Golf Mk5 Intermittent Dead Throttle & Sensor Reference Voltage A

   #1  

Jim Beagley

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I have been looking into a frustrating intermittent fault on a 2006 Mk5 2.0 Tdi 4 Motion with the BKD engine. A full Autoscan is attached below;

Initially, this was a very intermittent fault. The car would drive fine for days, then occasionally the throttle pedal would go dead. Backing off the throttle pedal fully and then pressing it again would clear the problem. This did not cause the car to throw any fault codes.

After a while, the problem worsened with the car becoming difficult to drive and finally throwing the following fault codes;

17026 - Sensor Reference Voltage A
P0642 - 000 - Voltage too Low - Intermittent
16725 - Camshaft Position Sensor (G40)
P0341 - 000 - Implausible Signal - Intermittent
16611 - Throttle Pedal Position Sensor (G79)
P0227 - 000 - Signal too Low - Intermittent

I replaced the camshaft sensor and all seemed fine for a couple of weeks until the problem returned. Looking at measuring blocks, the throttle position sensors are both reading correctly and without glitches when plotted on a graph even when the fault is occurring. The cam and crank sensors also read correctly when the fault is occurring. I disconnected the brake pedal switch to check it was not shorting, as I know the engine will not rev with the brake pedal depressed – no luck there. I have tried disconnecting the other sensors one at a time to see if the fault clears but no luck so far.

I have checked all fuses and cleaned and checked all the fusible links on the fuse box in the engine bay. I have also removed and checked the ECU plugs in the bulkhead, and inspected the wiring looms.

Does any kind person please have a list of which sensors and senders are fed by Reference Voltage A, or a wiring diagram for this car? I am still thinking that one of the sensors is shorting internally causing the ref voltage to drop?

Some other observations - when the fault occurs, the cruise control stops working, and the green light on the dash goes out (I know this as I have tried to use the cruise control as a ‘get you home’ measure when the throttle becomes unresponsive). The fault does not seem to be related to warm/ cold/ wet/ dry but is completely random. It appears to be completely fine some days. At other times the car is pretty much undriveable. The fault code that recurs most often is the general reference voltage fault. I assume the other codes are caused by the drop in the reference voltage?

I feel like I’m looking for a needle in a haystack and I’m hoping someone might be able to give me a few pointers and reduce the size of the haystack!

Many thanks! Jim

Code:
Monday,23,November,2020,17:55:32:06582
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 20.4.2.0 (x64)  HEX-NET CB: 0.4513.4
Data version: 20200730 DS317.0
www.Ross-Tech.com


VIN: WVWZZZ1KZ6W130068   License Plate: NJ06PXR



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                Address 01: Engine       Labels: 03G-906-016-BKD.clb
Control Module Part Number: 03G 906 016 AQ    HW: 028 101 184 8
  Component and/or Version: R4 2,0L EDC G000SG  9971
           Software Coding: 0000172
            Work Shop Code: WSC 66565 257 00032
                      VCID: 72A827C26DB6971615-8026
3 Faults Found:

16725 - Camshaft Position Sensor (G40)
            P0341 - 000 - Implausible Signal - Intermittent
             Freeze Frame:
                    RPM: 819 /min
                    Torque: 26.0 Nm
                    Speed: 0.0 km/h
                    Load: 27.5 %
                    Voltage: 14.06 V
                    Bin. Bits: 00001100
                    Idle Stabilization: 0.0°KW
                    (no units): 48.0

17026 - Sensor Reference Voltage A
            P0642 - 000 - Voltage too Low - Intermittent
             Freeze Frame:
                    RPM: 819 /min
                    Torque: 24.0 Nm
                    Speed: 18.0 km/h
                    Bin. Bits: 00100000
                    Bin. Bits: 00100000
                    Bin. Bits: 00100000
                    Bin. Bits: 00100000
                    Bin. Bits: 00100000

16611 - Throttle Pedal Position Sensor (G79)
            P0227 - 000 - Signal too Low - Intermittent
             Freeze Frame:
                    RPM: 1029 /min
                    Torque: 0.0 Nm
                    Speed: 53.0 km/h
                    Load: 0.0 %
                    Voltage: 14.44 V
                    Bin. Bits: 00001111
                    Torque: 156.0 Nm
                    Bin. Bits:  0 01  0


Readiness: 0 1 0 0 0

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Address 01: DTCs cleared
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Address 01: DTCs cleared
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Address 01: DTCs cleared
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Address 01: DTCs cleared
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Address 01: DTCs cleared
 
   #2  

Bruce

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Wiring Diagrams are available for a small fee here: Official Factory Repair Information

Ref A should be generated by the ECU and goes to several sensors. The wiring diagram would be the place to start to find all the sensors that use Ref A. Then I would think you should start chasing the wire from the ECU pin to the sensors. As you have said it is intermittent, I would be thinking connection issues.
 
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Jim Beagley

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Thank you for the assistance. I have an erWin account, and printed off the wiring diagrams. Unplugging all the sensors on the circuit does not seem to make a difference.
Since the last post, I have been through all the earth points, load checked all the wiring from the ECU pins to the sensors, and swapped out various items with known good parts from another car, including throttle position sensor, and crank/ cam/ map sensors. I have also checked the reference voltage at the ECU, and it seems to be a constant 4.98V.
The fault is still completely random. I drove a quite a few jubilant miles this evening without any hint of trouble, confident it was fixed, then it happened again, and I limped home with my tail between my legs.
Curiously, sitting in the car with the engine running at idle, the fault will randomly come and go seemingly without any pattern or stimulus - very strange...
I have reference voltage module in my tool box that supplies a constant and precise 5V for testing sensors. Do you think it would do any harm to plug it in to the ‘reference voltage A’ circuit at one of the sensors and back-feed the circuit to see if that eliminates the fault?
 
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Uwe

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I have reference voltage module in my tool box that supplies a constant and precise 5V for testing sensors. Do you think it would do any harm to plug it in to the ‘reference voltage A’ circuit at one of the sensors and back-feed the circuit to see if that eliminates the fault?
As long as it's not fighting with the output from the ECU (i.e. don't parallel the two supplies), I don't think there's any harm in it.

-Uwe-
 
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