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I have observed that the daytime running light on the passenger side appears to be nonfunctional, yet the left turn signal operates correctly and the primary headlight beam is also functioning. The daytime running lights are nonfunctional; specifically, the elongated strip at the top and the three LED bulbs do not operate. However, upon exiting the vehicle and attempting to activate the car with the key fob, the top strip appears to illuminate. Any guidance would be greatly valued. Apologies for not mentioning earlier that I possess a 2019/2020 Toyota C-HR Hybrid with a 1.8-liter Excel engine.

Examine the left front wheel arch and bumper region for any indications of damage initially.

The left headlight serves as the entry point for thieves on specific C-HR models.

I apologise for neglecting to state that I have inspected the left side and found no evidence of damage to the left wheel arch.

You have arrived at the correct location! The complete LED headlight system on the Toyota C-HR Excel (2019/2020) is an intelligent, multifunctional unit.
The conduct you are outlining—where the LED strip operates during the "welcome/unlock" sequence but malfunctions when the engine is ignited—is indeed a recognised diagnostic indicator. It indicates that the LED chips within the light are entirely functional, thus negating the necessity for a costly complete headlight replacement!

What is the source of this?

The headlight assembly of the C-HR Excel employs various voltage and signal pathways for distinct functions.
Greetings/Activate Light Mode: When you activate or deactivate the vehicle using the key fob, the Body Control Module transmits a low-voltage "parking/location light" signal to the light strip. This mode is functioning properly.
Daytime Running Light (DRL) Mode: Upon shifting the vehicle to "READY" mode and disengaging from Park, the lighting control system elevates the brightness of the LED strip through a specific DRL signal wire and LED driver module.
Since your light engages for the welcome illumination, the indicator, and the primary beam, the problem is confined to the DRL switching mechanism.

Essential Aspects to Verify Initially

1. The Electronic Parking Brake / Gearbox Condition
In Toyota hybrids, the daytime running lights are configured to stay OFF until the vehicle is ignited and shifted out of Park (or until the electronic parking brake is disengaged).
Ensure that you are evaluating the DRLs while the vehicle is in "READY" mode, either in Drive or Neutral (with the handbrake disengaged), instead of merely having the ignition activated in Park.
Examine the settings for infotainment lighting.
The system logic may have malfunctioned within the configurations:
Access the central touchscreen, then navigate to Setup $\rightarrow$ Vehicle $\rightarrow$ Vehicle Customisation $\rightarrow$ Lights.
Verify whether the Daytime Running Lights feature is activated. Deactivate it and then reactivate it to refresh the configuration.
3. Unsecured Wiring Harness / Multi-Pin Connector
Since the indicator and primary beam are operational, the principal ground wire remains undamaged. Nonetheless, the particular terminal pin within the multi-way headlight connector that transmits the DRL-high signal may have experienced minor oxidation or a loose connection.
Accessing the area behind the passenger headlight assembly within the engine compartment, one will observe a substantial, multi-pin electrical connector affixed to the rear of the headlight casing.
Depress the locking tab, detach the plug, inspect for any moisture or debris, and securely reinsert it until it audibly clicks.
4. The LED Driver Component / Fuse
The Excel LED headlights possess an integrated or affixed sub-driver ECU that amplifies the voltage for optimal DRL performance. Should the connection or internal switching circuit of that sub-module malfunction, it will permit the dim welcome light to activate, yet will not initiate the bright DRL mode.
Summary Suggestion
Given that your vehicle is a 2019/2020 Excel, provided you have consistently adhered to annual servicing with Toyota, your automobile ought to be safeguarded by the Toyota Relax warranty (which lasts for up to 10 years or 100,000 miles).
Since the LEDs illuminate upon unlocking, do not allow a garage to assert that a brand new headlight assembly costing over £1,000 is necessary. Schedule an appointment with a Toyota dealership and inform them: "The passenger daytime running light malfunctions in READY mode, yet the LED strip operates during the welcome/key fob unlock sequence. They are able to examine the signal pin or substitute the headlamp driver control module under warranty.

