Trane TVR Pro CO Series Service Manual page 62

2.4 E4: Temperature sensor (T3/T4) error
Digital display output
Description
 Outdoor heat exchanger temperature sensor (T3) error or outdoor ambient temperature sensor (T4) error.
 All units stop running.
 Error code is only displayed on the unit with the error.
Trigger / recover condition
 Trigger condition: The main control board cannot receive the feedback signal of temperature sensor T3 or T4.
 Recover condition: The main control board can receive the feedback signal of temperature sensor T3 or T4.
 Reset method: Resume automatically.
Possible causes
 Temperature sensor not connected properly or has malfunctioned.
 Damaged main PCB.
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