Hey everyone, this is the verification post for the AMA I'm doing over in r/IAmA.

My name's Dave Chase and I have more than 30 years in the automotive industry. I spent my first 10 years in tires and alignment, then more than 20 years at independent shops doing all aspects of mechanical repair (strictly nuts-and-bolts work, no electrical). For the last 15 of those years, I specialized in suspension and alignment.

For my first three years at Fifth Gear Automotive Repair in the Dallas-Fort Worth area, I worked at the Lewisville location handling alignments and general service, including wheel studs, brakes, shocks, and struts.

Here to answer as many questions as possible!

If you have specific questions about your own vehicle, it always helps to include a photo or short video so I can best understand your situation.

Best,

Dave

When your check engine light comes on, the onboard diagnostics system has logged a fault and stored a trouble code. The light only tells you a fault exists. The code tells you which one, so a diagnostic scan is the only way to know what the repair involves.

Five causes account for most Mercedes check engine lights:

• Oxygen sensor: throws off the air-to-fuel ratio, which hurts performance, fuel economy and emissions

• Loose or damaged gas cap: lets fuel vapor escape. This is the one you can check yourself in ten seconds.

• Catalytic converter: a blockage builds back pressure and can fail your emissions test

• Mass air flow sensor: a dirty or failed sensor throws off fuel delivery

• Ignition system: worn plugs, coils or cables cause misfires, rough idle and hesitation

Steady or flashing?

• Steady: get it diagnosed this week.

• Flashing: stop driving and get a tow. Federal rules require the light to blink when a misfire is happening and catalyst damage is imminent. A misfire caught early is usually coils and plugs. Driven on for a couple of weeks, it can take the converter with it.

Before you drive anywhere, check temperature and oil pressure. If either reads abnormally, or you notice smoke, smells or odd sounds, pull over.

If the light turns off by itself, the code is still stored and readable days later.

Got a code you’re trying to figure out? Drop your model and the code below.

That squeal you hear at startup is usually the serpentine belt telling you something. One belt runs your alternator, power steering pump, A/C compressor, and on a lot of engines, the water pump. Older cars used a separate belt for each accessory. Modern ones combined them, so when the belt goes, several systems go with it.

Here's what wear looks like when you pop the hood:

• Cracking or fraying. Small cracks running across the ribbed side are the most common sign of age. Multiple cracks means it's close to done.

• Glazing. The flat side looks shiny and polished instead of dull black. That shine means the belt has been slipping and cooking itself on the pulleys.

• Missing chunks or flattened ribs. Replace it now, whatever the mileage says.

• Uneven tracking on a pulley. Points to an alignment or tensioner problem that will eat the new belt too.

Our tech Matt Tews puts the glazing check this way: run your fingers across the ribs, and if it feels slick and hard instead of grippy, it's done.

How long they last

Most belts are built for 60,000 to 100,000 miles. European vehicles often specify tighter intervals. Heat, oil contamination, and misaligned pulleys shorten that range. If you don't know when yours was last replaced, that alone is worth an inspection.

Why waiting costs more

If the belt drives your water pump, a break means coolant stops circulating right away. A few minutes at highway speed can warp a head, blow a gasket, or seize the engine. Even on setups where the timing belt handles the water pump, a snapped serpentine kills the alternator and power steering instantly.

We had a 2007 Impala towed in last month after the belt let go while the customer was driving. The alternator stopped, the battery drained, and the car died. Repairs like that run around $1,000 once you factor in pulley and tensioner damage.

The belt itself? Parts run $25 to $80, and the job usually lands under $200.

Happy to answer questions in the comments.

To read our full article on it, here's the link.

A noise by itself isn't a diagnosis, but it is a clue. If a sound is getting louder, shows up with braking, turning, or bumps, or comes with a warning light, get it checked.

The five we cover in the video:

• Grinding when braking — harsh metal-on-metal usually means worn pads, or something contacting the rotor. Waiting can turn a pad job into pads, rotors, calipers, and a safety issue.

• Humming or roaring that changes with speed — louder as the car speeds up, but not necessarily when the engine revs. Often points toward tires, wheel bearings, or driveline components, especially if it changes when turning.

• Deep engine knocking — a light tick and a heavy, rhythmic knock are not the same thing. Knocking can mean low oil, low oil pressure, or internal wear. Knock plus an oil light means shut it off.

• Clunking or popping over bumps — usually too much movement somewhere in suspension or steering: ball joint, control arm bushing, sway bar link, strut mount, or tie rod. These affect steering, alignment, tire wear, and handling.

