Fault codes covered
51-02
The outdoor air thermistor determines operating range of compressor and fan speeds in cooling and heating operating modes. When “OAT Shorted” fault is active the OCT value will be substituted in its place, and compressor operating speed will be limited to 2700rpm. Fan speeds will be limited based on OCT value. The sensor is monitored continuously and if resistance is below 1kohm for 1 second this fault will occur. Once sensor value increases above 1kohm for 1 second the fault will clear. This fault does not escalate to a malfunction.
If the resistance value of OAT thermistor is lower than the electrical circuit is capable of measuring, this fault will be generated. Measure resistance value of thermistor at the PCM connector. If value is below 1kohm, look for bare wire, short in the wiring, or at the connector itself. If no bare wires or shorts are observed, replace sensor. If measured resistance is within allowable range, replace PCM.
Source: ACHPVSR454-02SM troubleshooting pages.