Hello!
Does anyone know what this white component is, and what its role is in the SIM800L module circuit?
Thanks in advance!

 

That has the appearance of a SMT LED.?

 

That has the appearance of a SMT LED.?

Thank you, it's not an LED
The component is slightly thicker than the nearby 100 nF ceramic capacitors.
It is connected between GND and one QFN pin of the SIM800L (not VBAT — VBAT is connected to a tantalum capacitor which I already checked).
Color: white/cream, rectangular package, looks similar to a ceramic capacitor but thicker.
There is no marking on top.
I’d like to know if this part is a capacitor or ferrite or something else?

 

it is either capacitor or upside down resistor or possibly a fuse. LED is shown on the corner (top right). resistor mounted proper way is next to it.

 

Thanks,
After tracing the board more carefully, I discovered the following:
The small MLCC is connected between VCC of the SIM card holder and GND. So it’s just a local decoupling capacitor for the SIM supply.
The white/thicker SMD part is connected between the SIM I/O line and GND. This makes sense as an ESD protection device (TVS), or possibly part of the recommended SIM interface filtering (TVS + R + C).
I’ll add a photo showing these connections for clarity. My next step is to desolder both parts and measure them to confirm (capacitance for the MLCC, diode behavior for the TVS). Once I have the results, I’ll post them here as the final update.

 

SOLVED
Thanks again to everyone for the help. I desoldered the two parts and measured them:
The small brown MLCC is 1 µF, used as a decoupling capacitor on the SIM VCC pin.
The thicker white SMD is also a capacitor (~22 pF), not a TVS. It’s part of the SIM interface RC filter (22 Ω + 22 pF to GND) recommended in the SIM800L datasheet.
On the cheap red SIM800L board, the 22 Ω series resistors are omitted (probably to save cost), so only the capacitors are left. On the bigger module version, both the resistors and capacitors are present, exactly as shown in the reference design.
So in short:
1 µF MLCC = SIM VCC decoupling
22 pF MLCC = SIM I/O line filtering

 

Hello!
Does anyone know what this white component is, and what its role is in the SIM800L module circuit?
Thanks in advance!

It looks like an SMD resettable fuse (polyfuse / PPTC fuse) to me. https://fuse-china.en.made-in-china...able-Fuse-2410-6125-PPTC-Resettable-Fuse.html