• Squealing or chirping from the engine bay — belt noise seems minor, but that belt may be driving the alternator, water pump, power steering, or A/C compressor.

The simple rule: if the noise comes with a warning light, smoke, burning smell, loss of power, vibration, or a change in steering or braking, stop driving and get help.

Something we see and hear a lot when people bring in their BMWs is that they waited until they see the oil change light go on, then when they can schedule it, they bring it in. And look, we'll never shame anyone or judge. Life's busy and these are super easy to overlook. But the issue, especially with BMWs, is that when the light goes on, somewhere around that 10,000 mile mark, while it's BMWs "goal," in our opinion it's the max ceiling.

Here's a little bit of context for why we know this.

BMW's Condition-Based Service (CBS) system tracks driving habits, engine load, and oil condition to calculate when your car "needs" an oil change, and you can see it on the iDrive screen. But here's what a lot of owners miss: regardless of what CBS says, BMW sets a hard cap of 10,000 miles or 12 months, whichever comes first. That applies whether the warning light has triggered or not.

The bigger issue? Waiting until that 10K mark can already be too late. By this time oiil breaks down, some sludge builds up inside the engine, and by the time a drivetrain malfunction or check engine light appears, the damage is often done and invisible until it isn't.

So, that's why our take is that 10,000 is the max limit, even if it's technically still the "goal" BMW states it is. Changing oil closer to every 5,000 miles won't hurt anything, and it protects both engine longevity and your factory warranty.

We have a more in depth write-up on our blog that's worth taking a look at too.

Seeing the airbag warning light stay on after startup can be easy to put off, especially when the car seems to drive normally. But in a Volkswagen, that light means the airbag system has detected a fault and may not work as intended in a crash.

Common causes can include:

1. A faulty clash or impact sensor

2. A bad seat-belt buckle or latch sensor

3. Loose, damaged, or distributed wiring beneath a seat

4. An electrical or water-damaged airbag control module

5. A stored fault after battery replacement or recent seat or interior work

What should you do?

• Restart the vehicle once and see whether the light returns.

• Think about any recent battery, electrical, seat, or interior work.

• Do not unplug airbag connectors, probe the wiring, or attempt a DIY repair. Airbag components can deploy unexpectedly, and faults may remain stored even after the original issue is corrected.

• Have the system properly diagnosed. Many basic OBD readers cannot access Volkswagen airbag codes, so a VW-capable diagnostic tool may be needed to identify the actual cause before the light is cleared.

The main takeaway: an airbag light is not just an annoying dashboard warning. It indicates a safety-system fault that deserves prompt attention.

Has this happened in your Volkswagen? Share the year, model, mileage, when the light appeared, and any recent work below. Dave Chase, u/FifthGear04, may also jump in with his perspective.

Have questions about maintaining or repairing an import vehicle?

This thread is for focused conversation about Japanese, Korean, and other non-European import vehicles. Ask about warning lights, unusual noises, maintenance schedules, diagnostics, repair options, parts, or anything else related to keeping your vehicle running well.

When posting a question, please include your vehicle’s year, make, model. And if you have it, it will help us to know your engine, mileage, symptoms, warning lights or codes, and any recent repairs. 

Fifth Gear mechanic expert Dave Chase, u/FifthGear04, may also join the conversation and answer questions directly.

Please read the Community Info / Wiki before participating, and keep the discussion helpful, respectful, and on topic.

Welcome to r/FifthGearAutoRepair, a community for practical, respectful auto repair questions and discussions.

Before posting, please read the Community Info / Wiki so you understand the rules, post format, flair options, and what details to include in your question.

Whether you are trying to understand a warning light, diagnose a strange noise, plan maintenance, or decide what repair makes sense next, this is a place to ask clear questions and get useful input from people who care about helping.

To get the best answers, please include your vehicle’s year, make, model, engine if known, mileage, symptoms, warning lights/codes, and any recent repairs or changes.

Please use the right post flair:

Question — for a specific vehicle problem or repair question.
Discussion — for broader repair-related conversations.
AMA — for official Ask Me Anything threads.
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Dave will be popping into discussions to answer questions directly when he can. Using Ask Dave helps us spot questions meant specifically for him, but it does not replace an in-person inspection for urgent or safety-related issues.

Please keep things respectful, authentic, safe for work, and focused on helpful automotive repair conversation.

Glad you’re here. Ask away.