A 2017 Jetta is experiencing a recurring misfire on cylinder 1, despite recently replacing the spark plugs and ignition coil. This article analyzes a VCDS autoscan to diagnose the potential cause and suggests next steps for troubleshooting.
VCDS Autoscan Results and Analysis
A recent VCDS scan reveals the following fault codes related to the misfire:
- 10203 – Random/Multiple Cylinder Misfire Detected (P0300): This indicates a general misfire occurring across multiple cylinders, suggesting a potential issue affecting the entire engine.
- 10591 – Cylinder 1 Misfire Detected (P0301): This confirms the primary concern, pinpointing cylinder 1 as the source of the misfire.
- 33835 – Misfire Detected — Fueling Disabled (P0363): This signifies that the engine control module (ECM) has disabled fuel injection to the affected cylinder to prevent further damage. This often occurs when a misfire is severe or persistent.
The freeze frame data associated with these codes provides valuable insights:
- High Engine Load and RPM: The misfire occurred under load conditions (92.5-93.7% normed load value) and at higher engine speeds (2966-4183 RPM). This suggests the issue may be more pronounced when the engine is working harder.
- Consistent Operating Temperatures: Coolant and intake air temperatures were within normal operating ranges, ruling out overheating or excessively cold air as contributing factors.
Beyond the misfire codes, the autoscan also flagged a few unrelated faults:
- 03984 – Left Front Heated Seat: Open circuit, likely a wiring issue or faulty heating element within the seat.
- 01499 – Bulb for High-Beams; Right (M32): Open or short circuit, indicating a burned-out or malfunctioning high beam bulb.
- 01044 – Control Module Incorrectly Coded: This suggests a potential coding issue within one of the modules, requiring further investigation. This could be unrelated to the misfire.
- 0020 – Tuner for Satellite Radio B11CF: Deactivated, likely due to a subscription issue or a problem with the satellite radio tuner itself.
Troubleshooting Next Steps
Given the persistent cylinder 1 misfire despite a new coil, the following steps are recommended:
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Swap Ignition Coils: Swap the ignition coil on cylinder 1 with a known good coil from another cylinder (e.g., cylinder 2 or 3). If the misfire follows the coil, the coil is faulty, even if new. If the misfire remains on cylinder 1, the problem lies elsewhere.
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Inspect Wiring and Connectors: Carefully examine the wiring harness and connectors for cylinder 1’s ignition coil and fuel injector for any damage, corrosion, or loose connections. A poor connection can intermittently disrupt the spark or fuel delivery.
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Check Fuel Injector: Though less likely given the new spark plugs and recent successful operation, a faulty fuel injector on cylinder 1 could be contributing to the misfire. Consider testing the injector’s resistance and spray pattern.
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Compression Test: Perform a compression test on all cylinders to assess the engine’s overall health and rule out mechanical issues like a burnt valve or damaged piston rings in cylinder 1. Low compression in cylinder 1 would point to a mechanical problem.
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Further Diagnostics with VCDS: If the above steps don’t pinpoint the cause, more advanced diagnostics with VCDS may be necessary. This could include checking fuel pressure, measuring injector pulse width, and monitoring misfire counts in real-time.
Conclusion
A recurring cylinder 1 misfire in a 2017 Jetta, even after replacing the ignition coil, requires a systematic diagnostic approach. Using VCDS and following the recommended troubleshooting steps can help identify the root cause, whether it’s a faulty component, wiring issue, or a more serious mechanical problem. Addressing the unrelated fault codes is also recommended for optimal vehicle performance and safety.
