01 Who is at Fault When a Car Turns Right and a Bike Goes Stra… • 02 Extend Your Car's Lifespan to 300000 Miles with These Power… • 03 The Ultimate Guide to Inspect a Used Car Before Buying • 04 iStop: The Revolutionary Brake-Activated Auto Stop-Start Sy… • 05 The World's Biggest and Strongest Ship Engines: A Comprehen… • 06 Troubleshooting Coolant Mixing with Oil in Your Engine: Cau… • 07 This Is Why Your Car’s Differential Fluid Needs Changing • 08 You Might Stall On The Highway If You Keep Ignoring That Ra… • 09 8 Factors That Contribute to High Fuel Consumption • 10 P0024 B camshaft position - timing over advanced or system … •

DTC codes / P0Dxx · Hybrid propulsion / P0D21

P0D21Battery Charger A Output Voltage Too Low

P0D21 indicates that the vehicle's battery charger system, typically the onboard charger in a plug-in hybrid or electric vehicle, has reported an output voltage that is below the expected threshold during charging. The control module monitors the charger's output and sets this code when the voltage fails to reach the commanded level within a specified time, often due to a fault in the charger, high-voltage wiring, or the battery pack itself.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Charging indicator may show a fault or stop charging prematurely
  • The vehicle may not accept a charge or charging time is significantly longer
  • A warning light or message on the dash indicating a charging system problem
  • Reduced electric driving range or the vehicle may default to gasoline engine operation
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty onboard battery charger module
  2. High-voltage cable or connector damage, corrosion, or loose connection
  3. Low or failing 12-volt auxiliary battery affecting charger control electronics
  4. Software glitch in the charger control module requiring reprogramming
  5. High-voltage battery pack issue causing the charger to reduce output
  6. Blown fuse or relay in the charger power circuit
  7. Ground connection problem for the charger or high-voltage system

How to diagnose and fix it

  1. Perform a visual inspection of the charging port, high-voltage cables, and connectors for damage or corrosion
  2. Check the 12-volt battery state of charge and condition, as low voltage can cause false charger codes
  3. Use a scan tool to read all stored codes and freeze-frame data, then clear the code and test-drive to see if it returns
  4. Measure the charger's output voltage with a multimeter at the high-voltage battery terminals during charging, following manufacturer safety procedures
  5. Check fuses and relays related to the charger circuit and replace any that are faulty
  6. Inspect and test the high-voltage wiring for continuity and insulation resistance, repairing or replacing as needed
  7. If all else checks out, reprogram or replace the onboard charger module according to the manufacturer's diagnostic flow

Charger voltage codes often misdiagnosed

  • A weak 12-volt battery can cause the charger control module to misreport output voltage, so always load-test the auxiliary battery before condemning the charger.
  • Intermittent P0D21 often stems from a poor ground connection at the charger or high-voltage junction box, which is easily overlooked during visual inspection.
  • Some vehicles set this code when the charging station's voltage is unstable, so verify the external charging equipment before diagnosing the vehicle.
  • The code can be stored by a software bug in the charger module; checking for and applying the latest software update is a valid first step on affected models.
  • High-voltage battery degradation may cause the charger to reduce output to protect the pack, setting this code without any charger fault.

Can I keep driving with P0D21?

If the vehicle is a plug-in hybrid, it can often be driven on the gasoline engine, but avoid long trips relying on electric power. For a pure electric vehicle, driving range may be severely limited, so plan to have the fault diagnosed promptly and avoid depending on the vehicle for essential journeys.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage