P0D20: Battery Charger A Output Voltage Performance

P0D20 concerns the on-board charger in its constant-voltage phase, typically near the end of a charge, when it should hold its high-voltage output at a set value. The code means the measured output voltage strays too far from that target. GM's 2011 to 2013 Chevrolet Volt evaluates this in the HPC2/VICM: a deviation of 15 % or more in constant-voltage mode, counted at 100 ms with system voltage above 9 V (2011) or 10.2 V (2012), sets the code after 30 failures in 50 samples, One Trip Type A, so the MIL comes on at once. Later GM tables no longer list it. CARB requires charger faults that stop or slow charging to be detected. Causes lie mostly inside the charger or its voltage sensing. Charging stops or ends early; driving is unaffected. Too low a voltage is P0D21.

Symptoms

• Charging stops early or the battery does not reach its target level
• MIL and charging system message

Most likely causes

• Fault in the charger's power stage or voltage control
• Inaccurate output voltage measurement
• Charge control software in the hybrid control module

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Compare the reading with other engine data while varying the engine speed.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

What each character of P0D20 means

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

Frequently asked questions

Can I keep driving with code P0D20?

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 P0D20?

The most common causes are: fault in the charger's power stage or voltage control; inaccurate output voltage measurement; charge control software in the hybrid control module.

Related codes

• P0D21Battery Charger A Output Voltage Too Low
• P0D85Battery Charging Output Voltage Too High
• P0D22Battery Charger A Output Current Performance
• P2E3ABattery Charger B Output Voltage Performance

Sources

• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• gsi.ext.gm.com: 12OBDG01A HYBRID Diagnostics
• law.cornell.edu: 13 CCR 1968.2

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.