Fault codes covered
51-01
The outdoor air thermistor determines operating range of compressor and fan speeds in cooling and heating operating modes. When “OAT Open” fault is active, the OCT 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 above 465kohm for 1 second this fault will occur. Once sensor value drops below 465kohm for 1 second the fault will clear. This fault does not escalate to a malfunction.
If the resistance value of OAT thermistor is higher 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 above 465kohm, look for a break in the wiring or at the connector itself. If no breaks are observed, replace sensor. If measured resistance is within allowable range, replace PCM.
Source: ACHPVSR454-02SM troubleshooting pages.