P2E91: Battery Charger B Internal Power Supply Performance

What it means

The internal low-voltage power supply of battery charger B does not maintain the expected output. Internal regulator drift or overload.

At a glance

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

How it works

Battery charger B has its own internal low-voltage supply for its control electronics. The vehicle monitors that supply and sets this code when charger B cannot maintain its expected performance, which can interfere with charging.

Common causes

Most likely first.

1. Internal regulator drifted
2. Internal load increased

Symptoms

• Charge status indicator shows fault
• Charging may not start or interrupts
• Slower-than-expected charge rate

How to diagnose it

1. Read charging-system codes and freeze-frame data, and note whether the fault occurs when charger B is asked to operate.
2. Check scan-tool charging status for repeatable evidence that charger B is affected rather than charger A.
3. Inspect charger B's accessible connectors and wiring for corrosion, loose terminals, damage, or overheating.
4. Verify the external low-voltage feed and grounds to charger B against the manufacturer's specification.
5. If its external circuits are sound, test charger B's internal supply using the manufacturer's diagnostic procedure.

Common fixes

• Clean and secure charger B's accessible power, ground, and control connectors.
• Repair damaged external supply or ground wiring to charger B.
• Repair or replace charger B if its internal supply fails testing after external circuits are verified.

Can I keep driving?

Charging can fail, interrupt, or run slower than expected if charger B's internal supply is unstable. Keep an eye on available charge and do not rely on charger B until the fault is resolved.