2.0 TDi EGR flow

[Shahzaib]

Hi,

I would really appreciate some advise on a fault that keeps reappearing and having read other posts on this I think a lot of other people need this information as well.

16785 - EGR System: Insufficient Flow
P0401 - 000 - - - Intermittent

I have searched the forum and found quite a few people discussing this but no real solution other than to remove the egr at software level.

So the engine I have is a 2.0TDi BKD. Over the period of a year I have cleaned out the inlet manifold, replaced the motor intake flap and the egr valve. I have also recently cleaned out the changer over flap on the egr cooler which was not moving very well. All seals, gaskets, vacuum pipes and diaphragms seems to be in good condition and doing their job.

As well the fault code above I have noticed that measuring block 3 shows actual egr flow and expected egr flow to be out by roughly 100 but only at idle and low rpm.

Now my guess it that the ecu is getting incorrect readings from one or more of the sensors involved, this is the part I need help with. I would like to know which sensors are involved and where they are located.

Thanks for any help and I will keep updating with any new findings.

[martin1810]

The EGR flow is calculated from the MAF flow rate as measured by the AMM (MAF). It is double checked by the lambda sensor if you have one. This is usually only present on engines with DPF. You need to run a VCDS engine measuring block scan during a 10 min warm engine drive. That way you can examine what the MAF thinks is happening.

[Shahzaib]

Hi Martin,

Thanks for the speedy reply.

I did run a log but the engine was not fully warm and I do not have a DPF so that’s one thing eliminated

I have attached the log anyway and will do another one later on today.

What should be expecting to see and how should I drive during the log for best results.

Regards

[a8 tech]

Hi,

I would really appreciate some advise on a fault that keeps reappearing and having read other posts on this I think a lot of other people need this information as well.

16785 - EGR System: Insufficient Flow
P0401 - 000 - - - Intermittent

I have searched the forum and found quite a few people discussing this but no real solution other than to remove the egr at software level.

So the engine I have is a 2.0TDi BKD. Over the period of a year I have cleaned out the inlet manifold, replaced the motor intake flap and the egr valve. I have also recently cleaned out the changer over flap on the egr cooler which was not moving very well. All seals, gaskets, vacuum pipes and diaphragms seems to be in good condition and doing their job.

As well the fault code above I have noticed that measuring block 3 shows actual egr flow and expected egr flow to be out by roughly 100 but only at idle and low rpm.

Now my guess it that the ecu is getting incorrect readings from one or more of the sensors involved, this is the part I need help with. I would like to know which sensors are involved and where they are located.

Thanks for any help and I will keep updating with any new findings.
if you check egr flow at idle be sure to rev the engine as egr will shut off and this fault is normally down to the egr valve chest located on the bulkhead and you can simply final control test this if the maf is defective the egr shuts down
when final control is active check the egr % against duty cycle but as I have mentioned the most common cause is the egr solenoid within the valve chest.I can not open your log file and this diagnosis is based on experience with your fault code unless you have some restriction in the egr or collapsed vacuum pipe(depleted vacuum insufficient opening of the egr plunger) restricting the flow rate, also consider signal voltage for interference/resistive circuit

[martin1810]

If you graph your log using timescale as bottom axis you will see that EGR actual peaks above spec when the engine starts to rev up. This is your intermittant fault. I would normally say the egr valve is sticking but you have replaced that. Best guess, the cooler flap is sticking and restricting flow to the egr valve. The shape of the graph suggests a sticking valve/flap rather than a restriction iin a pipe. A vacuum leak could cause a similar fault but a faulty valve or flap is more likely.

[a8 tech]

Martins comments are valid but consider n18 in the vacuum chest on the bulkhead as mentioned prior is a pretty good starting point and due to the number I have replaced odds on bet

egr cooler is unlikely but simply mti vac test it when testing egr at IDLE or with output test as this is the best method for checking operation remembering the vacuum will deplete as the test runs

[Shahzaib]

Hi,
Thank you all so much. although I've been busy decorating and unable to reply I have been reading and do plan to fiddle tomorrow.

A8, am I correct to assume the n18 you refer to is the black square box attached nearer to the windscreen end of the engine bay and has a number of pipes leading out of it? I'm a little confused as I'm sure I've read somewhere that N18 is the EGR valve.

I've tested the coolers change over flap for movement and its ability to hold vacuum and the same with the egr valve both seem to work fine.

I will give all your suggestions a try tomorrow and do some more logs.

Thank you for all your help, this engine management light is really annoying me now, hopefully I can get to the bottom of this tomorrow.

