i work for a renault dealership and can confirm that tdc sensor is the most common cause of non starting on this particular model what happens is the sensor intermittantly fails to transmit a signal to the ecu which in turn prevents the spark plugs from sparking hence the engine not igniting the fuel and starting as it uses this particular sensor data as a sparking reference its situated above the gearbox at the back of the cylinder head, and is fixed by two 10mm boltsand a 2 pin connector however when you buy a new one from a renault dealer you have to buy an additional piece of wiring as the connector has been modified along with the wiring to prevent this fault re-occuring it'l probably set you back just over £50 for the two good luck!
S3LEE, March 2010
