The fault code is a highly manufacturer-specific Diagnostic Trouble Code (DTC) that primarily points to an issue with the flywheel signal information (commonly labeled in technical databases as "Informazione Segnale Volano" or related to the crankshaft/clutch synchronization position ). When this code triggers, the Engine Control Unit (ECU) detects an anomaly or data mismatch between the vehicle's dual-clutch transmission (EDC) system, the crankshaft sensor, and the flywheel rotation pattern.
The mechanical component itself may have seized or failed internally.
The engine's computer relies on this continuous data stream to know exactly when to fire the spark plugs (in petrol engines) and when to inject fuel into each cylinder.
Locate the flywheel sensor, which is positioned near the junction where the engine block meets the transmission bell housing. Check the plastic connector for broken tabs or signs of green moisture corrosion. Ensure the wiring loom is routed cleanly away from hot exhaust components. Step 3: Remove and Clean the Flywheel Sensor
🛑 Because the ECU cannot instantly figure out which cylinder is on its compression stroke without a clear flywheel signal, the engine may crank for several seconds before starting.
However, the frightening reality is that P158b is often the "canary in the coal mine" for the infamous phenomenon. If the variable vanes seize in a closed or semi-closed position, the engine can suck in its own engine oil (via the turbo seals), burn it as fuel, and accelerate uncontrollably until it hydrolocks or explodes.
Diagnosing the P158B code requires a systematic approach to check both the component and the wiring.
When this code triggers, the driver will usually notice immediate, tangible changes in vehicle behavior. Because air regulation directly impacts combustion, look out for these telltale signs:
Difficulty restarting immediately (sometimes taking up to 10 seconds).
Connect a Renault-compatible diagnostic tool (such as Tool Immo Renault Can K Line or clip software) to read live engine data. Monitor the "Exhaust Gas Pressure" parameters with the engine off and while running. With the ignition on but the engine off, the sensor should read close to atmospheric pressure (approx. 1000 mbar). If it reads excessively high or zero, the sensor or its circuit is compromised. Step 2: Visual Inspection of Wires and Hoses
The Engine Control Module (ECM) sets this code when it detects that the actuator or sensor responsible for managing idle speed or exhaust pressure is operating outside its expected factory specifications. Renault (and Dacia) System: Powertrain / Idle Air Control Code Type: Manufacturer-Specific (P-Code) Common Symptoms of P158B