Welcome to Tech Talk, where our resident BMW tech Nick Owen answers all your pressing BMW technical questions, frustrations, and issues. Have a question for Nick? Email him at techtalk@roundel.org. Let’s get into it.
E46 Cruise Control Issue Follow Up
I wanted to follow up on the cruise control malfunction in my 2004 330i ZHP sedan. I replaced the clutch pedal switch, brake pedal switch, and the steering wheel switches. The cruise control malfunction is different now. The cruise main switch can be turned on during the first 15-20 minutes of driving, but the main will not turn on after 20 minutes. The cruise control will maintain the speed during the first 15-20 minutes of driving, but then it cuts out; the cruise main remains on, but the set button will no longer engage the cruise control. If the car is turned off and back on, the cruise control will work again for a short time. What are your thoughts about possible problems?
Carissa Taeubel
I think it’s time to condemn the module for the cruise control. It’s located behind the glove box (blue connector) and I think it can be swapped out for a used one for easy replacement.
Use of a Plug-In Inverter
I currently have a 2023 X5 M. I would like to plug in an AC/DC inverter using either the cigarette lighter or under the hood battery terminals. I’d be plugging into it a garage door retractable screen, requiring 750 watts to operate when there is a power failure with the garage door in open position. In this situation there is no way to open the screen to get the car out, which would be a nightmare if I needed to, before power restoration.
This has not happened yet but if it did it would only be a 20 second use to open the screen. That’s it. Not used again for who knows how long. “Just a back-pocket precaution”.
Can an inverter be used without damaging the electronics and, if so, do you have any recommendations as to what brand to use? Should the engine be running during that 20 second use? Would there be any significant battery drain?
Steven Moretti
While this scenario is rare, I do not recommend using any kind of inverter on a modern BMW unless it is an absolute emergency and there is no other option. With that said, you’re better off buying a car battery from AutoZone and leaving it by the screen door with an inverter in case of this scenario happening. Leave the X5M out of the equation entirely.
The amperage needed to move 750 watts is going to be about 65 amps, and most vehicle electrical systems (interior components) are fused to 40 amps max. Therefore, you shouldn’t use a cigarette lighter to power the inverter, you’re better off going directly from the battery. The electrical systems in these modern cars can be sensitive to outside voltage accessories. I would contact the manufacturer of the screen door and ask what they would recommend in case of a power failure.
325i (E30) and 2015 X5 (F15) Diesel
I have a 1988 325i convertible, and my windshield wiper no longer operates. I replaced the fuse (30-amp, No. 5), which keeps frying as soon as I try to operate the wiper. The car also has a vampiric drain issue (related to the wiper issue?). Where do I start with both? Finally, when the gas tank is full, there is a strong odor of gasoline, and some leakage. What could this be due to?
My other BMW is a 2015 X5 Diesel. The sunroof leaks into the passenger compartment out of the insert in the headliner that appears to be a microphone, but only on the passenger side. I have tried clearing the drains in the sunroof with compressed air as well as a weed trimmer plastic line, without success. Any hints before I take a huge step and remove the headliner and try to detach and clear the correlated tubes or remove the left front fender and try to clear the tube from below?
Scott P. McBride
I’ve broken down your questions below:
My windshield wiper no longer operates. If the fuse is blowing, then that means there is an electrical short. It could be in the wiring for the wiper motor, or the wiper motor itself. My gut says the wiper motor has failed internally. Try replacing that.
The car also has a vampiric drain issue. This one can be tough to diagnose. I doubt the wiper motor fuse issue is related, however it would be wise to address that issue first. Parasitic draws are diagnosed with an amp meter and amp clamp to see if a component is switched on after the vehicle has been shut off. I don’t have a way of helping with this over email other than I recommend seeking professional help.
When the gas tank is full, there is a strong odor of gasoline, and some leakage. If you only smell fuel when the gas tank is full, then the seal at top of the tank is probably leaking. I think you can access the top of the fuel tank from the trunk. I recommend filling the car up full to diagnose the source of the smell, then perform the repair once the tank is nearly empty to help reduce spillage.
The sunroof leaks into the passenger compartment. Remove both front A-pillar covers and both rear C-pillar covers. You should be able to access the drain tubes at each corner. Take the rubber hose tubes off and pinch them around a compressed air nozzle. Then use compressed air to clear the drains. This is how we did it on E60 models as well as E70. Be very careful removing the A-pillar covers as there can be tension built in the base that will snap into the windshield and crack it. I use my one hand at the bottom to prevent it from snapping while I use my other hand on top of the cover to wiggle it up and out of the dash. Be patient here, but it will come out.
Engine Oil for 2026 M2
I checked on BMW approved full synthetic oils for the engine and saw that Castrol 0-30 wt. And Mobil 1 0- 40 wt. are both recommended. It would seem with the heat of two turbos even for normal every day driving the Mobil 1 would offer better long-term engine protection.
I usually lean toward what the manufacturer recommends, but I also know that some manufacturers recommend thinner weight oils to meet fuel economy standards. What do you recommend?
Russ DeJulio
You’ll be fine with 0w-30. Considering your local climate, thinner will be ideal.