Thank you for your response; I will review your suggestions tomorrow and provide you with an update concerning the infotainment screen. However, I did disconnect the grey plug in the engine bay that connects to the headlight, yet it remains nonfunctional. Additionally, I should note that my specific model has three LED bulbs for the daytime running lights, which, along with the strip, also appear to be inoperative. I will heed your advice, but regrettably, I have not been servicing my vehicle at Toyota since I purchased it second-hand, and it has surpassed 100,000 miles, currently totalling 130,000 miles, to be fair.

I appreciate the update; the additional details regarding your vehicle's trim level and mileage provide much greater clarity.
Given that your 2019/2020 Excel model is equipped with the enhanced Full LED Headlights (featuring the upper strip and the three lower LED array) and has exceeded 100,000 miles, here is the probable issue and a cost-effective solution without incurring main dealer expenses.

1. Initially inspect the Dedicated DRL Fuse.

In the engine compartment fuse box, Toyota provides a specific 10A DRL fuse for the lighting circuit.
The significance of this issue: The welcome/unlock feature operates through a low-voltage parking light circuit, powered by the interior TAIL or PANEL fuse, hence the illumination activates upon unlocking the vehicle. Nevertheless, upon initiating the hybrid system, it transitions to the high-capacity DRL 10A fuse.
Action: Remove the cover of the fuse box located beneath the hood and examine the diagram affixed to the interior lid for the DRL (10A). Should that fuse be defective, substituting it for under £1 may rectify the problem immediately.
2. The DRL Control Module (The Most Frequent Offender at 130,000 Miles)

The complete LED Excel headlights feature a top LED strip and three lower DRL LEDs, both energised by a compact bolt-on LED Driver Control Module affixed to the rear/bottom of the headlight housing.
After exceeding 130,000 miles of thermal cycles and road oscillations, the internal switching transistor within this compact driver module may fail.
Upon failure, it ceases to supply power to the luminous DRL mode (deactivating both the three-bulb array and the strip in daytime mode), yet permits the low-voltage welcome light signal to continue transmitting.
3. Financial Alternatives for Repairing It (Steering Clear of Primary Dealer Expenses)

Given that a brand-new comprehensive Excel LED headlight assembly from Toyota is priced at over £1,000, you have two significantly more economical alternatives:
Substitute solely the LED Daytime Running Light Driver Module (£30 – £60):
There is no necessity to substitute the complete headlight assembly. Independent automotive electricians or specialised lighting vendors offer replacement plug-and-play DRL control modules tailored for the C-HR Excel headlight. Detaching the antiquated module from the rear of the headlight assembly and connecting a new module frequently rejuvenates both the strip and three LEDs immediately.
Purchase a pre-owned OEM headlight assembly (£200 – £350):
If the internal light board is compromised, explore platforms such as eBay or nearby auto dismantlers for a pre-owned authentic Toyota C-HR Excel Left/Passenger LED Headlight. They are easy to exchange at a nearby independent garage.
Examine the infotainment settings and the 10A engine bay fuse tomorrow, and determine if substituting solely the bolt-on DRL module is the optimal course of action!

I examined my infotainment system today and found no options for the vehicle's DRL light. Additionally, my research indicates that the 2018 Toyota C-HR Excel lacks a specific 10A DRL fuse, suggesting that the issue may lie with either the control module or the headlight unit, both of which are quite expensive at the dealership. Consequently, I am considering purchasing from eBay or seeking a Toyota car breaker, as dealership prices are exorbitant. Thank you for your assistance; I greatly appreciate it.

I trust you will discover an economical solution to the issue!

It occurred to me. Additionally on the side of the passenger. Precisely the identical symptom as what you are delineating.
I was required to substitute the complete component. It is sealed and cannot be disassembled to replace solely the white DLR.

Naturally, it is far from inexpensive!

I explored the secondary market, yet the Orange C-HR exists in its own "realm," preventing me from locating the precise component.

Hello, what actions did you ultimately take to resolve the problem? Is the component new or pre-owned?