:

1. Timing Chain Problem (Very Common Cause on GM):
   • Timing chain stretching or wear: This is a very common cause on GM chain-driven engines. Over time and mileage, the chain can stretch and “jump” a tooth on the sprockets, shifting the timing.
   • Failed chain tensioner: The hydraulic tensioner can weaken (often due to insufficient oil pressure or wear), allowing the chain to become too loose and jump.
   • Worn or broken chain guide(s): The plastic guides can break over time, leading to poor chain guidance and misalignment.
2. Sensor and Wiring Issues:
   • Failed Camshaft Position Sensor (CMP): The sensor itself is faulty and sends an incorrect signal to the ECM.
   • Failed Crankshaft Position Sensor (CKP): If this “reference” sensor is faulty, all timing calculations are skewed.
   • Electrical connection problem: Loose, corroded, or oxidized connector on the CMP or CKP sensor. This is a simple and common cause to check first.
3. Variable Valve Timing (VVT) System Problem:
   • Faulty variable timing solenoid: If the solenoid controlling oil flow to the phaser is stuck or faulty, it can lock the timing in an advanced position.
   • Faulty camshaft phaser: The hydraulic mechanism (actuator) on the camshaft that adjusts timing may be internally worn or stuck.
4. Engine Oil Pressure Problem:
   • The VVT system and chain tensioners rely on good oil pressure. Insufficient pressure (dirty oil, low level, worn oil pump) can prevent the system from functioning correctly and cause this code.

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Associated Symptoms

When this code appears, you may notice:

• Engine shaking and rough idle.
• Hard starting (engine cranks but doesn’t start).
• Significant loss of power and poor acceleration.
• Increased fuel consumption.
• Check Engine Light on.
• In severe cases (if the chain has jumped significantly), metallic rattling may be heard – this is an absolute emergency (risk of engine damage).

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Diagnostic Steps and Solutions

WARNING: Avoid driving the vehicle if symptoms are severe (significant shaking, rattling). You risk serious engine damage.

1. Simple checks first:
   • Check engine oil level and condition. Low or very dirty oil is often the culprit.
   • Visually inspect the CMP sensor connector (usually located on the cylinder head) to see if it’s clean and properly connected.
2. Diagnosis with a scan tool:
   • A mechanic can use an advanced scanner to observe live data from the CMP and CKP sensors and see their synchronization in real-time. They can also test the VVT solenoid.
3. Mechanical inspection (most important):
   • If simple checks yield nothing, it’s necessary to mechanically check the timing belt/chain alignment. This requires setting the engine to Top Dead Center (TDC) and inspecting the alignment marks on the timing sprockets. This is a major job that often requires disassembling engine components.
4. Replacing faulty parts:
   • If it’s a sensor or solenoid: Relatively moderate cost.
   • If it’s the timing chain: This is a costly and complex repair involving replacing the complete timing kit (chain, tensioners, guides) and significant labor.

Conclusion: On a Buick, the P1394 code very often points to a mechanical problem related to timing chain wear or its components. It is highly recommended to entrust the diagnosis to an experienced mechanic with the appropriate tools to avoid even more costly repairs.