Engine code P0401
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oilhammer
Certified Volkswagen Nut & Vendor
Insufficient EGR flow.
PounDDer
Veteran Member
I had the same problem on a cavalier once. It was a bad fuel cap. You can try that first.
NarfBLAST
Top Post Dawg
Clear it and see if it comes back.
It may be that your MAF is reading too low.
Try my MAF xGauge and see if your MAF is reading correctly at idle and at 3000RPM using your scangauge see link below. If you are not sure post the numbers from the xGauge MAF at idle and when accelerating...
Has the car had the EGR adapation using VAG-COM? Do you know if your EGR valve is working, or if it has been blocked off?
It may be that your MAF is reading too low.
Try my MAF xGauge and see if your MAF is reading correctly at idle and at 3000RPM using your scangauge see link below. If you are not sure post the numbers from the xGauge MAF at idle and when accelerating...
Has the car had the EGR adapation using VAG-COM? Do you know if your EGR valve is working, or if it has been blocked off?
2004STARWARSTDI
Top Post Dawg
- Joined
- Oct 19, 2004
- Location
- LAKELAND, FL
- TDI
- 2004 Platinum Gray GLS Jetta / 2006 Silver Jetta with DSG
NarfBLAST
Top Post Dawg
Those are the VAG codes, but if you only have an OBDII scanner that will not help unfortunately...2004STARWARSTDI said:
I can't find a list of codes right now but I tend to just search on P0401 in google and you get an answer pretty quick, but P0401 on the ALH TDI is actually counterintuitive:
On the ALH TDI P0401 mean EGR Insufficient flow. This does not mean that there is insufficient flow thru the EGR valve! It actually means that the "EGR system has detected insufficient flow at the only sensor it has to measure flow which is the MAF sensor." Flow may be low at the MAF sensor for two reasons: 1) EGR valve may be stuck open filling the intake with exhaust gas and causing LESS fresh air to go past the MAF sensor. 2) the MAF sensor is reading lower than expected.
pete3221
Veteran Member
I just got this code on my '03 Bora. What would ya do try to clean up the MAF sensor?
The engine management system on these TDI's are much more basic than the gas cars. For the most part unchanged from 1996 through 2003 as far as EMS.PounDDer said:
They have no problems with gas cap as this is not monitored. I have the pleasure to have to fix all VW models with all engines. How I wish the that the gas cars were simple as the diesel. If you believe me check the list if fauilts codes that are possible for the gas and compare it to the diesel.
brucep
Veteran Member
The reason P0401 is not trivial to understand in this case is because it is trying to tell you negitive logic.
First and foremost one must understand that more flow thru the EGR system means LESS flow thru the MAF.
Since there is no sensor for "flow" on the EGR system, the onbaord computer trys to use inverse-logic to calculate how much gas is flowing thru the EGR system by making the assumption that the MAF will measure LESS flow when the EGR valve is open.
Coantrary to what an above appender says... this DOES MEAN that the flow thru the EGR (as calculated) is lower than expected. We also know this means that the flow thru the MAF is MORE than expected when the EGR valve is open.
Personally, since there are other diagnostics which are run to acertain the accuracy of the MAF (and they are not flagging any problems) ... I would start by assuming that the MAF is *NOT* the problem and look for somthing plugging the EGR system.
I hope this description helps you understand what is being measured and why it is not straignt-forward to understand what is going on here.
First and foremost one must understand that more flow thru the EGR system means LESS flow thru the MAF.
Since there is no sensor for "flow" on the EGR system, the onbaord computer trys to use inverse-logic to calculate how much gas is flowing thru the EGR system by making the assumption that the MAF will measure LESS flow when the EGR valve is open.
Coantrary to what an above appender says... this DOES MEAN that the flow thru the EGR (as calculated) is lower than expected. We also know this means that the flow thru the MAF is MORE than expected when the EGR valve is open.
Personally, since there are other diagnostics which are run to acertain the accuracy of the MAF (and they are not flagging any problems) ... I would start by assuming that the MAF is *NOT* the problem and look for somthing plugging the EGR system.
I hope this description helps you understand what is being measured and why it is not straignt-forward to understand what is going on here.
