P0DB9: Hybrid/EV Battery Cell Balancing Circuit D Stuck On

A stuck-on circuit D (P0DB9) drains group D continuously. The usual check is simple: does the switch state reported back equal the state the controller asked for? GM applies this on the eAssist battery for a related code, sampling every 200 ms and logging a Type B fault after 7 mismatches in 10. Here the reported state stays on while the command says off. Besides the voltage loss, the bleed resistor keeps warming its part of the module, which can upset temperature readings nearby. On Ford hybrids the code is real: the 2019 OBD summary checks circuit D for 0.1 s at each start, before the high voltage contactors close, against a 75 mV deviation of any of its six cells from the average. The broken-circuit case is P0DB8, the inactive case P0DBA.

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 with battery warning
Group D cells and their local temperature deviating
Loss of charge while parked

Most likely causes

Balancing transistor of circuit D shorted
Status feedback of the module wrong, switch actually fine
Drive output of the monitoring chip stuck on

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
Use the scanner to command the movement and compare the actual position with the requested one.
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 P0DB9 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
D: Subsystem depends on the code range
B9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0DB9?

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 P0DB9?

The most common causes are: balancing transistor of circuit D shorted; status feedback of the module wrong, switch actually fine; drive output of the monitoring chip stuck on.

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.