Experiencing limp mode and a “17965 – Charge Pressure Control P1557 – 35-10 – Positive Deviation – Intermittent” error code on your 1.9TDI engine? This common issue, frequently diagnosed using VCDS (Vag-Com Diagnostic System) tools like Vcds 17965, indicates a problem with your turbo boost control system. Let’s explore potential causes and troubleshooting steps. This article specifically addresses this error on a stock 1.9TDI Octavia Mk1, 100PD, where the problem persisted even after replacing a loose boost hose.
Understanding VCDS 17965: Charge Pressure Deviation
The “Positive Deviation” in the fault code 17965 signifies that the actual boost pressure surpasses the requested boost pressure determined by the ECU (Engine Control Unit). This overboost condition triggers limp mode, a protective mechanism that limits engine power to prevent damage.
Troubleshooting Steps for VCDS 17965
Several components can contribute to this overboost issue. Here’s a breakdown of common culprits and how to investigate them using VCDS 17965 or similar diagnostic tools:
1. Verify the MAP Sensor
The Manifold Absolute Pressure (MAP) sensor measures the pressure in the intake manifold. A faulty MAP sensor can provide inaccurate readings, leading to incorrect boost control. Use VCDS to monitor the MAP sensor readings in Measuring Blocks. Compare the actual pressure with the specified pressure under various engine loads and RPMs. Significant discrepancies indicate a potential MAP sensor problem.
2. Inspect the N75 Valve
The N75 valve is a solenoid that regulates boost pressure by controlling the flow of vacuum to the turbocharger actuator. A malfunctioning N75 valve can cause overboost or underboost conditions. In VCDS, you can activate the N75 valve using the Output Tests function. A properly functioning valve should cause noticeable changes in engine RPM. No change or erratic behavior suggests a faulty N75 valve.
Example of VCDS logging in Block 011, showing data collected during a 3rd gear pull until limp mode was activated around 3000 RPM.
3. Check for Vacuum Leaks
Vacuum leaks in the boost control system can disrupt the delicate balance of pressure needed for proper turbo operation. Inspect all vacuum hoses, connections, and the intake manifold for leaks. A hissing sound or a noticeable drop in engine vacuum at idle can indicate a leak.
4. Investigate the Turbo Actuator
The turbo actuator controls the movement of the turbocharger vanes, which regulate boost pressure. A seized or sticky actuator can lead to overboost. Visually inspect the actuator rod for smooth movement. You can also use VCDS to monitor the specified and actual boost pressure while manually actuating the turbo. Any binding or resistance suggests a potential actuator issue.
Further Considerations
While a stuck EGR (Exhaust Gas Recirculation) valve might contribute to performance issues, it’s less likely to be the direct cause of the 17965 error. However, addressing any existing EGR problems is always recommended for optimal engine health.
Conclusion
Troubleshooting the VCDS 17965 error requires a systematic approach to identify the root cause. By utilizing the diagnostic capabilities of VCDS and carefully inspecting the components mentioned above, you can effectively diagnose and resolve the overboost condition, restoring your 1.9TDI engine to its full potential.
