Thank you Trevor. My daughter uses this on a 12 mile return journey each day with the return part being mostly in slow traffic. I think we will swap our petrol Hyundai with the Civic and drive it as you suggest. Should I put more cleaner in and should I be buying the Ultra Diesel fuel?
Also, if this doesn't fix the problem would an ECU remapping company be worth approaching, a local one says this,
"If you would like to avoid the excessive cost of DPF replacements we offer a full and effective DPF removal and ECU remap service for Bosch Siemens Denso!!! and Marelli.
After all The Diesel Particle Filter can be removed from vehicle. You won’t get any warning lights on the dash, limp mode or any expensive problems in the future. Unlike many other companies,after ECU/DPF custom remap process takes place, we perform a full diagnostic scan to check that the vehicle is in a fully working condition and has no faults or error codes present."
Alternatively, Oilsyn said,
If the EGR was cleaned then I doubt it is an EGR blockage issue, unless the Technician failed to clean the entire system from the EGR to the air intake.
How accessible is the EGR? Ideally, all pipework, vacuum hoses and EGR should be inspected again before it is replaced because not all P0401 codes mean the EGR is faulty. The ECU is detecting an airflow variance/discrepancy in the air intake system. Carbon on surface areas in the EGR is normal, whereas heavy build-up is not. If the EGR doesn't appear blocked, then I would check the EGR function to ensure the EGR is not sticking using the procedure below. If that is fine, have the MAP sensor checked with a diagnostic tool.
The below is from Honda:
1) Reset the ECM/PCM
to do this you need to pull a fuse under the hood. Its the No. 6 ECU 15A
pull this fuse for 15 seconds and then reinsert it
2) Go for a test drive under the following conditions
No electrical load, Im assuming they mean no headlights, radio, etc etc
and decelerate from 55 mph for at least 5 seconds
3) Check for a temporary DTC with the HDS or a scan tool
Is Temperorary DTC P0401 indicated?
YES-Clean the intake manifold EGR port with throttle body/intake cleaner. Also clean the passage inside the EGR valve with throttle body/intake cleaner, or replace the EGR valve.
NO-Intermittent failure, go to step 4
4) Turn the ignition switch off
5) Disconnect the EGR valve 6P connector
6) Connect the battery positive terminal to EGR valve connector terminal No 4
7) Start the engine and let it idle, then connect the battery negative terminal to terminal No 6.
Did the engine stall or run rough?
YES-Intermittent failure, system is OK at this time
NO-Clean the intake manifold EGR port with throttle body/intake cleaner. Also clean the passage inside the EGR valve with throttle body/intake cleaner, or replace the EGR valve.