P0C4D: Hybrid/EV Battery Pack Coolant Pump A Supply Voltage Circuit High

P0C4D is the counterpart to P0C4C: the voltage measured on the supply of battery coolant pump A is higher than the controller allows. That can come from a feed wire shorted to another, more highly loaded circuit, from a relay that stays closed when the pump should be off, or from an overall excessive on-board voltage, for example a faulty DC/DC converter. No manufacturer documents P0C4D publicly. Ford's bulletins for the 2020 Escape, Explorer and Aviator hybrids name the sibling P0C4B for the open supply, and Bentley describes the feed of the same pump with fuse and relay for 2025–2026 hybrids. CARB requires the electrical components of battery thermal management to be monitored. If several modules log overvoltage at once, the 12 V supply is the more likely culprit than the pump circuit.

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 or hybrid or EV warning
Coolant pump running although the system is switched off

Most likely causes

Supply wire shorted to another voltage-carrying circuit
Pump relay sticking closed
Excessive 12 V system voltage from a faulty DC/DC converter

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
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P0C4D means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
4D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0C4D?

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 P0C4D?

The most common causes are: supply wire shorted to another voltage-carrying circuit; pump relay sticking closed; excessive 12 V system voltage from a faulty DC/DC converter.

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.