Thread: 03 D2a TD5 automatic transmission - intermittent reverse lights

No separate switch, does the "R" on the dash show when you have no reverse lights?

Originally Posted by discorevy

No separate switch, does the "R" on the dash show when you have no reverse lights?

Yep, have R on the dash next to the odometer.

Both reverse lights are out. Gloves work fine. If no seperate switch then maybe a blown fuse for the lights but that wouldn’t explain its intermittent nature...

Have you checked the bulbs?

Regards Philip A

Originally Posted by PhilipA

Have you checked the bulbs?

Yes, I have swapped in tested known working globes from the rear fog lights and still no change. Have also tested the removed reverse light globes into the fog lights and they worked.

But my issue is more complex than that as the reverse lights are the trigger for the rear view camera and a secondary LED reverse light mounted on the roof rack which are not working either. I’m particularly concerned about the lack of reverse camera as I work at a school and the Disco with lift and all the gear on it can easily hide a child behind...

I pulled the multimeter out and tested Fuse 25. Also tried a different fuse in there. It has power. Therefore the issue is later in the line.

Assuming that since the dash has an R on it and the gearbox is going into reverse and reversing fine it is either an issue with the BCU or a break in the line.

Wiring diagram on Rave says that it goes through the following connectors hat I will now need to locate and check:
295
294
668
681
675
586

According to Rave:

When the reverse lamp switch is operated, the switch contact closes and allows current flow on a GN wire, from the switch, through two headers C0287 LHD/C0294 RHD and C0295, to the RH reverse lamp and the LH reverse lamp. The LH reverse lamp is earthed on a B wire to earth header C0707. The RH reverse lamp is earthed on a B wire to earth header C0706.
When the reverse lamps are on, a splice joint A13 between headers C0287 LHD/C0294 RHD and C0295, gives a feed on a GN wire to the interior mirror.
The feed supplied to the interior mirror will change the interior mirror to the undipped condition, if the interior mirror is dipped. The interior mirror will remain in the undipped condition as long as a feed is supplied. This feature ensures that the interior mirror is in the undipped condition when reverse gear is selected.
A GN wire from header C0287 LHD/C0294 RHD is connected to the BCU. When the reverse lamp switch is operated, this feed is used by the BCU logic circuits to enable rear wiper operation.

My next step will be to test for this signal.

Finally got a few minutes to investigate with a multimeter. What I have found is that:

There is power going from Fuse 25 through to Connector 668-2. From here it connects to 681 and the wiring loom goes to the XYZ switch on the automatic transmission and back.

If I jumper 668-2 and 668-1 together the reverse lights and camera turn on immediately. This indicates to me that there is no issue with the lights, camera, power supply or other wiring looms. Therefore the issue is isolated to either the XYZ Switch and/or the wiring loom to/from it (connector 681 to 675). It was only July last year that I removed the XYZ Switch and it's wiring loom due to chaffing in the loom < Auto M + S Error Code P0705 Position Switch Monitoring caused when underbody wet > While problem solving I opened up the XYZ switch, cleaned it and resealed it.

EDIT: found a bit more time and disconnected Connector 675 from the XYZ switch. Using a jumper between pins 1 and 2 immediately turns on the Reverse lights every time. Therefore I conclude it is my XYZ switch that has the issue. Seems trying to fix my issue last year compromised it and lead to this issue now...


What I cannot understand is that the dash always know when the car is in reverse. It has an R on the dash. Even with the reverse lights not working. How does it know this? Is this signal provided to the dash from the gear selector (i.e. is there a sensor on the interior gear selector shifter mechanism that is telling the dash that it's in reverse?)? According to the wiring diagram the signal to the BCU for Reverse is from Connector 294 which is downstream of the XYZ switch (i.e. therefore the BCU wouldn't get this signal either when the reverse lights aren't working).

In theory there is the possibility that the reverse contact in the switch is weak or in that 675 plug and the voltage drops under the bulb's load while for the BCU is enough even 6V to show that R while the bulbs are not working with that, remove both bulbs and measure for voltage in the holder with R selected cos the voltmeter has no load and if it's that you'll see the voltage then fit back one bulb and see the drop eventually measure with both bulbs in if you see what i mean...btw are the brake lamps working? to rule out bad earth at both clusters, quite unlikely but possible so if it's facelift measure voltage against body too

Originally Posted by sierrafery

btw are the brake lamps working? to rule out bad earth at both clusters, quite unlikely but possible so if it's facelift measure voltage against body too

Not sure, will get a second person to push so that I can check.


I removed the XYZ inhibitor switch and opened it up. It was sealed well and inside all clean. No obvious issues. Moved the cam wheel through it's revolution and it seemed to operate fine. In the reverse position the microswitch was operated and closed the circuit. Maybe it was just out of it's alignment in the mounting to the gearbox?

What I did realise is that there is no relay for the reverse lamp circuit. It has a 15amp fuse and this power is all going straight through the XYZ switch. A friend gave me his old faulty switch which upon opening it seems to be an aftermarket knock off cheaper version of the ZF genuine part:




The tab for the reverse lamp connection in this one is visibly much darker to all the other copper, possibly due to all the amp draw going through it to make the reverse lights work.

I'm going to ad a relay in under the centre console so that the XYZ switch output acts as the trigger. This will take the load off it and maybe that's all that's required to get one of these two operating reliably again. Tomorrows job to find out.