P0402 EGR & Lexia - Help Please

[cancunia]

I have a '05 Berlingo 2.0 HDi that has thrown up P0402 two times that I know of in the past 2 weeks and probably a third time back in August. Same symptoms each time, engine won't rev past 2750, no boost but no EML or other warning lights. The first & last time, the engine revs & boost came back on after a couple of hours & a few starts, the time in between I cleared the fault code via Lexia. Most impressively the problem cleared itself while I was driving on the last occasion.

From what I've read, P0402 means 'excessive' exhaust gas re circulation, so does that mean the EGR valve is open too much? Lexia, very (un) helpfully says 'incorrect' flow which is why I'm unsure.
I've checked the EGR valve by taking off the vacuum hose whit the engine at idle and can hear it click shut, so am assuming the EGR valve is working at least to some extent. I did some testing via Lexia, which tells me the EGR solenoid is faulty so that's a high possibility of the cause of the problem but I have some questions that I hoped could be answered in the mean time.

1, Should the EGR be open at idle speeds?

On the attached Lexia screenshot:

2, Does the Airflow Reference Value means that's what the ECU is expecting the airflow to be, vs what the reading is from Measured Air Flow?
3, What do the 2 EGR values mean:
EGR valve OCR?
EGR throttle electrovalve OCR?

On the attached screenshot the EGR values are the same at 10% but yesterday the electrovalve reading stayed at 10% while the other EGR valve reading changed according to engine speed. When the screenshot was taken, the engine was stopped.

Many thanks

[EDC5]

1. Yes, but only sometimes from my experimentation

2. Yes, reference value is what is stored in the map for that RPM etc.

3. The two EGR values are the EGR vacuum solenoid valve opening percentage and.... I think the EGR throttle may relate to the Doseur open percentage, although I'm not sure on that one, details here if you're interested: viewtopic.php?f=3&t=58705

Measured air flow is the reading from the MAF sensor. If the EGR is stuck open then you would expect to see the 'Measured air flow' lower than the 'Reference air flow' and if the EGR was stuck shut you would expect the opposite.

[cancunia]

Thanks for the info, it all makes sense as the EGR throttlevalve reading has never been anything other than 10%.
The fault happened again today while going to the shops. It was fine when I set off, but after a stop of about 15 mins, the fault returned. Checking with my OBD reader it showed P0402, I took the hose off from the EGR and got P0400 as well. I cleared the P0402 and drove home without bother.
When I was home, I took the EGR solenoid apart, nothing much to see inside apart from a diaphragm and a couple of springs. I gave it a clean & a shake then put it back together & back on the engine. Not exactly sure why, but now the EGR solenoid actuator test is working which was not the case yesterday.
I'm now constantly getting 10% on both EGR readings with the engine running and the airflow readings match, not yet done any miles to see what happens.
If the fault returns, I'm thinking it'll mean a new EGR solenoid rather than simply blanking or disconnecting the EGR as my ECU seems very sensitive to airflow mismatches. Maybe I'll go for a modded ECU instead.

[EDC5]

Thanks for the info, it all makes sense as the EGR throttlevalve reading has never been anything other than 10%.
The fault happened again today while going to the shops. It was fine when I set off, but after a stop of about 15 mins, the fault returned. Checking with my OBD reader it showed P0402, I took the hose off from the EGR and got P0400 as well. I cleared the P0402 and drove home without bother.
When I was home, I took the EGR solenoid apart, nothing much to see inside apart from a diaphragm and a couple of springs. I gave it a clean & a shake then put it back together & back on the engine. Not exactly sure why, but now the EGR solenoid actuator test is working which was not the case yesterday.
I'm now constantly getting 10% on both EGR readings with the engine running and the airflow readings match, not yet done any miles to see what happens.
If the fault returns, I'm thinking it'll mean a new EGR solenoid rather than simply blanking or disconnecting the EGR as my ECU seems very sensitive to airflow mismatches. Maybe I'll go for a modded ECU instead.

Yeah, I doubt if the EGR throttle (doeseur) would want to restrict the engine inlet too much in the name of EGR.

Any update on this?

By EGR solenoid do you mean the vacuum solenoid?

[cancunia]

Yeah, I doubt if the EGR throttle (doeseur) would want to restrict the engine inlet too much in the name of EGR.

Any update on this?

By EGR solenoid do you mean the vacuum solenoid?

Yep, the 'EGR solenoid' is the vacuum solenoid that controls the EGR, my engine does not have AFAIK the doesur valve so I'm guessing the 10% value is a minimum.
Since dismantling the solenoid, the fault has gone from daily P0402 to almost constant P0400 so I've ordered another via the bay. I bought 2 used solenoids from the same seller in the hope that one of them will work. If not, I'll send them back and buy a new one.

[EDC5]

Yeah, I doubt if the EGR throttle (doeseur) would want to restrict the engine inlet too much in the name of EGR.

Any update on this?

By EGR solenoid do you mean the vacuum solenoid?

Yep, the 'EGR solenoid' is the vacuum solenoid that controls the EGR, my engine does not have AFAIK the doesur valve so I'm guessing the 10% value is a minimum.
Since dismantling the solenoid, the fault has gone from daily P0402 to almost constant P0400 so I've ordered another via the bay. I bought 2 used solenoids from the same seller in the hope that one of them will work. If not, I'll send them back and buy a new one.

Thats interesting re the doseur, would you be able to check that by taking off the air pipe to the manifold to check?

So on my engine I have 3 vacuum control solenoids:

EGR
Doseur
Variable geometry turbo

Of these only the EGR has a feedback sensor to ensure it's working. I assume the operation of the Variable Turbo is monitored by the manifold pressure sensor against the map of known expected pressure. I'm not sure how the doseur is monitored, maybe indirectly with the MAF?

I've seen a video where someone cleans their Vacuum solenoid so I might be tempted to give that a go if they do indeed become blocked over time.



I'm assuming the solenoid valves for the EGR are similar?

[cancunia]

On my Berlingo, there's only the MAF on the intake, I think the doseur may only be on engines with an intercooler but may be wrong about that. I've had the EGR solenoid valve apart, found some grit inside which I cleaned out, put it back together and it's now very unhappy. It was probably on it's way out before I started as I got faults with increasing regularity.
On the Berlingo, there's no direct feedback from the EGR, so I think the way the EGR is measured is via the MAF. More EGR means less air expected by the MAF, too much or too little air through the MAF will assume incorrect EGR. Not an exact way of doing things I suppose.

[EDC5]

On the Berlingo, there's no direct feedback from the EGR, so I think the way the EGR is measured is via the MAF. More EGR means less air expected by the MAF, too much or too little air through the MAF will assume incorrect EGR. Not an exact way of doing things I suppose.

That makes sense, the EGR flow can be calculated from the MAF reading less the displacement x rpm figure I suppose.

hopefully a new solenoid valve will sort it for you.

[cancunia]

Yep, I'm hoping the replacement solenoid will put things back to normal. I'll report back when I have more info next week.

[cancunia]

Solenoid arrived & fitted. At first all seemed ok, but the engine went into limp mode again after a couple of stop/starts. While in limp mode, I got stuck in a traffic queue for about 5 mins, I left the engine idling. The fault somehow cleared itself while idling and has been fine for a couple of days, time will tell. I'm wondering if some kind of learning activity took place? On a similar note, has anyone use the Lexia 'replacement parts' option, particularly the replacement EGR?