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DTC codes / P0Exx · Hybrid propulsion / P0E66

P0E66Battery Charger Control Circuit Low

P0E66 indicates that the powertrain control module has detected a low-voltage condition on the battery charger control circuit, which is used to manage charging of the auxiliary battery in hybrid and electric vehicles. The computer expects a certain voltage on the control circuit when commanding the charger, but the signal is lower than expected, indicating a short to ground, an open circuit, or a faulty component.

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

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message
  • Often no symptoms besides the warning light
  • Reduced charging of the auxiliary battery, leading to low battery voltage
  • Electrical accessories may malfunction or dim intermittently
  • Possible no-start condition if the auxiliary battery is depleted
  • In some cases, the vehicle may enter a reduced power mode

Common causes, most likely first

  1. Faulty battery charger control module or integrated power control unit
  2. Damaged wiring harness or connector at the battery charger control circuit
  3. Short to ground in the control circuit wiring
  4. Corroded or loose electrical connections at the charger or battery
  5. Failed auxiliary battery or excessive parasitic draw
  6. Software error in the powertrain control module requiring reprogramming

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in other modules
  2. Inspect the auxiliary battery state of charge and load test it
  3. Visually inspect the battery charger control circuit wiring and connectors for damage or corrosion
  4. Measure resistance and voltage on the control circuit to check for shorts or opens
  5. Test the battery charger control module according to manufacturer procedures
  6. Reprogram the powertrain control module if a software update is available
  7. Replace the faulty component (module, wiring, or battery) as needed and clear the code

Don't overlook the auxiliary battery

  • A weak or failing auxiliary battery can set this code even when the charger control circuit itself is functioning correctly, so always load test the battery first.
  • Corrosion inside a connector that looks fine from the outside is a common cause of low voltage on the control circuit, so wiggle-test and inspect terminals closely.
  • This code can be set by a software glitch in the powertrain control module, and a reprogramming may be required before replacing any hardware.
  • The battery charger control circuit is often part of a larger power management system, so a fault in a related module can trigger this code indirectly.

Can I keep driving with P0E66?

You can usually drive the vehicle with this code, but avoid relying on electrical accessories and do not ignore a low auxiliary battery warning. If the battery is depleted, the vehicle may not start or may enter reduced power mode, so have the charging system checked soon.

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.

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