# 2021 Kia Seltos Engine Making Knocking Sound: Diagnosis & Fixes > ClearTheCode — Is your 2021 Kia Seltos engine making a knocking sound, especially during acceleration? Learn common causes, how to diagnose, and effective fixes to restore engine health. Source: https://clearthecode.com/articles/engine-knocking-noise-kia-seltos-2021 Author: ClearTheCode # 2021 Kia Seltos Engine Making Knocking Sound Experiencing a distinct knocking or tapping sound from your 2021 Kia Seltos engine, particularly when you accelerate, can be a concerning issue for any owner. This article dives into the common reasons your 2021 Kia Seltos engine might be making a knocking sound, how to accurately diagnose the problem, and the potential solutions to get your vehicle running smoothly again. ## What drivers notice on this 2021 Kia Seltos Drivers of the 2021 Kia Seltos often report a metallic, rhythmic knocking or tapping noise emanating from the engine bay. This sound is typically most noticeable under specific conditions: - **During acceleration:** The knocking may become louder or more pronounced as you press the accelerator, especially when the engine is under load. - **Cold starts:** The noise might be more apparent immediately after starting the engine, potentially lessening as the engine warms up. - **Varying with RPM:** The frequency of the knock often increases or decreases with engine revolutions per minute (RPM). - **Loss of power:** In some cases, the knocking sound can be accompanied by a noticeable reduction in engine power or sluggish performance. ## At a glance: difficulty, repair cost, and diagnostic workflow - **Difficulty Rating:** 6/10 — Moderate - **Common Symptoms:** Distinct metallic knocking or tapping sound: This is the primary indicator, often described as a 'rod knock' or 'piston ; Noise often more prominent during acceleration or under load: The engine's stress level can exacerbate the sound.; Sound may change with engine RPM: A consistent rhythm tied to engine speed is a key diagnostic clue.; Reduced engine power or sluggish acceleration: The engine might struggle to produce its usual output. - **Estimated Repair Cost:** $100–$900 (parts + typical shop labor) - **OEM Tooling Required:** Standard OBD-II scanner and hand tools **Diagnostic workflow:** 1. Confirm the symptom on your 2021 Kia SELTOS. 2. Scan for stored or pending codes with an OBD-II tool. 3. Inspect the most common causes in this guide (visual checks first). 4. Run verification tests before replacing parts. 5. Repair, clear codes, and verify on a test drive. Browse the [model repair hub](/vehicles/kia/seltos) and [make hub](/vehicles/kia) for related guides. ## Symptoms and warning signs Beyond the primary knocking noise, pay attention to these other symptoms that might accompany the sound in your 2021 Kia Seltos: - **Distinct metallic knocking or tapping sound:** This is the primary indicator, often described as a 'rod knock' or 'piston slap' depending on its character. - **Noise often more prominent during acceleration or under load:** The engine's stress level can exacerbate the sound. - **Sound may change with engine RPM:** A consistent rhythm tied to engine speed is a key diagnostic clue. - **Reduced engine power or sluggish acceleration:** The engine might struggle to produce its usual output. - **Illuminated Check Engine Light (CEL):** Various engine issues, including misfires or timing problems, can trigger the CEL. - **Rough idling or vibrations:** The engine may not run smoothly, causing noticeable vibrations. - **Increased oil consumption:** If the knocking is related to internal wear, you might notice your Seltos consuming more oil than usual. - **Abnormal exhaust smoke:** Depending on the cause, you might see blue smoke (oil burning) or black smoke (rich fuel mixture). ## How to verify and confirm the issue Confirming the source of an engine knocking sound in your 2021 Kia Seltos requires a systematic approach: - **Listen carefully with a mechanic's stethoscope:** This tool allows you to pinpoint the exact location of the sound within the engine bay, helping differentiate between top-end (valvetrain) and bottom-end (crankshaft, rods) noises. - **Check engine oil level and quality:** Low oil pressure or contaminated oil can lead to knocking. Ensure the oil level is correct and inspect its color and consistency. If it's very dark, gritty, or smells burnt, an oil change is overdue. - **Scan for Diagnostic Trouble Codes (DTCs):** Use an [OBD-II scanner](https://clearthecode.com/codes) to check for any stored or pending codes. While no specific code directly indicates a knock, codes related to misfires (P03XX), variable valve timing (P0011, P0014), or catalytic converter efficiency (P0420) can point to related issues. - **Review live data with a scan tool:** Look at parameters like fuel trims, misfire counts per cylinder, oxygen sensor readings, and VVT/VCT (Variable Valve Timing/Camshaft Timing) angles. Abnormal readings can indicate fuel delivery, ignition, or timing problems. - **Visual inspection:** Look for obvious issues like loose belts, damaged pulleys, exhaust leaks (which can sound like a knock), or vacuum leaks. - **Fuel quality check:** If you suspect poor fuel, try running a tank of higher-octane fuel to see if the knocking subsides. - **Consider a compression test or leak-down test:** If internal engine damage is suspected, these tests can reveal issues with pistons, rings, or valves. ## Common causes (most likely first) Several factors can cause a 2021 Kia Seltos engine to develop a knocking sound. Here are the most common culprits: - **Low or dirty engine oil:** Insufficient lubrication is a primary cause of metallic knocking as moving parts make contact. Dirty oil can also lose its lubricating properties. - **Poor fuel quality (low octane):** Using fuel with an octane rating lower than recommended can lead to pre-ignition or ### Related guides on this vehicle - [2020 Kia Sorento Engine Knocking: Diagnosis & Fixes](/articles/engine-knocking-noise-kia-sorento-2020) - [2019 Kia Forte Engine Knocking Sound: Diagnosis & Fixes](/articles/engine-knocking-noise-kia-forte-2019) - [2018 Kia Sorento Engine Knocking: Diagnosis & Repair Guide](/articles/engine-knocking-noise-kia-sorento-2018) ## Related pages - All repair guides - [Browse vehicles](/vehicles) - [Browse OBD-II codes](/codes) - [Kia vehicle hub](/vehicles/kia) - [Seltos model hub](/vehicles/kia/seltos) --- This guide is not a substitute for OEM service procedures; use a qualified technician for safety-critical repairs. ## Frequently asked questions ### How urgent is this problem? If symptoms are worsening or safety systems are affected, diagnose soon; minor issues can often wait for a scheduled service visit. ### Can I drive with this issue? Short trips may be acceptable for some faults, but stop driving if you notice overheating, loss of braking, steering problems, or strong fuel smells. ### Do I need a dealer scan tool? A basic OBD-II scanner helps confirm codes; some steps still need visual checks and meter tests described above.