BCM fault affecting indicators, brakes, wipers, windows and boot
Posted: Mon Aug 10, 2026 10:38 am
Hi everyone,
I am looking for help with a very strange intermittent electrical fault on a left-hand-drive 2010 Polo 6R 1.2 TDI CFWA with Start/Stop and halogen headlights.
BCM history and how the problem started
The car was built in May 2010, but when I started investigating it, it did not appear to have its original BCM fitted. The BCM in the car had a part number ending in D and its date did not seem to match the car, being roughly four or five months away from the vehicle build date. ETKA says that the correct BCM for this car should have a part number ending in F.
The first faults started randomly with the suffix D BCM. The indicators would operate by themselves or stop responding, the boot release and Start/Stop would stop working, and the brake lights behaved incorrectly. During the original version of the fault, the brake lights could remain permanently on even when the pedal was not being pressed.
That BCM was replaced with another unit ending in D, but the fault eventually returned. With that replacement D unit, the main implausible-signal problem appeared to turn light switch.
Before fitting the correct suffix F BCM, I completely removed a badly installed towbar control module and its added wiring. It had been connected into the rear lights, brake signal and CAN wiring. I repaired the points where it had been connected, although I am still checking these repairs and the original loom for hidden damage.
The currently fitted BCM is the suffix F unit which ETKA says is correct:
6R0 937 088 F
BCM PQ25 Re4, H50 0351
Coding: 22B02BBF08A10000003009B06E2B0CD05F80612F7E860441200000000000
What happened after fitting the correct F BCM
After fitting this BCM, everything worked normally. I drove about 30 km without any faults, then parked and left the hazard warning lights switched on for about 30 minutes while I was away. I returned and drove for another 10 minutes, then switched the car off normally and left it for about one hour. I later drove another 30 km home, again with no apparent problem.
When I arrived home, I started removing tools from the front passenger area and the boot. At that point, the indicators suddenly began flashing by themselves and the fault returned. This means the replacement BCM had worked correctly for roughly 60–70 km, including a one-hour rest and a period with the hazards operating, before the problem returned while I was moving things inside the car and boot.
The fault now seems slightly different from the original one. Originally, the brake lights could remain permanently on. This time, none of the brake lights work at all. The electric windows now also appear not to work.
Current symptoms
- The indicators can flash by themselves or stop working completely. Neither the hazard switch nor the indicator stalk can operate them when the fault is active.
- None of the brake lights work. This is the opposite of the original fault, when they could remain permanently on.
- The front windscreen wipers do not work.
- The electric windows now appear not to work.
- The exterior boot handle does not work. The remote could initially open the boot, but that has now also stopped, although I can still hear a relay operating.
- The interior central-locking button does not work.
- Start/Stop and cruise control do not work.
- The BCM/J519 reports Terminal 15 as off even though the ignition is on.
Moving or closing the boot has sometimes changed the indicator behaviour. This still makes me suspect the boot loom, rear earths, disturbed wiring or the remains of the old towbar installation.
I have now tried the BCM originally fitted to the car and two replacement BCMs. The same general problem has returned with all three, usually after driving 30–50 km or after the car has been operating normally for some time. This makes me think the real cause is outside the BCM.
Main faults from the latest VCDS scans
Engine, address 01:
- 14106 / 14108 – P0568, Cruise Control Switch E45, implausible signal.
- In the engine freeze-frame data, Terminal 15 was shown as ON and system voltage was about 13.5 V.
Central Electrics/BCM, address 09:
- 01365 – interior lock/unlock switch, implausible signal.
- 03297 – driver’s door lock-cylinder switch, implausible signal.
- 00893 – boot-handle switch E234, implausible signal.
- All three BCM faults were recorded at exactly the same time, although the switches are in different parts of the car.
Battery Regulation, address 61:
- 00458 – no communication with battery monitor J367.
- 02252 – no communication with generator.
- An earlier scan also had 02071 – local data bus, electrical fault.
- J367 and the generator faults were recorded at exactly the same time.
This seems important because the earlier replacement D BCM mainly showed an implausible Terminal 15 signal, while the correct F BCM now records three different implausible switch signals. At the same time, the engine ECU records the cruise-control implausible-signal faults.
