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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old May 14th, 2019, 17:06   #1
B-Line
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TDI(s): 2001 Jetta
Default Need help with p0402 code

I have a 2001 Jetta TDI with 440,000 miles and I知 having issues figuring out my p0402 code. When it first appeared, I thought this was simply a dirty EGR so I removed it and cleaned it as well as the intake. They were pretty dirty but far from clogged. I reset the code and it returned after the second start and full warmup. I checked all vacuum lines and everything looked good and tight. All vacuum lines were replaced about 1 1/2 years ago. I致e been looking at the mass air flow sensor and I知 not sure how to interpret the results from live data on my scanner. At idle the readings 14.3 g/s and at full throttle it is 101.83 g/s peak and settled to 89.45 g/s. I知 thinking these are too low but I知 not really sure. I feel the car is slightly down on power but nothing extreme. I did unplug the mass air flow sensor and lost some more power but nothing drastic. I知 not sure where to go next. Any help or advice would be greatly appreciated.
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Old May 14th, 2019, 17:12   #2
STDOUBT
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What about the wiring? The plug to the ASV.
Is your EGR leaking air or oil? When the valve bushing fails it will leak.
Seems you've done everything except rule out the electrical.
From ross-tech:
  • Check/Clean Exhaust Gas Recirculation (EGR) System
  • Check/Replace Exhaust Gas Recirculation (EGR) Valve
  • Check Wiring and/or Connector(s) from/to Exhaust Gas Recirculation (EGR) Valve
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Old May 14th, 2019, 17:31   #3
B-Line
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I did not check the electrical connections. What should I be looking for? I did pull vacuum on he EGR valve and it functions normally. I’m not sure how to check for air leaks. Thanks for your help
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Old May 14th, 2019, 19:43   #4
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OK, so if your EGR valve isn't spitting oily gunk onto your valve cover that's good. Undo the wire harness behind the AVS on the back of the EGR. Check for corrosion, check for chafed wires. Make sure the plug re-seats well.
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Old May 15th, 2019, 03:57   #5
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Not sure what wiring harness you are talking about, as there isn't one in that location on an ALH. The only wires back there are to the anti-shudder valve solenoid, and the breather heater, neither of which would cause this problem.

The EGR valve is a simple vacuum operated unit. Controlled by the vacuum regulator N18 valve on the firewall, the one closer to the center of the car.

EGR flow is monitored by the ECU watching the MAF value.

There is a Measuring Group you can watch the EGR operation, I forget which one but start at 001 and go up, it'll be in the first few.

Block 1 is RPM

Block 2 and 3 are actual vs. requested

Block 4 is EGR duty cycle

Check it at hot idle, actual and requested should match. After a few minutes of idle time, the EGR will shut off, and the actual will jump up (MAF), usually about 200-250. Rev the engine, let it return to idle, then it should go back to matching requested.

If it is NOT, you can check (while it is still commanding EGR), the vacuum to the line (the big one to the valve itself). There should be some there.

Then, using a vacuum pump (or a small length of tube and your lungs, it works) and see if you can operate the EGR valve directly. If not, if it will not hold vacuum, it is bad.

Keep in mind, the DTC "EGR excessive flow" actually means "MAF excessive flow" because the EGR is not working properly, no idea why VAG does that, but they do.

What I suspect is, your EGR is bad, vacuum is being bled off through the broken inner workings, causing low system vacuum in general, which is causing not quite ideal VNT control, which can cause a slight loss of power, especially at tip in.
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Old May 15th, 2019, 09:30   #6
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Thanks for the help. I did pull vacuum on the EGR and it opens and holds with vacuum applied.
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Old May 16th, 2019, 03:34   #7
tgray
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You may have a clogged EGR cooler with that many miles. A blocked cooler will give the same reading to the computer as disconnecting the EGR. Pull off the short tube that goes into the egr and start the engine. See how much exhaust blows out if any. Try gently pushing something like a copper electrical wire up the tubes to see if they are open.
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