Engine Warning Light

[marktheman]

Honda Civic Hatchback 1.6 Diesel 2015 - 117,000 miles

Over a year ago the EML came on and the car went into limp home. My garage said the code was showing a P0401. He put fuel cleaner additive in the tank, reset the code,  and told me to drive the car at a steady 4000 revs on the dual carriageway. This sorted the problem out for a month or two before the light came back on. He did the same as before and again this sorted the problem out for another month or two. On the third occasion he said that it is probably a sticking EGR valve but at £900 cost he decided to have the car in and clean the EGR. This time we took the car to Northern Ireland and drove about 800 miles on mostly motorways. No light came on for another 4 months. In the meantime I bought two Oilsyn Carboncode DPF and Turbo Doctor cans, using them over a couple of months. The light came back on and I went back to my mechanic. He said it was the same code but it was referring to the B EGR which is a low pressure EGR at the back of the engine (he didn't realise the car had two). He had the car in again and stripped and cleaned everything, he found a line with a filter in it which was heavily coked up. His invoice says "cleaned out the cooler and filter". Two months later and the light keeps coming on and very soon after a reset, always goes into limp home but an engine restart clears limp home for 20 miles or so. I've spent £500 so far and I really don't want to spend lots more on a car worth 3 or 4K px. What shall I do? Thank you

Edited August 21, 2023 by marktheman

[Trevor]

The long and short is that the engine is not being driven hard enough

When you mentioned that you did a long journey on a motorway and the light stayed off for some time then this is what needs to be done every so often to keep things clear.
Take a look at this post for further information:  

 

[marktheman]

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.

 

 

 

 

Edited August 23, 2023 by marktheman

[Trevor]

It all comes back to the one issue, the car is not suitable for short distance driving at low revs for a sustained period of time.
Once you have managed to clear out the DPF then run it at high revs for longer in lower gears and it should be fine

Better quality fuel may help but not entirely convinced 

Another issue that can occur from slow / low rev driving is that the turbo variable vanes can gum up with carbon deposits and although this can be cleaned with treatments that can be found on eBay it will occur every so often unless the carbon is not allowed to build up again