P0A29: Hybrid/EV Battery Power Off Circuit High

What it means

Voltage on the hybrid battery power-off circuit is high 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 sets P0A29 when circuit voltage rises above its expected range, so it may not recognize the intended disconnect signal.

Common causes

Most likely first.

1. Wire shorted to B+
2. Pull-down resistor open
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 review power-off circuit live data to confirm when the high reading appears.
2. With the vehicle powered down according to the manufacturer's service procedure, inspect the circuit harness for damage or contact with a B+ source.
3. Inspect connectors for corrosion, loose pins, or poor contact that could interrupt the intended signal path.
4. Test the circuit for a short to B+ using the manufacturer's procedure and suitable high-voltage safety precautions.
5. If the harness and connectors pass inspection, have the pull-down resistor and battery control circuitry tested against the manufacturer's specification.

Common fixes

• Clean or repair corroded power-off circuit connector pins.
• Repair wiring shorted to B+.
• Replace damaged circuit wiring or connectors.
• Replace the failed pull-down resistor or control component if testing confirms it is open.

Can I keep driving?

Avoid driving if the vehicle has reduced power, enters limp mode, or charging is disrupted, because high-voltage battery control may be compromised. Arrange diagnosis promptly and keep clear of high-voltage wiring.