I have a renault laguna 2.2 dci with 122k on the clock it has started to blow clouds of black smoke out from the exhaust

Hi. From your description, I would advise starting by checking the EGR valve and it's housing. Remove the housing and EGR valve assembly and thoroughly clean them both with carb cleaner. It would be worthwhile taking the egr valve to your local Renault dealer who can also connect it to their EGR cleaning tool to check it's operation and clean the shaft thoroughly. The EGR valve may need replacing though, as they are prone to sticking. If this does not improve things, I would advise checking the air intake for blockages/leaks, and check the intercooler is not split. I would also advise checking the turbo shaft for excessive free play, and any signs of damage to the impeller. The fault code you mention is a strange one, and I would advise checking the powers and grounds to the injection computer when running, if these are ok, then if this trouble code keeps occuring, it may be the computer at fault. I hope this helps. Kind regards

Hi. The injection computer would flag an EGR valve fault if the movement from the potentiometer in it was outside it's mapped values, however it is possible that the valve can stick and be just inside these values and not flag a code. Also if the solenoid is operating following the computer outputs, but is not connected to the valve internally, this would mean that the valve could be stuck, and the solenoid would be working perfectly, and thus not reporting a fault. Also the housing on this engine is known for also getting large deposits of sludge build up and cause issues, I have also seen these crack slightly as well. The EGR valve should operate quickly and make a good seal on it's seat. A Renault dealer EGR valve tool can test for this, but again this cannot be tested under the engine operating conditions.
The voltage control to the injectors is carried out by the ecu. If you clear the code, and it returns with the fault, then a thorough check of the wiring to the ecu will be needed. You should check powers, grounds at the ecu with the engine runningto ensure these are good. I would advise a volt drop test of these also. If the code keeps on returning, and all wiring is good, then the ECU may well be the problem. You may be able to send it away for testing and repair by searching the internet for suitable companies. Overall, I would start by checking the air intake as menitoned previously, and remove the EGR housing and clean this thoroughly. One other area that can cause all kinds of issues, is to the right hand side of the battery, there are two large block connectors. These connections are very fine and can cause intermittant problems. I would advise removing them and clean with contact cleaner and then retry. If you also remove the battery, it's tray, you will gain access to the ecu. Check in this area for any signs of the harness rubbing through anywhere, as I have seen this happen on occasions. Kind regards.