A faulty crankshaft position sensor is a common cause of intermittent starting problems and sudden engine stalling while driving in the 2003-2009 Renault Scenic. This sensor sends information about the crankshaft to the engine control unit, which ensures that the ignition and fuel supply are controlled correctly. If this component fails, the engine will no longer start or will cut out without warning. For owners of the Renault Scenic from this generation, it is important to recognise the typical symptoms and act quickly. Discover here why this problem is so difficult to diagnose and how you can resolve it easily.
Why the crankshaft position sensor is so important
The crankshaft position sensor measures the position and speed of the crankshaft. This information is sent directly to the Engine Control Unit (ECU), the engine’s computer. Without this signal, the computer cannot regulate the ignition and fuel supply at the right moment. The result is that the engine will not start, even if the starter motor is turning without issues. The sensor is a small component, but it plays a decisive role in the functioning of the engine.
In the Renault Scenic from this period, the sensor is supplied with two electrical connections. Different engine variants may have different versions. Therefore, always check the engine code and specifications before ordering a new sensor.
Typical symptoms of a failing crankshaft position sensor
Owners of the Scenic II regularly report that the problem occurs at unpredictable times. This makes diagnosis difficult. A sensor may still work temporarily and then suddenly fail, especially due to heat or vibration. These complaints are common with a faulty crankshaft position sensor:
- The starter motor turns, but the engine does not start
- The engine cuts out while driving without warning
- Starting problems occur mainly when the engine is warm
- The problem is intermittent: the car sometimes starts and sometimes does not
- There may be error codes in the engine management system, but that is not always the case
The intermittent nature of the symptoms causes many owners to investigate other causes first. This takes time and often leads to unnecessary frustration.
What makes diagnosing this problem so difficult
The intermittent nature of the fault makes it difficult to find the cause immediately. A sensor may work normally during diagnosis at the garage and fail again a few hours later. This is compounded by the fact that the symptoms are often heat-related. When the engine is cold, the car starts normally, but as soon as everything is up to temperature, the sensor fails.
Practical stories on car forums confirm this pattern. Owners describe situations in which the car no longer starts after a long journey, only to start again without problems after cooling down. This indicates a sensor that loses its function under heat or vibration.
How to identify a faulty sensor
For a proper diagnosis, it is wise to rule out other causes first. Check the battery, starter motor, fuses, relays, and fuel supply. If you suspect a problem with the crankshaft position sensor, pay attention to the following points:
- Connect a diagnostic tester and check whether a RPM signal is visible while starting
- Read any error codes that point to a missing crankshaft signal or synchronisation problems
- Inspect the plug and wiring of the sensor for damage or loose contacts
- Check the sensor itself for dirt or metal filings, which can interfere with the signal
A RPM signal that is missing during starting is a strong indication of a faulty crankshaft position sensor. This signal should be visible immediately once the starter motor turns the engine.
‘ Only replace the sensor if the wiring is in order and the diagnosis points to the sensor. ’
Replacement of the crankshaft position sensor
Replacing the sensor is not a complicated job. For the Renault Scenic II from the 2003-2009 period, the sensor is available as a separate part. The sensor is usually located on the engine side, often near the crankshaft or the flywheel. The exact position may vary depending on the engine variant.
When replacing, it is important to check the wiring and plug first. Cable breakage or rust in the connector can cause similar symptoms. Only replace the sensor if the wiring is in order and the diagnosis points to the sensor. When replacing, use a sensor that fits your engine code and check the number of electrical connections.
Practical tips for starting problems caused by sensor failure
Experienced owners and mechanics recommend following these steps if you suspect a faulty crankshaft position sensor:
- Always check the plug and wiring first before replacing the sensor
- Have error codes read immediately after a non-starting situation, as temporary faults can disappear after multiple starting attempts
- Replace the sensor preventively if the symptoms are clearly intermittent and diagnosis points to signal loss
- Beware of confusion with other problems such as a faulty fuel pump, ignition coils, or a starter relay, as these can produce similar symptoms
A crankshaft position sensor is relatively affordable and easy to replace. This makes it attractive to proceed to replacement immediately if there is a strong suspicion, especially if other causes have been ruled out.
