P0A28: Hybrid/EV Battery Power Off Circuit Low

What it means

Voltage on the hybrid battery power-off circuit is low the expected window. Safe HV disconnect signal compromised.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The hybrid or EV battery power-off circuit carries a signal associated with safely disconnecting the high-voltage battery. The control module monitors that circuit and sets P0A28 when its voltage falls below the expected range, which can prevent it from confirming the safe disconnect state.

Common causes

Most likely first.

1. Wire shorted to ground
2. Internal short
3. Connector pins corroded - high contact resistance

Symptoms

• EV/hybrid system warning light on
• Reduced power output or limp mode
• Charging may fail or be slowed
• Reduced electric range

How to diagnose it

1. Record freeze-frame data and check battery power-off circuit live data to see when the low reading occurs.
2. With the vehicle powered down according to the manufacturer's service procedure, inspect the power-off circuit wiring and connectors for damage, corrosion, or moisture.
3. Check for a short to ground in the circuit using the manufacturer's procedure, taking care around high-voltage components.
4. Check connector pin condition and contact quality, since corrosion can disrupt the signal.
5. If the wiring and connections are sound, have the battery control module and circuit tested to distinguish an internal short from a harness fault.

Common fixes

• Clean or repair corroded power-off circuit connector pins.
• Repair wiring shorted to ground.
• Replace damaged circuit wiring or connectors.
• Replace the faulty battery control component if testing confirms an internal short.

Can I keep driving?

Avoid driving if the vehicle has reduced power, enters limp mode, or will not charge normally; the battery may not be safely managed or disconnected. Arrange diagnosis promptly, and do not handle high-voltage wiring.