Question about 2000 Volkswagen Jetta TDI
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Posted on Jan 02, 2017
SOURCE: Insufficient EGR Flow problem
Specifically DTC P0401 is "Exhaust Gas Recirculation (EGR) Insufficient Flow". Now this is where we have to be careful when we read a code. In this case it is not saying the EGR valve is bad, it's saying the EGR flow is too low. Now it could be because the EGR valve is bad. Or it could be a clogged EGR tube or a broken vacuum line. This is why you have to be careful and check the whole system before you go changing parts.
The PCM tests the EGR system during deceleration by momentarily commanding the EGR valve to open while monitoring the Manifold Absolute Pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set DTC P0401. The number of test samples required to accomplish this may vary according to the amount of detected flow error.
Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.
To check the system first you need to remove the EGR valve and if it is clogged or broken. If it is, clean or replace it. If it is okay, then remove the EGR inlet tube from the exhaust manifold and the EGR outlet tube from the intake manifold. If either or both are clogged, clean them out or replace them. Then check the ports in the manifolds themselves to see if they are clogged. If so, clean them out.
When you are done, disconnect the battery for about 30 seconds to clear the code and drive the car to see if the light comes back.
This should take care of the problem. If not, then you will need to put a scan tool on the car and see what the EGR control system is doing wrong and correct it.
The Valve on this car is electronic, so, unfortunately a vacuum pump will not work for testing.
If you have a scan tool, you can command the pcm to open the valve to see if the valve itself is working.There are really only4 things to go wrong with these things, PCM, wiring,the valve itself, or plugged passages. I have never seen the pcm cause this problem, or the wiring for that matter. If you say you have pulled the EGR and checked the intake passages, then I would be pretty confident in saying the the egr valve itself is bad.
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Posted on Mar 18, 2009
vacuum leaks on intake manifold,
the air tube between the air filter.
intake manifold vacuum hose.
clean throttle plate with Berryman carburator cleaner
SEE sample picture HERE
Also remove carbon built up behind the EGR valve and the EGR passage tube.
Vacuum leak WILL offset the intended 14.7 to 1 air fuel ratio.
More un-metered air (leaks) will lean out the fuel mixture.
Use small amount of Berryman carb clearer at potential air leak area will help you identify trouble spot.
At idle,just spray and listen for the RPM surge.
The in-rush of carb clearer will increase the RPM on the motor.
Record the problem spot(s) and address it later.
EGR carbon built up require 2+ hours to clean from start to finish.
You will need a new EGR base gasket before your start.
Locate and remove the EGR valve after the vehicle is cool down.
Carefully record the connector and vacuum line (for older vehicle) location by drawing an easily to follow diagram.
Remove the EGR valve.
Inspect the location of the carbon built-up inside the valve and the EGR passage tube.
SOAK these areas with WD-40 spary.
You will need a small screwdriver,cloth hanger and lot of newspaper and time to get this cleaning done right.
RE-SOAK the carbon and let it sit for over-night will also help.
One the last round,pass a shop vacuum of the EGR valve and the passage pipe.
Install the new EGR gasket and connectors.
Allow the vehicle to warm up outdoor to burn up any remaining WD-40.
Take it for a test drive.
Please rate my answer if it's useful to you.
Posted on Dec 19, 2009
Hi, The EGR valve itself is on a set of flexible pipework - usually stainless steel - which runs between the inlet manifold and the exhaust manifold. The EGR actuator valve is pneumatically / vacuum operated by a solenoid valve, controlled by the ECU ( aka the brane). It's not usual for the EGR valve itself to fail, more likely the solenoid valve or its electrical connector getting dirty. If you google for VAG TDI N75 valve you should get all the info you could possibly ever need :-)
Hope this helps, D.
Posted on Jul 16, 2008
find your local vw service center and see if they can plug their computer in to see if there are any codes on the cpu. there may be one for an intermitent for the turbo. i ran into the same problem last month and it was the turbo veins are sticky so occasionaly it lack power going up hills. it did not cause the check engine light to come on, but there was a code on the cpu when they checked it. if it happens again while you are driving, pull over, shut the car off for 10-30 secs then restart it and see if it makes a difference. when it happened to me i called my guy and thats what he had me do and it was like a new car after that.
Posted on Jul 24, 2008
SOURCE: power loss
Can't answer your last question but catalytic convertors that are just not working anymore won't cause any loss of power.
However, if they have shattered inside (they are kind of a ceramic honeycomb) they can dump junk into the exhaust system that can eventually clog your muffler or resonator.
Checking whether this has happened isn't difficult; after the warm up of the engine, either you or a helper needs to listen to the exhaust note. If firing of the cylinders is still distinct, the system isn't clogged with shrapnel; if it seems to hiss at higher RPMs, it is likely clogged.
This effect is easy to miss; I've had two failures and when cold, the engine would pull fine because the chunks of ceramic would fall to the bottom of the muffler and glue together somewhat. Once hot and agitated, they would clog the muffler and cause a severe loss of power but the idle would be OK. A hill that I would normally pull at 70 MPH, I couldn't top at all; had to sit and wait for things to cool down before proceeding.
It also seems some engines appreciate a bit of back-pressure in the exhaust system because the car gained in mileage and pulling power for several thousand miles before the clog became critical causing the mileage to fall sharply along with the power.
Posted on May 23, 2009
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