What to look out for during maintenance
Although the crankshaft position sensor is normally maintenance-free, exposure to heat, vibration, and contamination can limit its lifespan. With older Scenics from this generation, it is wise not to rely solely on error codes. Intermittent faults are often caused by a sensor that is still just functioning but fails under load or temperature.
If the car starts poorly occasionally or cuts out suddenly, check the live RPM signal with a diagnostic tester. This provides immediate insight into whether the sensor is communicating correctly with the engine computer. Regularly checking the wiring and connectors also prevents a loose contact from being mistaken for a faulty sensor.
Checklist for owners of the Renault Scenic 2003-2009
Do you recognise one or more of the following situations? Then there is a good chance that you are dealing with a failing crankshaft position sensor:
- The car does not start, but the starter motor turns normally
- The engine cuts out occasionally while driving
- The problem occurs more often with a warm engine
- There is no clear cause after checking the battery and starting system
- The symptoms are intermittent and difficult to predict
In these cases, it is wise to have the sensor, plug, and cable harness checked by a mechanic or do it yourself with a diagnostic tester.
What this means for your Renault Scenic
A failing crankshaft position sensor is a known weakness in the Scenic II from the 2003-2009 model years. The problem is not always recognised immediately because the symptoms are intermittent and temperature-related. This makes targeted diagnosis important. Many owners lose time and money replacing other parts, while the cause lies in this small sensor.
Fortunately, replacing the sensor is simple and affordable. With the right diagnosis and a bit of technical insight, you can solve this problem yourself or go to a garage with the right information. This saves time and prevents unnecessary repairs.
On the Carnews website, you will find much more information about common car problems, maintenance tips, and practical advice for various car brands and models. Discover more about your car and stay well informed about potential problems and solutions.
Frequently asked questions
Typical symptoms are that the starter motor turns the engine, but the engine does not start, especially if the engine is warm. The car can suddenly cut out while driving and subsequently start poorly or not at all. The symptoms often occur intermittently: sometimes it starts normally, sometimes not at all. In the diagnosis, you usually see no RPM signal during starting and possibly error codes that point to a missing crankshaft signal.
The crankshaft position sensor is a known weak point in the Renault Scenic 2003–2009 because it is sensitive to heat, vibration, and contamination, which makes the signal to the ECU unreliable. This leads to intermittent symptoms such as difficult starting, sudden cutting out, or failure to start at all, especially with a warm engine. The faults are difficult to diagnose because they do not always give a clear error code and other causes are suspected. In addition, connector and cable harness problems around the sensor regularly play a role, making it a recurring weak point.
You can first visually check the plug and cable of the crankshaft position sensor for corrosion, breaks, or loose connections, and clean and securely fasten them. Then (preferably with a simple OBD2 scanner) check during starting whether an RPM signal is registered; if this is missing, the sensor is suspicious. With a multimeter, you can measure the resistance of the sensor and compare it with the factory value (found in workshop manuals or online forums for your engine type). If the wiring is in order, the resistance deviates, or no RPM signal appears during starting while the starter motor is turning well, there is a good chance that the sensor is faulty.
Replacing the crankshaft position sensor is usually doable for a handy DIYer with basic tools, provided you choose the correct engine variant and matching sensor. Important points are: good accessibility (sometimes difficult), disconnecting the battery, checking the plug and cable harness for corrosion or breakage, and respecting the correct torque for the bolt(s). Check beforehand via engine type or chassis number whether the sensor truly fits in terms of plug and specifications. After installation, it is wise to have error codes read and check if a stable RPM signal is present during starting.
Keep the plug and cable harness of the crankshaft position sensor clean, free of corrosion, and securely fastened, as poor contacts often cause faults. Ensure there is no oil or dirt accumulation around the sensor, as metal filings and contamination can interfere with the signal. In case of irregular starting problems, have the live RPM signal and the wiring checked in time so that early failure is detected. Consider preventive replacement at higher mileages if the sensor is known as a weak point for your engine type.