At BMW Car Service North Shore, we have a lot of admiration for BMW’s brilliant X series, a four-wheel drive that combines excellent off-road ability with sporty performance and luxurious interior refinement. It really must be one of the most desirable SUV’s on the market, loved by owners and professional mechanics alike.

Even the Reliable BMW X Series Has Occasional Mechanical Issues

One of our customers is fortunate enough to own both a BMW X6 and its smaller sibling, the X3. Less fortunately, the cars simultaneously developed different faults and both ended up being brought to BMW Car Service North Shore for diagnosis and repair.

Investigating Warning Lights and Carrying Out a Full Service on the BMW X6

First to roll into the workshop was the customer’s late model BMW X6 Xdrive 50i, which had three straightforward jobs for our specialist BMW mechanics to carry out:

  1. Complete a full maintenance service
  2. Answer brake warning light
  3. Diagnosis of faulty driver’s side parking light

We received a little more detail from the owner, who mentioned that the driver’s side parking light had been working intermittently for some time and that the ‘bulb out’ warning on the BMW’s instrument cluster had been sporadically flashing but was now constantly on.

Our mechanics completed the full vehicle service and replaced the rear brakes, which quickly resolved both the ‘service due’ and ‘brake warning’ light issues.

Diagnosing and Resolving a Parking Light Issue

Next, our mechanics checked the globe in the righthand side driving light, only to discover a 55w globe had been fitted, instead of the manufacturer-recommended 35w version. On replacing the 55w lamp, we tested for power and found none present but two grounds (meaning a short-circuit to ground). We had no idea why the wrong globe had been used in the first place but realised that there was a reasonable chance that that this action had caused the short.

We then examined the BMW’s X6’s wiring diagram, to see if there were fuses to the light (there weren’t). The wiring is meant to go through a single connector straight to the FRM (Foot-Well Module) that powers the left-side driving light.

Next our technicians carried out a scan of control unit FRM and found two faults:

– Right driving light faulty.

– Short-circuit in FRM.

On testing the light socket, we found ground to both terminals, indicating a short to ground. Next job was to check out the short-circuit. Could it be in the FRM or the wiring, the connectors or perhaps the head lights? Servicing a modern BMW is often like a surgeon diagnosing a patient who comes into casualty with a stomach ache i.e. before deciding to operate it’s prudent to rule out the obvious and ask them if they’ve just eaten some bad seafood!

In this case, we couldn’t reach the headlight connector to test it without stripping the guard liner, and experience told us it was more accessible to remove the FRM for testing. We disconnected the FRM and ran the test. Looking up wiring diagrams, we confirmed pin 14 on X14260 was sending power to the light. We then found the short-circuit with the FRM disconnected, so it didn’t take long to establish, via a process of deduction, that the short-circuit was on the wiring side.

Putting the BMW X6 up on the Hoist for Repair

Next up, we hoisted the vehicle and removed the driver’s side wheel and guard liner, to expose the headlight assembly and gain better access to the headlight connector. We then disconnected the connector and – voila! – we found the short-circuit was cured. Proof positive that the problem was in the headlight itself, not the FRM.

In case you’re wondering why we needed to find the short and make sure the FRM had not been damaged by the short-circuit, it’s because a new FRM costs over $1,000, and without fixing the short, it is at serious risk of being damaged once the car is in motion.

Next up, we ran new wiring to connect the globe straight to the FRM. The FRM has short-circuit fail-safe protection, which had to be reset. We did this through our ‘Autologic Diagnostic System’ and connected it all up. The light was finally working again.

Our Vast Experience with BMW Electrics Saved the Owner Lots of Money

We were glad to know the FRM unit and wiring loom were fully functional and that the short-circuit was in the headlight. To remove this headlight, we would first have had to remove the front bar and the driver’s side guard – approximately 3-4 hours work and more labour costs for the customer to bear. However, since the guard liner was already off and the headlight exposed, we decided to attempt to find the short-circuit and save the customer money by repairing it without removal.

Note: the headlight for a BMW X6 – Xenon model with adaptive headlights – costs $2,562, plus its control unit at $1,310. We’re pretty sure the customer wouldn’t have wanted $3,872 plus labour charge added to their bill!

Bear in mind that the short-circuit was inside the headlight, meaning without its removal and disassembling the headlight front perspex and its assembly, we had very limited room to work with. But with our long experience of working on BMWs standing us in good stead, we managed to remove the main connector from the headlight, de-pin the shorted-out terminal and then run new wiring to the factory pins.

We ran a final globe test prior to re-assembly and it was working perfectly. Needless to say, the owner was over the moon about not having to fork out an extra few thousand dollars! 

BMW X3 E83 Diagnostic and Repair

The following day, BMW Car Service North Shores’s mechanics moved on to the customer’s other car, a BMW X3 E83. It had no operational wipers, no central locking, no headlights, and no working audio system. We didn’t waste any time but quickly scanned the vehicle and found faults with K bus (communication bus for body control) and also noticed that there was no communication with the body module.

Looking up the wiring diagram and the K bus tree, we found all the inoperative components were controlled by the body module. Since there was zero communication with the body module we needed to see if the body module itself was faulty.

We tested the power and ground to the body module and found that to be okay. Next, we connected an oscilloscope to the K bus, to see if there was any signal. We proceed to locate all the modules in the K bus tree, to see exactly which one was corrupting the K bus.

While testing the battery we noticed water in the battery tray. Digging deeper, we discovered that the GPS unit and the amplifier on the left side, adjacent to the battery, had suffered corrosion. After removal of the units and checking the wiring we found major corrosion in the wiring, due to water ingress into the cabin of the car! Water ingress is something we’ve been dealing with a lot lately, due to recent heavy rainfall in Sydney. It’s an easily diagnosed cause of  component damage in un-garaged vehicles.

What we had to do now, after figuring that out, was to dry out the wiring and antennas for the GPS, amp etc., before carrying out one of the most important procedures: coding the body module.

Everything was back online, except for the GPS and audio system. The customer told us to leave both at that time, to save on labour and parts. But they obviously needed the wipers and central locking working again!

BMW X3 Water Ingress Diagnostic

However, it turned out this was only half the battle as we needed to find the source of the leak or else all the problems would come back again, due to more water getting into the vehicle.

We removed some of the interior pieces and hosed down the car to find where the water was intruding, a procedure that can take hours, but fortunately our experienced technicians know BMWs inside out and exactly where to look for the traces.  They soon found that the drains for the sunroof were blocked. They then unblocked them, double-checked them by hosing a few more times, and then reassembled the interior components.

The last job left to do was to re-program the car keys.

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