There were also instrument-cluster communication faults, but some of those were caused while parts were being disconnected during testing, so I am not treating those as the main fault yet.
Areas I plan to check
- The permanent supply shared by the BCM and Gateway. The wiring diagram calls the hidden loom joint B111. It feeds BCM pin T73b/39 and Gateway pin T20a/1.
- BCM earth T73b/38, which goes to earth point 606 under the centre console.
- The BCM’s own Terminal 15a input at T73a/44 and its fuse/ignition-switch route.
- The boot loom, boot-handle switch, lock unit and rear earth point 61.
- The repaired CAN, brake-signal and rear-light wiring from the removed towbar installation.
- The local LIN communication wire between the Gateway, battery monitor J367 and alternator regulator.
The two 73-pin BCM connectors are sealed and protected. I cannot safely back-probe them with the BCM connected, and I do not want to pierce the insulation or damage the terminals.
Questions
1. Is the shared BCM/Gateway permanent supply or earth point 606 a known problem area?
2. Can a shorted J367 or alternator LIN wire disturb the Gateway enough to cause these body-electrical symptoms, or is that probably a separate fault?
3. Are there known failures in the boot loom or rear earths which can make the indicators operate by themselves and create several implausible-switch faults together?
4. Which VCDS measuring blocks are most useful for watching Terminal 15, boot handle, locks, indicators, brake and wiper inputs on this BCM?
5. What is the safest way to test the BCM supplies and outputs under load without damaging the sealed connectors?
6. Does the change from one implausible Terminal 15 fault with the D BCM to three simultaneous implausible switch faults and P0568 with the F BCM suggest a shared supply, earth, reference or wiring fault?
7. Could the fact that the fault returned while I was removing tools from the passenger area and boot point to a disturbed loom or earth connection?
I can post the complete Auto-Scan, photos of the towbar-wiring repairs and any live measurement results. I would like to prove the power supply, earths, ignition signal, CAN, LIN and rear loom before fitting another BCM.
Thanks for any help.
I am looking for help with a very strange intermittent electrical fault on a left-hand-drive 2010 Polo 6R 1.2 TDI CFWA with Start/Stop and halogen headlights.
BCM history and how the problem started
The car was built in May 2010, but when I started investigating it, it did not appear to have its original BCM fitted. The BCM in the car had a part number ending in D and its date did not seem to match the car, being roughly four or five months away from the vehicle build date. ETKA says that the correct BCM for this car should have a part number ending in F.
The first faults started randomly with the suffix D BCM. The indicators would operate by themselves or stop responding, the boot release and Start/Stop would stop working, and the brake lights behaved incorrectly. During the original version of the fault, the brake lights could remain permanently on even when the pedal was not being pressed.
That BCM was replaced with another unit ending in D, but the fault eventually returned. With that replacement D unit, the main implausible-signal problem appeared to turn light switch.
Before fitting the correct suffix F BCM, I completely removed a badly installed towbar control module and its added wiring. It had been connected into the rear lights, brake signal and CAN wiring. I repaired the points where it had been connected, although I am still checking these repairs and the original loom for hidden damage.
The currently fitted BCM is the suffix F unit which ETKA says is correct:
6R0 937 088 F
BCM PQ25 Re4, H50 0351
Coding: 22B02BBF08A10000003009B06E2B0CD05F80612F7E860441200000000000
What happened after fitting the correct F BCM
After fitting this BCM, everything worked normally. I drove about 30 km without any faults, then parked and left the hazard warning lights switched on for about 30 minutes while I was away. I returned and drove for another 10 minutes, then switched the car off normally and left it for about one hour. I later drove another 30 km home, again with no apparent problem.
When I arrived home, I started removing tools from the front passenger area and the boot. At that point, the indicators suddenly began flashing by themselves and the fault returned. This means the replacement BCM had worked correctly for roughly 60–70 km, including a one-hour rest and a period with the hazards operating, before the problem returned while I was moving things inside the car and boot.
The fault now seems slightly different from the original one. Originally, the brake lights could remain permanently on. This time, none of the brake lights work at all. The electric windows now also appear not to work.
