Charger stuck at 5 V instead of 20 V


 * PP3V3_G3H missing due to a short circuit on the input to PP3V3_G3H creation circuit
 * Corroded LDO cap for PP3V3_G3H around a CD3215. On boards with 4 ports, on right side of board, check under shielding by SSD under the right CD3215 for hidden corroded cap.
 * PP3V3_G3H missing due to PM_EN_P3V3_G3H missing due to bad ISL9239
 * PP3V3_G3H missing due to CHGR_EN_MVR missing due to bad ISL9240. ISL9240 is not available for purchase. Donor would be required. Watch this troubleshooting video on similar 15" model (A1990) https://www.youtube.com/watch?v=HJ2jyo7pAmE
 * Bad CD3215
 * Bad CD3215 ROM chip (U2890)
 * Test pad corroded and eaten away on the data lines between ROM chip and CD3215
 * Corrupted T2 firmware (when applicable)

If the issue is a bad CD3215, one way to get an idea, is to see which does not boot loop. When you plug the charger in with the USB-C amp-meter, it will turn on for 2-3 seconds, then turn off and turn on again. Whichever port doesn't boot loop usually has an associated CD3215 that is bad. Also, the bad CD3215 will occasionally get hotter than the rest.

T2 firmware can also cause the machine to be stuck at 5v. It is however, important to rule out other possible causes for the issue before re-flashing T2 firmware. Typically machines that have corrupted T2 firmware will be stuck at 5v 0.0 amps and typically will have PPBUS present and PP3v3_S5 missing. PP5V_S5 will often be present. T2 firmware can be re-flashed via Apple Configurator 2, however this will erase data in most cases. Try a "soft" Re-flash first by clicking Advanced options > Revive Device in Apple Configurator 2.