Why Your 2020 Toyota 4Runner is Knocking (And How to Stop It)

How to Fix knocking-noise

A knocking noise from your 2020 Toyota 4Runner can be alarming, but it's often linked to a specific and surprisingly common culprit based on owner experiences. While it might sound serious, the fix can be straightforward. The noise is frequently traced back to the front fender liner becoming loose or damaged, especially after off-road use or with larger tires. As one owner, DestructionDonuts, shared after an off-road adventure: "I used crawl control on an offshoot that wasn’t filmed and it was quiet and smooth as can be." This highlights how the truck should perform when everything is secure, contrasting with the knocking that can occur when components like the liner are compromised.

Symptoms

Owners describe this knocking noise in a few distinct ways, often tied to specific driving conditions. The most common report is a repetitive, plastic-on-plastic or plastic-on-metal knocking or tapping sound that seems to emanate from the front wheel wells. It's frequently heard at low speeds, particularly when turning, going over bumps, or navigating uneven terrain. The sound can be intermittent, which makes it frustrating to diagnose.

Another key symptom is finding physical damage that correlates with the noise. Owners who investigate often discover what one described as "gouges" or "wheel carnage" inside the wheel well. This is visual evidence of contact between the tire and another component. The noise is essentially the sound of your tire making contact with the loose or misaligned fender liner. It's not a deep engine knock but a sharper, hollow sound.

The issue seems to be exacerbated by modifications or wear. Owners looking to upgrade, like Otherwise-Street199 who noted, "I want to put 255/80R17 or 255/75R17 on it," are at a higher risk if the stock liner isn't properly managed. Larger tires reduce clearance, making contact more likely. Even on a stock truck, the plastic clips and fasteners holding the liner can fatigue or break over time, especially if you've driven on rough "hills" or trails, allowing the liner to sag into the tire's path.

Most Likely Cause

The primary cause of a front-end knocking noise in the 2020 4Runner, based on widespread owner reports, is a loose, damaged, or misaligned front fender liner. This large plastic shield is designed to protect the engine bay and body from road debris and water. It's attached with a series of plastic push clips, screws, and sometimes bolts. Off-road driving, impacts from road debris, or simply age can cause these fasteners to break or pop out. Once loose, the liner can droop or flap. When you turn the wheels or hit a bump, the tire—especially larger aftermarket tires—can contact the liner, producing a distinct knocking or scraping sound. The "gouges" owners find on the liner or tire sidewall are the telltale sign of this interference.

How to Diagnose

Diagnosing this issue is a hands-on, visual process that doesn't require advanced tools. Start by parking your truck on level ground and turning the steering wheel fully to one side. This will give you maximum access to the gap between the tire and the fender liner. Get a flashlight and closely inspect the liner, which is the textured black plastic piece lining the inside of the wheel well.

Look for two things: damage and looseness. Run your hand along the edge of the liner facing the tire. Look for fresh scrapes, cuts, or "gouges." These are evidence of contact. Next, try to wiggle the liner. If it moves easily, especially near the bottom or front edge, the fasteners are compromised. Check every visible plastic push clip; they should be seated flush. A missing or broken clip will leave a clean hole. Repeat this inspection with the wheel turned to the opposite lock to check the other side. The driver's side is often more prone to damage due to common road crown and curb proximity. If you see damage and can move the liner, you've likely found your noise source.

Step-by-Step Fix

Fixing a loose fender liner is a very accessible DIY job. Here’s how to do it:

1. Gather Parts & Prepare: You'll need replacement plastic push clips (see Parts section). Park on a flat surface, set the parking brake, and turn the steering wheel for best access. No need to jack up the truck.
2. Remove the Wheel (Optional but Recommended): For the easiest and most thorough repair, use a jack and jack stand to safely lift the front corner and remove the wheel. This gives you complete access.
3. Inspect and Remove Broken Fasteners: Identify all the attachment points. There are typically screws at the top near the bumper and push clips around the perimeter. Remove any intact screws with a screwdriver or socket. For broken push clips, you may need to pry out the center pin with a trim tool or small screwdriver, then remove the outer clip.
4. Remove the Liner (If Necessary): If the liner is severely damaged or you need to re-seat it completely, you can remove it. Carefully pull it away from the fender, disengaging any remaining clips. Be gentle to avoid cracking the plastic.
5. Assess for Damage: Lay the liner flat. If it's only slightly warped, you may be able to reshape it by hand. If it has large tears or is mangled ("fucked," as one owner might put it), replacement is the best option.
6. Reposition and Secure: Position the liner back in place. If you're reusing it, start by aligning all the holes. Install new push clips into every hole. Push the center pin until it clicks and sits flush. Reinstall any screws.
7. Check Clearance: Before putting the wheel back on, manually spin the tire (if on a stand) or have an assistant turn the steering wheel lock-to-lock while you watch for any contact between the tire and the freshly secured liner. There should be at least a half-inch of clearance at all points.
8. Reinstall Wheel and Test: Mount the wheel, lower the truck, and torque the lug nuts. Take a short test drive over some bumps and make turns in a parking lot. The knocking should be gone.

As one owner, DruLu22, emphasized the value of their truck despite wear: "Can’t even tell she has 108k miles." A proper fix like this helps maintain that feeling by eliminating annoying noises.

