Powertrain, generic

P0E99 DC/DC Converter Voltage Sensor C Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

With P0E99 the controller finds the voltage sensor C reading of a DC/DC converter pinned near its upper limit. That points to the signal touching a battery feed or reference supply, or to a broken sensor ground that lets the input float up, rather than to a real converter overvoltage. No manufacturer documents P0E99 publicly. For channels A and B GM's 2025 engine tables (25OBDG03A) use more than 28 V as the limit for a 12 V converter, far beyond any genuine output, and confirm P0E34 or P0E39 after 320 of 400 failed samples as Type B. CARB demands such out-of-range checks. Comparing sensor C with the other channels and the battery voltage quickly separates a wiring fault from a converter problem; low readings are P0E98.

Likely causes

Sensor C signal shorted to battery voltage or reference supply
Open sensor ground letting the signal float high
Actual overvoltage from a faulty converter regulation

Symptoms

  • MIL and charging or 12 V warning possible
  • Converter limits or stops its output
  • Start-stop function unavailable

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

dcdc voltage sensor cwiring harnessdcdc converter

Related codes

P0E98P0E96P0E97P0E9AP0E34P0E39

References: law.cornell.edu, gsi.ext.gm.com.