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Discussion Starter #1
Hi

I am new to the forum but have a confusing problem I hope someone can help me solve. My car has the ALH 90 bhp 1.9 TDI engine as in the mk4 Golf and several other cars, with an automatic gearbox.

I am trying to decide how to approach solving my limp mode problem as described in this original thread on another forum:

http://briskoda.net/diagnostics-vag-com/help-diagnose-limp-mode-1-9-tdi/158689/#post1849278

I have established a pattern where limp mode is accompanied by this dtc when asking for sustained high power overtaking on an uphill stretch of motorway:

17965/P1557/005463 - Charge Pressure Control: Positive Deviation

but is accompanied by this dtc when I hit the pedal hard and fast with the autobox (which is a bit clunky compared with some others I have driven) on a steep hill:

17563/P1155/004437 - Manifold Abs.Pressure Sensor (G71): Circ. Short to B+

I think I have a sticky vanes/actuator rod problem necessitating a reconditioned turbo, but the apparent electric fault is confusing. When checked by the local independent specialist on VAG cars he confirmed that the ECU was reading overboosting from the MAP even though on that occasion no clear cause (N75 valve, vacuum lines and actuator rod movement all checked out fine at the time) could be established and the car did not go into limp mode on a road test. I do however understand that the sticky vanes problem is very irregular and intermittent.

Trying to understand the German on the link from the ross-tech wiki page for the 17563 fault I can see that the G71 sensor is designed to send signals to the ECU between just above 0 at 200 mbar and just below 5 volts at 2500 mbar (i.e. a maximum of 1500 mbar or about 21-22 psi boost over atmospheric pressure). I also see that the German site lists 2 codes not in the ross-tech wiki - 17564 which google translates as "interruption/short to ground" and 17565 which google translates as "supply".

This is where I need some help from an auto electrician. Does the ECU throw a 17563 error if it sees 5v coming down the signal wire because this is what it would see if there was a true "short to B+" and is this the same signal the ECU would see if the charge pressure exceeded the MAP sensor design maximum of 2500 mbar? I ask this because what VAG-COM measuring blocks I have been able to do by reving up the engine not under load (my VAG-COM is on a desktop with an extended cable through the sitting room window, rather than a laptop) do show high spikes of the actual MAP against requested MAP. I am wondering if the apparent electrical fault is a red herring and the system is indeed overboosting beyond the MAP sensor design limit when the autobox kickdown jerks the system against the sticky vanes problem. I am also guessing that the 17564 dtc for circuit break/short to ground is generated by the ECU when it detects no volts signal coming from the MAP??

I may be talking out of my proverbial a*s" as it is a long time since I did electronics at school, but would appreciate any comments from an electrician on this before I spend £500 having a reconditioned turbo fitted that may not solve the problem.

Thanks in advance.
 

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It sounds like you have done a lot of trouble shooting but have you confirmed that all wiring is good? Manifold sensor circ. short could be just that - a wire is rubbing through or bad sensor. That could cause the other code and limp mode. And if you suspect a bad sensor it's a lot faster and easier to change.
 

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Thanks for the reply.

I have assumed the sensor is not bad on the advice of my local VAG independent specialist who said that the sensor is sending the right signal at idle (i.e = atmospheric pressure) when he put VCDS on it, and goes up with increased revs/load - he said it would not do that if bad, but I would be happy to be put right by an auto electrician.

I have also more tentatively assumed the wiring is not bad as the error code is only ever generated by the act of flooring the pedal up a steep hill.

Like all intermittent faults, this one is proving very difficult to nail down. However, if I reach the point of being close to spending serious money I will probably replace the sensor and bypass the existing wiring to the ECU first as that would be less than £100 instead of £500.

Before anyone tells me I should remove the turbo, strip it down, clean it out and re-fit it myself, I know my limits!!
 

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I can't describe the function of the sensor but it isn't a common failure. Like the mechanic said, an ECU fault is 1/1000. But having said that, the VW mk4 ECU have had more fault than what I would consider normal. Normally an ECU fault is 1/10,000. It might be worth it to swap the ECU and see if it changes. If it's like a VW and you have an immobilizer you must have the SKC number to swap ECUs. See the immobilizer FAQ for more details.

Have you replaced all the vacuum lines? Often there's a small leak or crack that doesn't show up until it's under stress. This would cause an intermittent problem.

You could also have a boost leak. Look through the FAQ for boost leak check or test. I don't believe it would cause the 2nd code you have but it's worth a try.
 

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I don't think limp mode will cause a sensor short. It's probably rubbing through somewhere or check all the grounds. Maybe a ground wire is broken? Are you sure the N75 boost solenoid is working?
 

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Discussion Starter #6
Fault Codes 17965 and 17563

Thought I would just post the final resolution of this.

Tried a turbo cleaning kit from Innotec applied by local garage up the turbo's a*se - £90 in the money pit - both codes still there, still limp mode, still overboost showing in vag-com measured blocks.

Tried MAP sensor replacement and all new wiring from sensor to ecu - £130 in money pit - as above.

Tried replace all vacuum/air pipes and swap EGR with N75 (even though all had seemed OK on inspection) - £40 in money pit - as above.

Tried exchange reconditioned turbo (nasty job for the fitter as no room to work with autobox gubbins in the way) - £600 but success - no limp modes, both codes gone, no overboost measured in vag-com.

So for anyone who gets these 2 codes together, don't assume that the 17563 "map sensor short to positive" code is necessarily an electrical problem.
 
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