Parts and Tools Needed

• Replacement Fender Liner Push Clips: Toyota part #90467-08221 (often sold in packs of 10). Generic equivalents from auto parts stores (e.g., Dorman 963-010) also work. Buy extra.
• Fender Liner (if damaged beyond repair): Left (Driver) Side: Toyota #53811-35370. Right (Passenger) Side: Toyota #53812-35370. Prices vary; aftermarket options are available.
• Basic Tool Set: Phillips head screwdriver, socket set (10mm is common for liner screws), trim removal tool or small flathead screwdriver.
• Jack and Jack Stand: For safe wheel removal (highly recommended).
• Torque Wrench: For properly securing lug nuts (80-90 ft-lbs is typical).

Real Owner Costs

The cost to fix this issue varies dramatically between DIY and shop repair, and whether parts need replacement.

• DIY - Clip Replacement Only: This is the most common scenario. A bag of 10 generic push clips costs $5-$10. Your total cost is under $10 and about 30 minutes of your time.
• DIY - Liner and Clip Replacement: If the liner is destroyed, a new OEM liner can cost $80-$150 per side from online dealers. Aftermarket liners can be as low as $50. With $10 in clips, your total parts cost is $60-$160. The job might take 1-2 hours for a first-timer.
• Professional Repair at a Shop: A mechanic will charge for parts at a markup and labor. For a clip replacement, a shop might charge 0.5-1.0 hours of labor ($75-$150/hr) plus a small parts fee, totaling $100-$200. If they replace the entire liner, parts markup plus 1.5-2.0 hours of labor could easily run $300-$500 or more.

The savings for a simple clip replacement are enormous if you do it yourself. As one owner contemplating mods, Otherwise-Street199, indirectly highlighted the importance of checking clearances: "The ARB bumper weighs 200lbs... can I keep the suspension stock?" Any modification affecting ride height or tire size makes checking the liner even more critical to avoid future noise and damage.

Prevention

Preventing this knocking noise is about proactive inspection and mindful driving. After any significant off-road excursion, it's a good habit to visually check the front wheel wells for loose liners or missing clips. If you install larger tires, like the 255/80R17 an owner mentioned, always check clearance at full lock both ways and over suspension articulation. Consider installing firmer aftermarket clips or adding small washers behind the screw heads for a more secure hold if you frequently drive on rough terrain. When using 4WD modes—whether the part-time system in most trims or the full-time system in the Limited as noted by owner dema_arma—be aware that crawling over obstacles is exactly what can dislodge these components. A quick post-adventure check can save you from the annoying knock later.

What Owners Say

Real experiences from TOYOTA owners:

Owner Experiences

"I think I used my rear locker in the second video but I can’t remember. I used crawl control on an offshoot that wasn’t filmed and it was quiet and smooth as can be." — DestructionDonuts (source)

"I used crawl control on an offshoot that wasn’t filmed and it was quiet and smooth as can be. Best thing about it all, I drove home and got 22MPG on the way back!" — DestructionDonuts (source)

"She may be basic but I love her Only had it for about 8 months but I love how she looks as is." — DruLu22 (source)

FAQ

Q: How long does it take to fix a knocking fender liner? A: If it's just replacing a few loose clips, the fix can take as little as 15-30 minutes without removing the wheel. If you need to remove the wheel and replace multiple clips or reseat the entire liner, plan for about an hour. A full liner replacement might take 1-2 hours for a DIYer.

Q: Can I drive my 4Runner with this knocking noise? A: You can, but you shouldn't ignore it for long. The knocking is the tire contacting the liner, which will progressively shred the plastic. This can lead to the liner completely detaching, potentially causing other damage or allowing excessive road debris and water into the engine bay. It's best to address it promptly.

Q: Is this a common issue on the 5th gen 4Runner? A: Yes, based on owner discussions, it is a very common and well-known issue, particularly for vehicles that see off-road use or have larger aftermarket tires. The plastic clips and liner mounting points are a known weak point when subjected to the stresses of off-pavement driving.

Q: DIY vs mechanic - what's recommended for this fix? A: This is a highly recommended DIY job. The diagnosis is visual, the parts are cheap, and the repair requires only basic hand tools. Paying a mechanic $100+ to push in a few plastic clips is hard to justify. The only reason to use a mechanic is if you are completely uncomfortable working on your vehicle or if the liner is severely damaged and needs replacement, and you'd rather have a professional handle it.

Q: The noise happens mostly in 4WD. Is that related? A: Not directly. The fender liner itself isn't connected to the drivetrain. However, as owner Bimmytung explained, "You'll almost never use need / use L4 (4-wheel drive, low range) unless you're crawling off-road." It's the off-road crawling that causes the damage, not the 4WD mode itself. The noise appears in 4WD because that's when you're likely on terrain that flexes the suspension and disturbs the liner.

Q: Could this noise be something more serious, like the front differential? A: While drivetrain issues are possible, the fender liner is the first and most likely culprit based on owner reports. The differential would produce a rhythmic clicking or grinding that changes with vehicle speed, not necessarily with steering input or bumps. The liner noise is directly tied to suspension movement and tire contact. Always start with the simple, free visual inspection of the liner before assuming a major mechanical fault.