Vehicle: Renault Megane II
Year of manufacture: 2005
Engine: 1.6 16v (K4M-761)
Symptoms: Running issues & “Injection Fault” message
Fault codes: DF080, DF119
Duration: 2 Day
Customer Brief:
The customer came to see us with this vehicle after exhausting their options with other garages unable to resolve an issue with the camshaft sensor. The problem involved the vehicles Engine Management “MIL” light being on along with the generic “Injection Fault” warning message being displayed. The vehicle also made a metallic ratting noise at warm idle and used more fuel than normal.
Day 1:
The car was delivered to us so first things first, after which we carried out our initial hours diagnostic. This confirmed that there was indeed a fault present with the camshaft sensor but as previous garages had already swapped the sensor out several times (with cheap, non-genuine parts before finally fitting a genuine item) we knew the sensor itself was unlikely to be the actual issue. From here we launched straight in to some basic conformity checks which look specifically at the sensor circuit so lets start with the basic supply… is the sensor getting any power? In this specific case the sensor was indeed receiving +12v from the UPC’s after ignition relay which ruled out a fault in this specific area so next up were the links between the sensor and the ECU itself (which requires the removal of the vehicles battery and battery box).
Megane II UPC
There are two wires from the camshaft position sensor which run directly to the ECU and they are the sensor earth and the sensor signal. The camshaft sensor is susceptible to electric noise interference so any damage to the physical wiring which isn’t detected in a continuity test can cause problems. Again, this wiring also appeared fine so the next port of call was to use an oscilloscope to see what the sensors were actually seeing and sending back to the ECU. Firstly we “scoped” the crankshaft sensor and then on a second channel we did the same to the crankshaft sensor. Both waveforms looked perfectly normal but when they were overlaid there was an obvious problem with the “synchronisation” of the sensor outputs so the engines timing was checked… The problem! The customer was informed and authorisation to proceed was obtained.
Megane II – K4M Timing belt
Day 2:
The vehicles timing was physically inspected and this confirmed what the previous days scope session had shown, incorrect “timing”, but to perform the reset job correctly requires some critical parts to be replaced, namely the timing belt kit, water pump, some oil seals, the camshaft/crankshaft fixings and the aux belt kit. The customer also requested that the dephaser pulley be changed as they are a common cause of problems on these particular engines so this part was added to the shopping list. After installing these new parts the vehicles engine was re-timed, reassembled, given a quick oil and filter change (Recommended after the installation of a new dephaser pulley unit on all VVC engines in the Renault range) and then restarted. Immediately the error codes were no longer showing as present and and once normal operating temperature was achieved the VVC mechanism could be seen to be working correctly in diagnostics. The audible “rattle” at warm idle was also no longer present which was another encouraging sign before finally taking the vehicle on a road test. Data logging confirmed that the VVC mechanism was working correctly and more importantly, the vehicle returned an average of 42mpg on the extensive road test.
The vehicle was handed back to the customer later that day.