Auto Parts Quality Checklist: What to Check Before You Install a Headlight, Strut, or Bushing

I'm a quality and brand compliance manager for an auto parts supplier. I review new product samples, batch stock, and warranty returns before they go any further. It's roughly a few hundred components a year, mostly aftermarket lighting, suspension, and engine service parts. This is the four-check routine I recommend before you install a part from a shipment. It takes about ten minutes and it catches most of the problems that later turn into comebacks.

This checklist is meant for aftermarket toB buyers and workshop technicians who want a quick check on the bench. It is not a substitute for the vehicle-specific workshop manual, and it won't tell you which brand is 'the best.' No such thing. It tells you whether the part you are holding is likely sound.

When to Use This Checklist

Use it when you receive new stock, before you install a part that has been in storage, or before you file a warranty claim for a part that doesn't behave. Four checks, five to ten minutes. If a part fails any of them, don't install it. Send it back before it costs you an hour of labor and a second repair.

Check 1: A Hella LED Headlight Needs More Than a Bright Beam

The first thing I inspect on a new headlight is not how white the beam looks on a wall. It's the approval mark and the part identity. Suppose you ordered a Hella LED headlight to replace an old round reflector unit. I look at the lens or housing for a visible type-approval mark. If there's no visible mark, only a printed label on the box, that's a red flag for road use. A label can be stuck on anything. The mark on the housing stays with the part.

If the part is a Hella 7 inch headlight, I also check the beam orientation and the voltage before anything else. A 7 inch round housing is common on older 4x4s and commercial vehicles, but '7 inch' alone doesn't tell you whether it's the correct beam pattern for your market. Left-hand traffic and right-hand traffic versions are not always interchangeable for LED units. And if the vehicle uses a sealed-beam-style connector, the plug should fit firmly. A lot of 'flickering headlight' complaints I review end up being a loose or corroded connector, not a faulty lamp. Check the terminals first. A Hella 7 inch headlight that flickers on low beam only is often just a tired original plug that doesn't grip the new pins properly.

1. Part number on the label matches the delivery note.
2. Approval mark is visible on the lens or housing, not only on the box.
3. Connector pins are straight, the plug seats firmly, and the housing has no cracks or moisture inside.

Check 2: OKRA Strut or Any Strut, Stroke It Before You Install It

Suspension parts get damaged in transit more often than people expect. If the delivery includes an OKRA strut, or any other damper, I don't trust the box. I check the rod first. A bent or nicked piston rod will destroy the shaft seal within a few hundred kilometers, even if the strut looks fine at first glance.

Run your hand carefully along the exposed part of the rod, from the top down to the boot. If the rod has a thread on top, check that too. A damaged thread can still clamp down, but it will give you a false torque reading, and that's how strut nuts come loose later.

Then stroke the strut. Hold it upright and compress the rod slowly, then let it extend. On a gas-charged strut, you should feel smooth, continuous resistance and the rod should push back on its own. It should not pop, jerk, or have a dead spot in the middle of the stroke. If it feels inconsistent after three or four full strokes, don't install it.

One honest caveat: this check tells you about condition, not ride comfort. A new strut can feel stiff until the seal wets itself, and different brands have different damping curves. What I'm looking for is damage and inconsistency, not 'feel.' I'm not a suspension tuning specialist, and I don't pretend to be one. But a strut that fails a basic stroke test will not improve once it's on the car.

1. Piston rod is straight, smooth, and free of nicks or rust.
2. Strut compresses and extends with smooth resistance, no sticking or knocking.
3. No oil streaming from the rod seal. A light film of assembly oil is normal; a wet rod after wiping is not.

Check 3: Pull the Correct Control Arm Bushing Diagram First

When it comes to control arm bushings, most of the returned parts I see didn't fail. They were installed incorrectly. The bushing itself is fine. It was twisted or preloaded during installation, and it failed early because of that.

Before you remove anything, get the correct control arm bushing diagram for that specific vehicle and kit. Some bushings are offset, which means they are not symmetrical. The diagram shows which side faces the front of the vehicle and where the arrow or line on the rubber should point. Ignoring that arrow is how you get a bushing that looks perfect in the press but sits twisted once the arm is bolted in.

There is one step that almost everyone skips, and it's the one that causes the most comebacks: final torque. If you tighten the control arm bolts while the suspension is hanging in the air, the bushing is preloaded. The car rolls out of the shop feeling fine, then within a few hundred kilometers you get vibration, harshness, and a bushing that looks like it failed from the inside. The fix is simple. Lower the vehicle to normal ride height, let the suspension settle, and then torque the bolts to spec. If you followed the control arm bushing diagram but skipped this step, you still did it wrong.

1. Compare the new bushing orientation marks to the control arm bushing diagram before pressing.
2. Press the bushing in square with the correct support cup. Never hammer it in.
3. Final torque is done at ride height, not with the arm hanging free.

Check 4: Can You Clean the Throttle Body with Brake Cleaner?

This question comes up all the time, so let me give you a straight answer. Can you clean the throttle body with brake cleaner? Physically, yes. It will remove carbon quickly, and it works in a pinch. The longer answer, from the quality side, is that I don't recommend it, and I won't approve it as a standard procedure.

Here's why. Many modern throttle bodies have a dry-film coating on the bore and throttle plate that helps reduce carbon buildup and keep the plate moving smoothly. Brake cleaner is aggressive. It can strip that coating. You won't see the damage immediately, but the carbon will come back faster, and the throttle plate may start sticking or idling rough later. Brake cleaner is also not formulated to be gentle on plastic gears, shaft seals, or electronic throttle actuators. It's made for brake parts, not for a drive-by-wire module that sits right next to the intake.

If you already used brake cleaner once and nothing happened, that's fair. Some all-metal throttle bodies survive it. But 'it didn't fail that one time' is not a quality procedure. Use a cleaner that's labeled safe for throttle bodies and oxygen sensors. The price difference is small, and the risk is unnecessary.

If you do decide to clean the throttle body, do it this way:

1. Start with a cold engine. Disconnect the intake duct and the electrical connector. Never spray cleaner into a running engine.
2. Use a cleaner labeled for EFI or throttle body service, not brake cleaner.
3. Open the throttle plate only as far as needed. On drive-by-wire units, avoid forcing the plate by hand. Use a scan tool to command it open, or unbolt the throttle body and clean it on the bench.
4. Wipe the bore and plate with a lint-free cloth. Don't flood the shaft area with liquid.
5. Let everything dry completely before reconnecting. If the engine idles high afterward, that's often normal. Check the service manual for the idle relearn procedure.

And please don't use brake cleaner to hunt for vacuum leaks. The vapor is flammable, and spraying it near a hot intake or exhaust is how shop fires start. Use a smoke machine or soapy water.

Common Mistakes I See on the Return Bench

Most of the warranty returns I review each quarter follow the same patterns. Headlights returned for flicker that turn out to have corroded terminals. Struts returned with a bent rod that happened during shipping but was never checked before installation. Bushings returned as 'defective' that were actually pressed in wrong and torqued while the suspension was hanging. And throttle bodies blamed for rough idle after someone cleaned them with the wrong solvent and stripped the factory coating.

If a part checks out, install it. If something looks questionable, photograph it and contact the supplier before fitting it. It's far cheaper to send a clean part back than to remove it from the car after 200 miles.

One last honest limitation: this checklist catches parts that are damaged, mislabeled, or about to be installed wrong. It does not predict every long-term failure. No inspection does. If you need absolute certainty for a critical application, ask the supplier for the batch test report or certificate of conformity. For everything else, ten minutes on the bench is usually enough.