P0BC9: Hybrid/EV Battery Pack Cooling Fan 1 Sense Circuit Low

P0BC9 means the speed feedback of battery cooling fan 1 is implausibly low while the fan is running. GM evaluates the feedback as a frequency: in its 2016 and 2018 hybrid tables the code counts a failure when the frequency stays below 8 Hz with the fan enabled at 11 to 89 % duty for more than 8 s and system voltage above 10.2 V; 16 failures in 20 samples at 250 ms set it as Type B, two trips. A frequency near zero comes either from a fan that is not turning or from a feedback line shorted to ground or interrupted. The high case is P0BCA, a speed that is merely too far from the target is P0BC8, and drive circuit faults are P0A81 to P0A85. Expect power limits when the pack warms up.

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 on after two trips
No airflow from the battery cooling fan
Reduced power when the battery gets warm

Most likely causes

Fan seized, blocked or without power
Feedback wire shorted to ground or interrupted
Failed speed sensor inside the fan unit

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
With the connector unplugged, check whether the signal wire is making contact with ground.
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 P0BC9 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
B: Subsystem depends on the code range
C9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0BC9?

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 P0BC9?

The most common causes are: fan seized, blocked or without power; feedback wire shorted to ground or interrupted; failed speed sensor inside the fan unit.

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.