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brucep
Veteran Member
Not P0442
No No No
... you are thinking of P0442 which is caused when the Evaperative Emmissions (EVAP) test fails on a gasoline-powerd vehicle. The EVAP test uses an air pump to build-up a small pressure in the airspace above the gasoline in the tank. Then, it is sealed off and a timer-sequence is initiated to determine how long this pressure is maintained.
A P0442 is flagged when the pressure cannot be built up at all. (A loose gascap is the most common cause of P0442)
A P0455 is flagged if the second part of the test fails (cannot maintiain the pressure.)
In fact, there are an array of P044x codes which are all related to the EVAP system.
Fixing cars is a peice of cake when one understands and KNOWS how the systems work.
Why do gasoline vehicles have an EVAP system?
1) To reduce gasolene fumes from getting into the atmosphere
2) To prevent EXPLOSIONS in underground parking decks. (Imagane if all the cars in an underground parking deck were leaking gasoline fumes into the air.... any spark would cause an explosion)
BTW: I do not beleive that TDI even *HAS* an EVAP system... so all of the above is just for folks who wish to have their knowledge enrichend.
PounDDer said:
No No No
... you are thinking of P0442 which is caused when the Evaperative Emmissions (EVAP) test fails on a gasoline-powerd vehicle. The EVAP test uses an air pump to build-up a small pressure in the airspace above the gasoline in the tank. Then, it is sealed off and a timer-sequence is initiated to determine how long this pressure is maintained.A P0442 is flagged when the pressure cannot be built up at all. (A loose gascap is the most common cause of P0442)
A P0455 is flagged if the second part of the test fails (cannot maintiain the pressure.)
In fact, there are an array of P044x codes which are all related to the EVAP system.
Fixing cars is a peice of cake when one understands and KNOWS how the systems work.
Why do gasoline vehicles have an EVAP system?
1) To reduce gasolene fumes from getting into the atmosphere
2) To prevent EXPLOSIONS in underground parking decks. (Imagane if all the cars in an underground parking deck were leaking gasoline fumes into the air.... any spark would cause an explosion)
BTW: I do not beleive that TDI even *HAS* an EVAP system... so all of the above is just for folks who wish to have their knowledge enrichend.
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PDJetta
Top Post Dawg
- Joined
- Nov 6, 2003
- Location
- Northern Virginia
- TDI
- '04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
" I would start by assuming that the MAF is *NOT* the problem and look for somthing plugging the EGR system."
The intake manifold AND the EGR cooler tubes both can clog quite nicely. I would start here.
And the EGR valve diaphragm can tear (this happened on my mother's '00 Jetta TDI, causing a CEL). Torn or disconnected vacuum line to the EGR valve can cause low/no EGR flow as well, as can lack of vacuum.
--Nate
The intake manifold AND the EGR cooler tubes both can clog quite nicely. I would start here.
And the EGR valve diaphragm can tear (this happened on my mother's '00 Jetta TDI, causing a CEL). Torn or disconnected vacuum line to the EGR valve can cause low/no EGR flow as well, as can lack of vacuum.
--Nate
fixumrich
The Periodontist
Vacuum line from egr to valve shot .. Or diaphram in erg valve weak or blown.. There is a vac test for the egr diaphram.. Good luck Rich !
jjpsuperdad
Well-known member
P0401 code fault we found this with our tdiOur 2003 TDI jetta had the EGR cooler clogged and WE mean Clogged ! it is so bad we can't even clean it with out damaging it which is what happen.
SO IF YOU HAVE P0401 IT VERY WELL COULD BE A CLOGGED EGR COOLER!!!
lodraghispeed
New member
P0401
This code has repeatedly appeared, along with a check engine light, since I've owned this vehicle. Now, after the recent scandal, it majically appeared again. Took it into the dealership, and can you believe, these crooks are trying to dance their way out of it and forcing me to pay for a job that was botched from day one.
No wonder they're gonna get sued. Their service centers probably recruit from prisons.
This code has repeatedly appeared, along with a check engine light, since I've owned this vehicle. Now, after the recent scandal, it majically appeared again. Took it into the dealership, and can you believe, these crooks are trying to dance their way out of it and forcing me to pay for a job that was botched from day one.
No wonder they're gonna get sued. Their service centers probably recruit from prisons.