Understanding and Resolving the P001685 Engine Code

The P001685 engine code indicates a problem with the camshaft timing. While this code isn’t specifically defined in generic OBD-II documentation, it’s often associated with Mercedes-Benz vehicles equipped with the M274 engine. This article outlines a potential cause of the P001685 code, specifically focusing on a slipped timing ring on the intake camshaft, and provides a comprehensive guide to replacing the camshaft adjusters.

Possible Cause: Slipped Timing Ring on Intake Camshaft

In the M274 engine, the P001685 code can be triggered by a shifted timing ring on the intake camshaft. Unlike some other Mercedes models, manually repositioning the ring isn’t feasible on the M274. This issue often manifests as a long crank time before the engine starts, accompanied by the P001685 code. Noises are typically not present with this specific problem. The solution involves replacing the intake camshaft. Although the intake and exhaust camshafts might appear identical, confirming the correct part number with a local Mercedes-Benz dealer is crucial. The intake camshaft part number for the M274 engine is 274-050-32-00.

Replacing Camshaft Adjusters: A Step-by-Step Guide

Replacing the camshaft adjusters on an M274 engine is a complex procedure that requires specialized tools and careful attention to detail. The following steps outline the process:

Preparation and Initial Disassembly

1. Crank Position: Rotate the engine to 79 degrees after top dead center (TDC) on cylinder 1 to avoid damaging the high-pressure fuel pump (HPFP). You’ll return the crank to TDC later.
2. Fuel System: Disconnect fuel lines from the HPFP to the fuel rail and carefully remove the HPFP.
3. Fuel Rail and Injectors: Remove the high-pressure fuel rail and fuel injectors.
4. Spark Plugs and Coils: Remove spark plugs and ignition coils for easier crank rotation.
5. Intercooler Lines: Disconnect intercooler lines from the top of the engine.
6. Wiring Harness: Disconnect and remove the engine wiring harness.
7. Valve Cover: Remove the valve cover.
8. TDC Adjustment: Rotate the engine to TDC on cylinder 1. This is critical for accurate timing.

Timing Tool Installation and Camshaft Adjuster Replacement

9. Timing Tool: Acquire a specific M274 engine timing tool set. Install the tool onto the camshafts, ensuring it fits correctly and confirming TDC on cylinder 1. Secure the tool in place.
10. Tensioner and Guide Rail: Remove the timing chain tensioner. Consider replacing the left timing chain guide rail while it’s accessible.
11. Chain Tension: Maintain tension on the timing chain using a zip tie or with assistance from another person. Prevent slack or disengagement from the crank gear.
12. Camshaft Adjuster Removal: Using the T100 camshaft adjuster socket from the timing tool set, carefully and gradually loosen the torque on the camshaft adjusters. Avoid excessive force.
13. Adjuster Replacement: Remove and replace one camshaft adjuster at a time. Do not remove both simultaneously.
14. Initial Tightening: Tighten the T100 valve controls on the new adjusters, but do not torque them to specification yet.

Timing Verification and Reassembly

15. Timing Tool Removal and Rotation: Remove the timing tool and rotate the crankshaft two full rotations. The TDC mark (O|T) should align after two rotations. Reinstall the timing tool and verify camshaft timing against the TDC mark.
16. Tensioner and Torque: Install the new timing chain tensioner and torque it to specification. Torque the T100 valve controls on the camshaft adjusters to specification.
17. Final Timing Check: Remove the timing tool and perform a final TDC/timing verification by rotating the crank two full rotations.
18. Reassembly: Reassemble all components in reverse order, remembering to return the crank to 79 degrees after TDC before reinstalling the HPFP.

Conclusion

Addressing the P001685 code likely involves replacing the intake camshaft due to a slipped timing ring. This guide provides a detailed procedure for replacing the camshaft adjusters, a crucial step in resolving this issue. Remember that this is a complex procedure requiring specific tools and expertise. Consult a qualified mechanic if you are not comfortable performing this repair yourself.