P0C39: DC/DC Converter Temperature Sensor A Range/Performance

P0C39 is the plausibility check of DC/DC converter temperature sensor A: its reading lies within the electrical range but does not fit the converter's operating state or a second sensor. FCA uses it on the 2021 Ram 1500 with the 3.6 litre eTorque mild hybrid, where the code is called temperature sensor 1 performance. Bulletin 08-037-21 updates the HCP software and changes this code from a two-trip to a one-trip DTC, so the MIL can come on after a single fault. Sensor B, sensor 2 at Ram, has the matching code P0C3E. CARB requires rationality checks for such inputs. A drifting sensor or poor thermal contact is typical; outright circuit faults are reported as P0C38, P0C3A or P0C3B instead.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

MIL, after one trip with updated Ram software
Mild hybrid assist or 12 V supply reduced

Most likely causes

Outdated hybrid control software (Ram 1500 eTorque, bulletin 08-037-21)
Sensor A drifting or with poor thermal contact to the power stage
Uneven cooling of the converter making the readings disagree

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Compare the reading with other engine data while varying the engine speed.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0C39 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
39: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0C39?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0C39?

The most common causes are: outdated hybrid control software (Ram 1500 eTorque, bulletin 08-037-21); sensor A drifting or with poor thermal contact to the power stage; uneven cooling of the converter making the readings disagree.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.