2015 Leaf - DC-DC Converter Failure Diagnosis - Can you confirm?

[Benity44]

My 2015 Leaf (24kWh, 66,848 miles) recently went into turtle mode and stopped recognizing charging attempts. The car still drives, though speed is restricted, and I'm getting multiple CAN communication errors along with various system warnings.

Initially, I had multiple error codes including CAN communication errors, EV/HEV system errors, battery voltage abnormal warnings, and a key fob registration error. I replaced the 12V battery, but the voltage behavior strongly suggests a DC-DC converter failure. With the new battery, I'm seeing 12.25V with the car off, which drops to 12.09V with the car on (should rise to 13.5-14V), and further falls to 11.96V with lights on. The voltage continues declining under load instead of maintaining charge.

LeafSpy readings show the main battery appears healthy with 79.3% SOC at 388.2V, consistent cell voltages around 4.04mV, and normal battery temperature around 67°F. However, the 12V system shows 12.08V, confirming the undervoltage condition. I've tested all fuses (good) and checked for visible wiring damage or charging port issues (none found).

My theory is that a failed DC-DC converter explains all symptoms since it can't maintain proper 12V system voltage, which causes the CAN communication failures, prevents the charging system from initializing, and triggers protective modes like turtle mode. The main battery and other systems appear healthy, suggesting the issue is isolated to the DC-DC converter.

Can anyone confirm if this diagnosis aligns with their experience? Also looking for recommendations on DC-DC converter replacement options. For reference, the car has seen 15 QCs and 2515 L1/L2s over its lifetime.

One more observation: While driving the car prior to replacing the battery, it would slow down DRAMATICALLY if I turned on a blinker or the headlights. After replacing the original 12V battery (which was at just over 11V), the car showed significantly better acceleration, though still limited by turtle mode.

Here are my DTCs:

Ok None ---> ABS
Ok None ---> AIR BAG
>B26FC-00 09 BCM Keyfob Miss Registration SEC-90
Ok None ---> BRAKE
Ok None ---> EPS
>P3196-00 0B EV/HEV CAN Error EVC-274
>U1000-00 0B EV/HEV CAN Comm Circuit
Ok None ---> HVAC
U1000-00 4E HV BATTERY CAN Comm Circuit
P3196-00 4E HV BATTERY CAN Error EVB-99
Ok None ---> IPDM E/R
Ok None ---> METER
Ok None ---> MOTOR CONTROL
Ok None ---> SHIFT
Ok None ---> VSP

Thanks folks!

 

[cornbinder89]

Have you tried clearing the codes and seeing if they return? If they come back, I would say PDM, but clear codes 1st.

 

[Benity44]

Yep- they come back immediately. Thank you for your input!

 

[nlspace]

You need to fully charge your new 12V battery, 12.25 OCV is not fully charged (expecting 12.8 or more).

With the new battery, I'm seeing 12.25V with the car off

Once you rule out the low system voltage then you can do troubleshooting if any codes remain, many times they clear with proper system voltage, e.g CAN Buss errors

There is a 30A fuse inside the PDM on the HV + copper buss bar. If it is blown then the car won't charge nor will the DCDC get power to charge the 12V battery. Search for a thread about adding chademo to the PDM for pictures.