Vehicle: Renault Laguna II (Phase 2)
Year of manufacture: 2007 Engine: 1.9dCi (F9Q) Symptoms: Poor performance, DPF Warning light & “Injection Fault” message Fault codes: DF308, DF311 Duration: 2Hrs Customer Brief:The customer came to see us with this vehicle after it had been to several other garages who had tried (unsuccessfully) to clear the fault codes on generic diagnostic equipment with complaints of poor vehicle performance, a flashing DPF warning light and the generic message “Injection Fault” displayed on the vehicles multi-function display.
Initial investigation & rectifying the fault:DPF faults on modern diesels are commonly misdiagnosed especially on Renault vehicles as requiring the actual replacement of the DPF unit (Diesel Particulate Filter) which is not only an extremely costly exercise as the filters alone can cost over £800 but is in most cases not actually required. After a quick look at the vehicles live data parameters it was evident to us that the vehicle did indeed have a blockage within the DPF unit and could see that the vehicle had attempted (and failed) a total of ten times to automatically regenerate the system so a forced regeneration would be required (See below for more information on “Self regeneration” and “Forced regeneration”).
Your DPF is essentially a large kiln like oven which requires the exhaust gases flowing through it to bring it up to normal temperatures of over 400 degrees centigrade. This temperature allows it to burn up, upon entry, any soot particles that enter the filter and in return greatly reduces the visible black smoke that diesels of old are notorious for emitting. Blockages like this are normally caused by too many short “Start/Stop” journeys which stops the DPF achieving its normal operating temperature and instead of the soot burning off upon entry it blocks the fine mesh inside the particulate filter. This soot build up/blockage decreases the speeds of your vehicles exhaust gasses flowing through the filter creating a choke-point that makes the engines power output feel sluggish or slow.
After the forced regeneration was carried out the vehicle was allowed to run/cool down for an additional 10 minutes after which the engine was switched off and allowed to stand for a further 20 minutes. The engine oil was then changed and the vehicles DPF additives reset which removes the DF308, DF311 fault codes and extinguishes the the DPF warning light and removes the generic “Injection Fault” message.
DPF – “Self regeneration”:Normally, your vehicle will automatically detect minor blockages in the DPF by means of two pressure sensors in the exhaust gas stream and if it detects a minor blockage it will attempt to “Self-Regenerate”. For this to happen the engine management must detect some specific criteria has been met; mainly that your engine is at normal operating temperatures and that you’ve been travelling at a constant 50-70mph for the last ten minutes. This process normally occurs in the background without ever being noticed as you drive your vehicle but if the process is interrupted (Braking or dropping out of a constant cruise) it makes a note of the failed attempt and waits for the regeneration criteria to be met again. It will repeat this task up to a total of ten to twelve times (Vehicle/Engine platform dependent) where upon the final failed regeneration attempt the vehicles performance will be limited and a warning light/generic message will be displayed to the driver.
DPF – “Forced regeneration”:
When the automatic self regeneration process fails and the warning lights are displayed you have no choice but to take the vehicle to either a Renault main dealer or an independent specialist with the correct equipment (such as ourselves) that can force your vehicle to regenerate the diesel particulate filter. This process can take over 30minutes to perform and it automatically creates the perfect environment for the regeneration process to take place. Unfortunately the process also causes the engines temps and DPF temps to reach levels that wouldn’t normally be seen (The DPF and turbo can reach 800 Degrees Centigrade) which causes the engine oil to get so hot that the engine oil will need to be replaced afterwards and it is essential that this be done after the process has been carried out.
Renault Laguna II (Ph2) – 1.9DCi DPF Regeneration (DF308, DF311)