[a8 tech]

Hi,
Thank you all so much. although I've been busy decorating and unable to reply I have been reading and do plan to fiddle tomorrow.

A8, am I correct to assume the n18 you refer to is the black square box attached nearer to the windscreen end of the engine bay and has a number of pipes leading out of it? I'm a little confused as I'm sure I've read somewhere that N18 is the EGR valve.

I've tested the coolers change over flap for movement and its ability to hold vacuum and the same with the egr valve both seem to work fine.

I will give all your suggestions a try tomorrow and do some more logs.

Thank you for all your help, this engine management light is really annoying me now, hopefully I can get to the bottom of this tomorrow.

Yes the black box is the one
When testing in basic setting or output test the rpm will increase from idle then test on test off
You can check and compare the values this is easier with vas as it gives you more data than vcds


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[Shahzaib]

A8, I did the output test and watched/felt for movement in the egr cooler flap and all seems to be work well there. I also think the egr cooler may be leaking as i do loose a little coolant over time. Could this possibly be the cause of my troubles?

[a8 tech]

to test for coolant loss

run the engine to normal temp

allow to cool and then apply a coolant pressure test at 1 bar for 48 hours and note if the coolant drops in the header tank

If it drops and you start up the engine and there is a misfire then its likely the head is cracked
You can confirm this by removing the cooler and inspecting and remove the inlet manifold and check for coolant in the ports of the head

neither the cooler or the head will cause your fault and its more than likely a leaking valve block dropping vacuum as mentioned before or within the block sticking egr solenoid n18

get one from a breakers if unsure so your not shelling out to much ad the fault is normally intermittent so harder to trace because when you test the system it always works

i spent 4 weeks sorting one out when 8p platform first came out and replaced everything and since i have done a good few and its always been n18, i had loads of road test logs and you could see the value of the duty cycle stick briefly when it occurred and I had a make shift vacuum gauge inside the car

like i said i driven round for 4 weeks like this lol

good luck

[Shahzaib]

A8 I've taken your advice and changed the solenoid block for one from a breakers yard and although the light hasn't returned yet the spec and actual egr flow are still quite different. What do you suggest I try next?

[a8 tech]

just run it, dont forget egr will alter as there is no exact map for it it reacts to ecu duty cycle from inputs like coolant temp air mass etc

[Shahzaib]

The light has returned with the same fault.

There was another thing I did which was a basic setting on channel 3 as described here (http://www.audi-portal.com/en/diagnostic/ecu_10565.html#1), this didn't make any obvious difference.

I think the next thing I'll be doing is removing the egr cooler and inspecting the change over flap internally, when I first moved it by hand it was quite stiff and I was able to free it up by forcing it to move.

[a8 tech]

take all the egr pipes off and clean them also make sure no one has fitted the reduced diameter gaskets

[Shahzaib]

A8. Just thought I would let you know that you were correct with the EGR solenoid. Light went out a day after and has been off since with no fault codes, although the actual and spec egr flow are closer now the actual is still out by about 30. Is this normal or is there possibly still something not quite working 100%?

Also the only egr solenoid I could get my hands on from a breaker was from a passat. Same part number but slightly different mounting. I improvised just to test things out. I've ordered a new one should get it Friday or Monday.

Thank you for all your help.


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[a8 tech]

good news, egr actual and specified can vary but don't be to concerned unless a fault reoccurs

[ronnyy]

to test for coolant loss

run the engine to normal temp

allow to cool and then apply a coolant pressure test at 1 bar for 48 hours and note if the coolant drops in the header tank

If it drops and you start up the engine and there is a misfire then its likely the head is cracked
You can confirm this by removing the cooler and inspecting and remove the inlet manifold and check for coolant in the ports of the head

neither the cooler or the head will cause your fault and its more than likely a leaking valve block dropping vacuum as mentioned before or within the block sticking egr solenoid n18

get one from a breakers if unsure so your not shelling out to much ad the fault is normally intermittent so harder to trace because when you test the system it always works

i spent 4 weeks sorting one out when 8p platform first came out and replaced everything and since i have done a good few and its always been n18, i had loads of road test logs and you could see the value of the duty cycle stick briefly when it occurred and I had a make shift vacuum gauge inside the car

like i said i driven round for 4 weeks like this lol

good luck

I have a Golf 6 from 2009. Could I replace the n18 by myself? I'm less experienced then you are but willing to learn fast. Is it complicated to replace just the n18 on a MK6?


Many thanks