jeep charger blinking red and yellow

The most common cause of the Jeep charger’s red and yellow lights flashing simultaneously is abnormal contact/communication between the charger and the power source or battery (poor plug contact or BMS preventing charging).

Following the order from easiest to hardest to check, here are 8 troubleshooting steps (checklist format), each including: Symptom → Possible Cause → Solution → Precautions.

1) Check the AC power supply and socket.

• Symptom: The charger indicator light flashes, and charging either stops or works intermittently.
• Possible causes: The wall socket is not powered, the circuit breaker has tripped, or the power supply voltage is unstable.
• Solutions: Replace with a confirmed powered outlet; check and reset the circuit breaker or residual current device in the distribution box; avoid using extension cords or aging outlets as much as possible.
• Precautions: Ensure the charger is turned off before connecting to the power source; do not use a damaged power cord or a damp socket.

2) Check the connection of the charger power cord and AC plug.

• Phenomenon: The light flashes or turns on and off intermittently after the power is plugged in, and its status changes when the cable is moved slightly.
• Possible causes: poor plug contact, internal cable breakage, or oxidation/corrosion of the plug terminals.
• Solution: After disconnecting the power, unplug the power cord and check the cleanliness of the plug terminals. If necessary, clean them with a contact cleaner and reinsert them tightly. Replace the damaged power cord.
• Precautions: Always disconnect the mains power before cleaning or replacing; avoid washing the contact surface with water.

3) Check the connection between the charging port and the battery (DC side plug/cable).

• Symptom: The charger light flashes but the current is very small or zero, or the fault disappears upon contact.
• Possible causes: Loose, oxidized, or poorly contacted charging port, plug, or battery terminals.
• Solution: Disconnect all connections, clean and check the pins/sockets for deformation, tighten the connectors and apply an appropriate amount of anti-oxidant (for lead-acid or nickel-cadmium batteries).
• Precautions: Wear insulated gloves during operation to avoid short circuits; ensure there are no loose parts after cleaning before turning on the power.

4) Check the fuses and vehicle circuit breaker (FUSE/CB).

• Symptom: The charger light flashes or indicates an error code, and charging is interrupted.
• Possible cause: The fuse in the vehicle or charger has blown, and the protection circuit has been activated.
• Solution: Check the fuses/circuit breakers on the vehicle and charger, and replace blown fuses or reset circuit breakers according to specifications.
• Precautions: When replacing a fuse, you must use one with the same rating and type; do not use copper wire or similar materials as a substitute, as this may cause further damage or fire.

5) Verify voltage matching and specifications (charger vs. battery pack)

• Symptom: The charger is connected but does not start charging normally, or the charging screen flickers abnormally.
• Possible causes: The charger’s output voltage/current does not match the battery’s rated voltage (e.g., a 36V charger connected to a 48V battery), or the charger is for a different battery chemistry.
• Solution: Confirm that the charger nameplate parameters are consistent with the battery’s nominal voltage and chemical type (lead-acid, LiFePO4, etc.); if necessary, replace with a matching charger.
• Precautions: Do not use an incompatible charger for extended periods; incorrect voltage or charging curves can damage the battery and pose safety risks.

6) Check for BMS (Battery Management System) protection or communication faults.

• Symptoms: The charger light flashes and displays “Waiting/Error,” and the vehicle or battery display shows a BMS alarm or indicates that charging is not allowed.
• Possible causes: The BMS detects individual cell voltage imbalance, over-discharge/over-charge, abnormal temperature, or communication interruption, and actively cuts off charging.
• Solution: Read the BMS/vehicle fault codes (instrument panel or dedicated diagnostic tool), and troubleshoot abnormal units or recover balance according to the BMS instructions; check whether the communication cable (such as CAN, RS485) connector between the BMS and the charger is secure.
• Precautions: If the BMS reports a single cell failure, do not force charging; some BMS resets require professional tools or manufacturer support.

7) Check the low-temperature protection and temperature sensor.

• Symptom: Charging fails in cold environments, the charger’s red and yellow lights flash and may be accompanied by temperature-related alarms.
• Possible causes: The battery temperature is below the charging threshold, or the temperature sensor/thermocouple has poor contact or is damaged, resulting in a false low temperature reading.
• Solution: Move the battery to a warm environment and wait for it to return to the allowable temperature; check the temperature sensor connector and wiring harness, and replace the sensor if necessary.
• Precautions: Avoid using open flames or rapid heating of the battery; lithium batteries have low charging efficiency and increased risk at low temperatures, so follow the battery instructions.

8) Check for internal faults in the charger (electronic components/firmware)

• Symptom: After checking the above items, the red and yellow lights are still flashing, the charger is overheating abnormally, or there are abnormal sounds/odors.
• Possible causes: Failure of the charger’s internal power module, rectifier, filter capacitor, relay, or firmware; fan failure triggering over-temperature protection.
• Solution: Send the charger to a professional repair shop or contact the manufacturer’s after-sales service for fault diagnosis and repair (replace the motherboard, fan, or update the firmware).
• Precautions: The charger contains high-voltage components. Do not disassemble it if you are not a professional. If the repair cost is close to or exceeds that of replacing the device, consider replacing it directly.

Additional tips:

• Check the indicator light code table in the charger’s manual; the meaning of flashing red and yellow lights may differ between manufacturers.
• Using a multimeter to measure the charger’s output voltage/current (under safe operating conditions) can quickly determine whether there is a fault on the output side;
• Keeping the charger and battery model/serial number makes contacting manufacturer support more efficient.

When should you replace your charger?

• The charger has been professionally tested and confirmed to have damaged internal key components (such as the rectifier module and motherboard) and the repair cost is close to or exceeds the cost of purchasing a new device.
• The charger is severely aged, frequently experiences intermittent failures, or remains unstable even after multiple repairs;
• The charger is incompatible with existing battery specifications/communication protocols and this issue cannot be resolved through firmware or hardware upgrades.

Three criteria for selecting a charger: 1) Voltage/Chemistry and Power Matching: The output voltage, current, and charging curve must be fully matched to the nominal voltage and chemistry of the battery pack (e.g., a 48V dedicated charger for 48V LiFePO4). 2) BMS and Communication Compatibility: If the battery has a BMS, prioritize “smart chargers” that support similar communication protocols (CAN, RS485, etc.) and can work in conjunction with the BMS. 3) Safety Certification and Weather Resistance: Choose branded products with CE/UL certifications, appropriate IP ratings (if used outdoors), over-temperature/over-current/over-voltage/reverse connection protection, and a reasonable warranty period.