vw sharan tdi low power ahu engine

[landroverbob]

AUDI1Z

--*Apologies entirely unnecessary, help is appreciated. Just to explain some circumstances , I am non french technical speaking living in rural france, the garage is 20k from my farm and are helpful but always very busy, the car belongs to a one parent family with little budget to spend and garages are known to take advantage or just keep fitting parts until it's mended. - All my own vehicles/toys are deliberately non electronic*
What you observe is symptomatically for an engine going into limb mode because of a temporary error observed by the ECU, lasting for some seconds and classified dangerous for the engine. *I understand that but - when at the garage last week we cleared the ecu memory the fault reappeared immediately the engine was run again, before driving it on the road. I then drove it on the road for a few k's till going up it's favourite hill the power dropped as per usual*
Once you stop and re-ignite, or even let go the gas pedal and then throttle up again, the limb mode is left, and the engine comes up again.--*Only switching off then back on resets it from limp, throttle change doesn't*
Typical fault conditions are a too high manifold pressure (overshoot),--*maximum was around 1bar /15psi on my temporary tee'd in boost gauge*
or a misrelation between manifold pressure and intake air mass.-- * I intend doing the air mass next on the garage auto- diag and will try to get them to let me do manifold pressures too*
The latter would happen if e.g. the ECU internal hose to the pressure sensor would have a leak, *I tried vacuum testing initially and since then a pressure test and it holds 18psi without dropping, when I replaced part of the worn hose that goes to the ecu I also cut it open and found it free of oil inside*
but other reasons are credible, too. I personally had this situation with defective intake hoses, but also with oil in the hose going from the intercooler to the pressure sensor in the ECU. When you reach a certain load condition, engine power is suddenly gone.
For the case you can not find a broken intake hose, or another evident mechanical defect, the search becomes more difficult.
Without having measurement equipment, you can perform a driving test with the N75 regulator valve electrically disconnected. --* I have not done that as I had the boost gauge fitted and it still produced the same boost after the power dropped -but I will do that tomorrow anyway*
When the fault disappears, either the valve or its supply is defective (I have read that you measured the valve resistance), nevertheless do the test.
For further checks, you need to read out the ECU during defined driving conditions, particularly the requested/real values for the intake manifold pressure, * thats one thing I will have difficulty doiung but will be trying*and the control level of the N75 pressure boost valve.
Manufacturers values for turbocharger check are:
Full throttle acceleration from 1500min-1 to 3000min-1. Manifold pressure to be reached at 3000min-1 is 1550 mbar to 1750 mbar w/o N75 operating, 1800mbar to 2050 mbar w/ N75 operating. --* it never exceeds 1bar/15psi under full throttle load which is the pressure I have used to mechanically test the actuator fully opens the wastegate - are you sure of those figures, isn't 2050mb around 30psi?*
Note that this test must not detect all faults when done with an external pressure gauge, it is important what the ECU reads.
Error 65535 is imho no indication for a failure in the intake pressure tubing. The ECU can not distinguish between a leak inside, and a leak outside, in the sensor tube or in the intake hoses. All is connected together.

Hope you can understand my replies LRB.

[landroverbob]

Thanks Chitty, ecu is behind the dash and a real pig to get to so I have had pressure tested it through it's own hose fom the manifold end and it maintains 18 psi. Also when replacing part of ther original hose I cut open the piece I removed and found it dry of oil inside. The inlet pipe from the intercooler to the manifold which the map sensor hose is fitted into is rather oily inside however. Answered Audi1z with a long reply, asked him if his boost test figures were correct, sounds a lot of boost or am I misunderstanding?

[audi1z]

Hi,
The communicated test pressure figures are absolute pressure (manufacturer original), not pressure relative to 1 bar/ambient.
Because the error message you refer to seems to originate from a potentially bad communication with a third party measurement device, you should consider to visit a Volkswagen Service and to ask there for readout of the ECU error codes. The alternative would be to purchase (or at least loan) an original VCDS from Ross-Tech, with correct set-up of the interface.
Regards

[landroverbob]

Once again thanks Audi1z and Chitty
Disconnected the n75 and road tested and the power drop/limp occured on cue. I took the bosch maf sensor out to get the numbers in case I needed them and as expected it looked ok.
I was able to use the scanner at the garage late afternoon and drove the car with it plugged in, the actual boost pressures agreed approximately with the desired pressures and were within the parameters you gave (I understand why they seemed high to me now you have explained) but unfortunately the scanner battery failed before I reached the hill where problems occur and before I could try the maf comparisons and when I returned to the garage it was closing time so I could not carry on.
I am hoping to rely on their good nature to let me try again and I'll post the results
I can't remember if I have said but disconnecting the maf sensor when the car is running correctly produces the same power drop and driving feel but I guess it has gone into limp mode then so bound to be the same.

I quite accept that the scanner may be correct and there is an ecu problem and will need to be replaced but have read several posts where that's been done on the basis of fault codes and not fixed the problem. It's not my money I'm spending so I want to be as sure possible before doing
that and of course for me is understanding how it all works plus making information available to others with problem cars.

[landroverbob]

Was able to use scanner yesterday, cleared all faults. Couldn't have the scanner again for an hour so the car was parked up. I then drove it with the scanner connected and set to view "desired air flow" and "actual air flow." Comparison pretty close under all throttle conditions, slight lag under fierce aceleration but after about 20kms gradually getting a bigger difference between readings on sharp pedal depression. On the problem hill in the by now usual place in 4th gear, full throttle around 4000rpm it went into limp mode. Traffic caused me stop and when stationary at tickover both readings were the same, revving the engine to 4000rpm the "desired" read 830 when the "actual" read 590. I repeated this several times with similar results then went into fault reading and for the first time ever got intermittent air mass metering fault as well as the usual permanent ecu fault. Would anyone think it can be the ecu. It's a bosch meter 0280 217 121 copies are cheap on ebay and feedback shows they work even if perhaps not for long? but I will ask around first and see if I can borrow a working unit to tryfirst

[chittychittybangbang]

There's always a possibility of a problem with the ECU, maybe the sensor inside the ECU is bad instead of the vacuum line. but that error code is normally a bad vacuum line somewhere along the sensor's route. The meter going to only 590 actual when 830 is requested indicates a problem. However, since it's new, try fixing the first problem first. The meter not going to max could be clogged exhaust, bad EGR, bad EGR control (the EGR displaces the intake air), and of course, bad air flow meter.

[Seatman]

Don't forget the waste gate can stick, that's what happened on my Cordoba. I would just make sure the actuator rod moves freely just in case. As for the ecu on your sharan being awkward, I think most things on them are a touch awkward. My friend has one and doing the timing belt and brakes was a bit of a challenge especially getting brake fluid into the resivior. Also what about the possibility of the actuator having a damaged diaphram? I would check it despite what the boost gauge reads just to be certain.

[audi1z]

Hi,
0280 217 121 is not the complete part number. There is surely a letter belonging to the P/N, and this is important.
Regarding the error code 65535, again, the ECU can not distinguish between a leak in the sensor hose and the intake. It a leakage case, it will display something like 00575-xxx, but not 65535. 65535 is originally a defect ECU (computer), but also indicates a communication problem.
The observation indicates that the engine gets under high load too less air. One cause may be a defect in the exhaust gas recirculation. Does it close?
Regards

[ixeras]

Hey!
I have the same problem with my sharan AUY.
Came error codes: air mass meter incorrect- I have changed
turbo regulating problem
I found diaphragm in EGR was broken- EGR valve was changed.
Now the car does not miss the power, but it sneezes with releasing gas pedal after high rpms just like before.
Sorry about my english.
Edvard

[JoesAuto]

.... I live in the mountains in Eastern Oregon, not exactly sure if your model is similar. We have several TDIs running around here, on several occassions we have had the intake completely plug up with carbon. I have seen these occompanied with intake codes. They are easy to inspect and fairly easy to clean out. Definately a lack of power and for whatever reason better and worse at times, but even with full boost it just cant get past the carbon. Again not sure if it is applicable here but the complaint sure sounded familiar!!!
Good luck!!!