Current symptoms
- The indicators can flash by themselves or stop working completely. Neither the hazard switch nor the indicator stalk can operate them when the fault is active.
- None of the brake lights work. This is the opposite of the original fault, when they could remain permanently on.
- The front windscreen wipers do not work.
- The electric windows now appear not to work.
- The exterior boot handle does not work. The remote could initially open the boot, but that has now also stopped, although I can still hear a relay operating.
- The interior central-locking button does not work.
- Start/Stop and cruise control do not work.
- The BCM/J519 reports Terminal 15 as off even though the ignition is on.
Moving or closing the boot has sometimes changed the indicator behaviour. This still makes me suspect the boot loom, rear earths, disturbed wiring or the remains of the old towbar installation.
I have now tried the BCM originally fitted to the car and two replacement BCMs. The same general problem has returned with all three, usually after driving 30–50 km or after the car has been operating normally for some time. This makes me think the real cause is outside the BCM.
Main faults from the latest VCDS scans
Engine, address 01:
- 14106 / 14108 – P0568, Cruise Control Switch E45, implausible signal.
- In the engine freeze-frame data, Terminal 15 was shown as ON and system voltage was about 13.5 V.
Central Electrics/BCM, address 09:
- 01365 – interior lock/unlock switch, implausible signal.
- 03297 – driver’s door lock-cylinder switch, implausible signal.
- 00893 – boot-handle switch E234, implausible signal.
- All three BCM faults were recorded at exactly the same time, although the switches are in different parts of the car.
Battery Regulation, address 61:
- 00458 – no communication with battery monitor J367.
- 02252 – no communication with generator.
- An earlier scan also had 02071 – local data bus, electrical fault.
- J367 and the generator faults were recorded at exactly the same time.
This seems important because the earlier replacement D BCM mainly showed an implausible Terminal 15 signal, while the correct F BCM now records three different implausible switch signals. At the same time, the engine ECU records the cruise-control implausible-signal faults.
There were also instrument-cluster communication faults, but some of those were caused while parts were being disconnected during testing, so I am not treating those as the main fault yet.
Areas I plan to check
- The permanent supply shared by the BCM and Gateway. The wiring diagram calls the hidden loom joint B111. It feeds BCM pin T73b/39 and Gateway pin T20a/1.
- BCM earth T73b/38, which goes to earth point 606 under the centre console.
- The BCM’s own Terminal 15a input at T73a/44 and its fuse/ignition-switch route.
- The boot loom, boot-handle switch, lock unit and rear earth point 61.
- The repaired CAN, brake-signal and rear-light wiring from the removed towbar installation.
- The local LIN communication wire between the Gateway, battery monitor J367 and alternator regulator.
The two 73-pin BCM connectors are sealed and protected. I cannot safely back-probe them with the BCM connected, and I do not want to pierce the insulation or damage the terminals.
Questions
1. Is the shared BCM/Gateway permanent supply or earth point 606 a known problem area?
2. Can a shorted J367 or alternator LIN wire disturb the Gateway enough to cause these body-electrical symptoms, or is that probably a separate fault?
3. Are there known failures in the boot loom or rear earths which can make the indicators operate by themselves and create several implausible-switch faults together?
4. Which VCDS measuring blocks are most useful for watching Terminal 15, boot handle, locks, indicators, brake and wiper inputs on this BCM?
5. What is the safest way to test the BCM supplies and outputs under load without damaging the sealed connectors?
6. Does the change from one implausible Terminal 15 fault with the D BCM to three simultaneous implausible switch faults and P0568 with the F BCM suggest a shared supply, earth, reference or wiring fault?
7. Could the fact that the fault returned while I was removing tools from the passenger area and boot point to a disturbed loom or earth connection?
I can post the complete Auto-Scan, photos of the towbar-wiring repairs and any live measurement results. I would like to prove the power supply, earths, ignition signal, CAN, LIN and rear loom before fitting another BCM.
Thanks for any help.
, I have to fix some DTCs on my Leon 1P with the MIB2 retrofit, and now I also have a Smart 454 that could probably go straight to a scrapyard, but somehow I like it 