2011 Caddy 1.6TDI wont start (vcds says Brake light Switch)

[AudisportUK]

Hi looking for some help with an annoying intermittant fault.

My 2011 Caddy 1.6TDI occasionally wont start, when I turn the key (whilst pressing clutch) I get a message on the display telling me to press the clutch to start. Eventually cycling the key on and off will make it go. I have scanned it in the past and VCDS says its the brake light switch at fault, so I replaced it but the problem remains. Once it happened and the brake lights were stuck on but I don't think this happens every time. I have noticed now that you can tell its going to happen as on the occasions it does, when you turn the ignition on the fuel pump does not prime.

I own VCDS and the last time it happened on Saturday I scanned it with the following result, fault in the ecu and in the central electrics, brake light switch in both and low voltage terminal 30 in ecu.

Any ideas? I know on earlier cars the clutch switch and brake lights are from the same power supply but on mine (according to the wiring diagram) they are separate supply but share an earth, could the clutch switch still be at fault or is this more likely a wiring or relay problem.

Thanks,
Phil



Address 01: Engine (J623-CAYD) Labels:. 03L-906-023-CAY.clb
Part No SW: 03L 906 023 DB HW: 03L 907 425 C
Component: 1,6l R4 CR td H43 8684
Revision: --H43--- Serial number: 00000000000000
Coding: 00114014030500080000
Shop #: WSC 35110 790 50316
ASAM Dataset: EV_ECM16TDI02103L906023DB 003004
ROD: EV_ECM16TDI02103L997557M.rod
VCID: 698FBE43A9FD2B9F7E9-803C
2 Faults Found:
6013 - Brake Switch (F)
P0571 00 [229] - Implausible Signal
MIL ON - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 112720 km
Date: 2019.10.13
Time: 09:55:42
Engine speed: 0.00 /min
Normed load value: 0.0 %
Vehicle speed: 0 km/h
Coolant temperature: 9 °C
Intake air temperature: 10 °C
Ambient air pressure: 980 mbar
Voltage terminal 30: 0.565 V
Unlearning counter according OBD: 40
Engine speed: 0 /min
Vehicle speed: 0 km/h
Accelerator position: normalized-Accelerator position: 0.00 %
Battery voltage: 0.6 V
Driver request torque-TQI_DRIV_SUB: 0.00 Nm
Number of resets of main unit-CTR_RST_MC: 0


6551 - System Voltage
P0562 00 [032] - Too Low
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 10
Mileage: 112720 km
Date: 2019.10.13
Time: 09:54:55
Engine speed: 0.00 /min
Normed load value: 0.0 %
Vehicle speed: 0 km/h
Coolant temperature: 9 °C
Intake air temperature: 10 °C
Ambient air pressure: 980 mbar
Voltage terminal 30: 0.113 V
Unlearning counter according OBD: 39
Sensor for engine block temperature: raw value-Coolant temperature: 9 °C
Engine torque-TQI_SP: 0.00 Nm
Accelerator position: normalized-Accelerator position: 0.00 %
selected gear-DRI: 0
Sensor for engine block temperature: raw value-Coolant temperature: 9 °C
Readiness: 0000 0000



Address 09: Cent. Elect. (J519) Labels:. 1K0-937-08x-09.clb
Part No SW: 2K5 937 086 B HW: 2K5 937 086 B
Component: BCM PQ35 M+ 011 1044
Revision: BD011001
Coding: 481A0A3A8025F16B088800829500816443217288524F816064 8000000040
Shop #: WSC 35110 377 00155
VCID: 35372233B545BF7F2A1-8060
Subsystem 1 - Part No: 1T2 955 119 A Labels: 1KX-955-119.CLB
Component: Wischer 03121 26 0512
Coding: 009795
Subsystem 2 - Part No: 7N0 951 171
Component: DWA-Sensor 00 002 0205
Coding: 000000
Subsystem 3 - Part No: 1K0 951 605 C
Component: LIN BACKUP HO H05 1501
Coding: 000000
1 Fault Found:
00526 - Brake Light Switch (F)
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 2
Fault Frequency: 11
Reset counter: 102
Mileage: 112427 km
Time Indication: 0
Date: 2014.02.23
Time: 19:47:31
Freeze Frame:
Term 15 On
Voltage: 11.85 V
ON
ON
OFF
OFF
OFF

[Crasher]

Look at the voltage figures stored at the time of error.

[AudisportUK]

I know under 1 volt, does that mean at the switch or at the ECU? Or both?

I can see J757 powers clutch switch, ecu and fuel pump related stuff, but then cant see a link to the brake light switch, I don't know if I fully understand the wiring diagrams and keep looking through relay circuits thinking "that must be it" then convince myself otherwise.

The voltage looks low on terminal 15 too but the battery is a 4 year Bosch under 6 months old and flies the engine over when it starts, which it usually does)

I need to print the diagrams at work tomorrow as navigating through them on the laptop is a nightmare.

thanks
Phil

[Crasher]

I am at work now so I will take a look at the wiring diagram at lunch.

[AudisportUK]

Managed to get VCDS on the van whilst it was in a non start situation today. Same symptoms as last time, practically zero volts at terminal 30 in ECU module, Clutch switch not registering in measuring blocks when pressing, no fuel pump prime.

Checked various readings brake light switch OK from the Central electrics perspective, terminal 30 over 12v in central electrics.

After what I said in post above about possibly being J757 relay, I opened the engine bay fuse box, had the laptop on top of the engine, under 1v terminal 30 (ECU) knocked on the top of the “100 relay” in there, terminal 30 ECU voltage straight to >12v. Starts up no problem after.

I will get a new and hopefully this annoying fault will go away