A damaged, chafed, or corroded wire in the sensor C signal or return circuit; A loose or contaminated connector at the DC/DC converter or the control module; A failed voltage sensor internal to the DC/DC converter assembly; A faulty DC/DC converter that produces an erratic output the sensor correctly reports as abnormal; A poor ground connection shared by the converter and sensor circuit; A control module with an internal fault in its sensor input circuitry, though this is less common

DTC codes / P0Exx · Hybrid propulsion / P0E99

P0E99DC/DC Converter Voltage Sensor C Circuit

Q: What does code P0E99 mean?

DC/DC Converter Voltage Sensor C Circuit. P0E99 indicates that the powertrain control module has detected an abnormal signal from the voltage sensor circuit associated with the DC/DC converter's phase C output. The DC/DC converter steps high-voltage battery power down to charge the 12-volt system, and the sensor reports the converter's output voltage so the module can regulate it; this code means the module sees a voltage reading outside the expected range or a circuit fault on that sensor's signal path.

P0E99 indicates that the powertrain control module has detected an abnormal signal from the voltage sensor circuit associated with the DC/DC converter's phase C output. The DC/DC converter steps high-voltage battery power down to charge the 12-volt system, and the sensor reports the converter's output voltage so the module can regulate it; this code means the module sees a voltage reading outside the expected range or a circuit fault on that sensor's signal path.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or a dedicated service vehicle warning, often with no other symptoms besides the warning light
A 12-volt battery that slowly discharges or goes flat because the converter is not charging properly
Dimming headlights, flickering interior lights, or weak accessories at idle
Reduced power or a limp-home mode if the vehicle limits high-voltage system operation to protect components
A message on the dash advising that the hybrid or electric system needs service
Intermittent electrical glitches in multiple modules because system voltage is unstable

Common causes, most likely first

A damaged, chafed, or corroded wire in the sensor C signal or return circuit
A loose or contaminated connector at the DC/DC converter or the control module
A failed voltage sensor internal to the DC/DC converter assembly
A faulty DC/DC converter that produces an erratic output the sensor correctly reports as abnormal
A poor ground connection shared by the converter and sensor circuit
A control module with an internal fault in its sensor input circuitry, though this is less common

How to diagnose and fix it

Retrieve all stored codes and freeze-frame data with a scan tool, then clear and road-test to see whether P0E99 returns immediately or only under load
Visually inspect the DC/DC converter connectors and the sensor C wiring for chafing, corrosion, or pushed-back pins, and repair as needed
Measure resistance and voltage drop on the sensor C signal and return wires between the converter and the control module, comparing against the manufacturer's specification
Check the converter's ground strap and mounting points for clean, tight connections, since a bad ground skews the sensor reading
Back-probe the sensor C signal circuit with a multimeter or oscilloscope while the system is active to confirm whether the sensor output is truly out of range
If wiring and grounds are good, substitute a known-good converter or sensor where the design allows, then recheck the code
After repair, clear codes and verify the converter output voltage and sensor reading match the commanded value during a test drive

What the sensor C code really means

This code often sets because of a wiring or connector problem rather than a failed converter, so a thorough circuit check before parts replacement saves significant cost.
A weak or aging 12-volt battery can drag the converter output down and trigger a sensor C voltage code even when the converter itself is healthy.
The sensor C circuit is one of several phase voltage sensors, and a shared ground or reference fault can set multiple related codes at once, so diagnose the common circuit first.
Some vehicles only run the DC/DC converter under specific conditions, so the code may not reappear during a short idle test and requires a loaded road test to confirm the repair.
A converter that is overheating due to a cooling system fault can produce an erratic output that the sensor faithfully reports, making the sensor look guilty when the real problem is thermal.

Can I keep driving with P0E99?

You can usually drive a short distance to a repair shop, but avoid long trips and heavy electrical loads because the 12-volt battery may not be charging correctly. If the battery warning light is on or the vehicle enters limp mode, stop driving and arrange a tow to prevent a no-start or safety system failure.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.