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1. Introduction
- Why intermittent codes are frustrating: high garage costs, risk of unexpected breakdown.
- Concrete example: A P0301 code (cylinder 1 misfire) that only appears when hot.
2. Common Causes of Intermittent Codes
- Worn wiring: Chafed or oxidized wires (e.g., camshaft sensor on Peugeot 308).
- Dirty connectors: Moisture or corrosion (common in older vehicles).
- End-of-life sensors: Oxygen sensor or pressure sensor failing intermittently.
- Electrical issues: Poor ground, weak battery, faulty alternator.
3. Essential Tools
- OBD2 scanner with recording function (e.g., BlueDriver, Autel MaxiScope): Captures real-time data.
- Smoke tester (e.g., OEM Tools 25600): Detects micro air or evaporation leaks.
- Multimeter with Min/Max function: Measures voltage variations on sensors.
- Portable oscilloscope (e.g., Hantek 1008C): Analyzes CAN Bus signals or injectors.
4. Diagnostic Methods
- Method 1: Recording data while driving
- Set up the scanner to record parameters (e.g., RPM, sensor voltage) during a drive.
- Identify correlations between codes and driving conditions (e.g., P0171 code during acceleration).
- Method 2: Simulating failure conditions
- Shake wiring harnesses with the engine running to reproduce an intermittent connection.
- Use a hairdryer to heat a suspect sensor (e.g., oxygen sensor).
- Method 3: Thorough visual inspection
- Check cable routes near hot parts (e.g., turbo) or moving components (steering, suspension).
5. Practical Cases
- Case 1: P0456 code (minor EVAP leak) on a Volkswagen Golf VII – Leak detected via smoke tester at the fuel cap.
- Case 2: Intermittent U0401 code (invalid ECM data) on a Renault Scénic – Problem solved by cleaning the engine control unit connectors.
6. FAQ
- “Can an intermittent code disappear on its own?”
Yes, but it remains stored in the ECU memory until cleared.
- “What cheap tool for beginners?”
The Creader 7021 or the Torque Pro app with an ELM327 adapter.
7. Mistakes to Avoid
- Clearing codes without diagnosing the cause.
- Neglecting electrical grounds (e.g., corroded ground cable on the chassis).
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