What type of detergent should I use in my WFW9400SW00 washing machine?

You must use only High Efficiency (HE) detergent, which will be marked 'HE' or 'High Efficiency' on the package. Using regular non-HE detergent can create too much sudsing and may result in washer errors, longer cycle times, reduced rinsing performance, component failures, and mold or mildew. Follow the manufacturer's instructions to determine the correct amount of detergent to use.