Trans Temp Sensor Voltage Too Low (OBD II)

Name of Code:
74 :($4A) - Trans Temp Sensor Voltage Too Low

When Monitored:
Continuously with the key on and engine running.

Set Condition:
The transmission temperature sensor (TTS) signal circuit voltage goes below 1.55 volts for 22 seconds.

Theory of Operation:
The TTS is a positive temperature coefficient (PTC) thermistor type sensor. At cold temperatures the resistance is low and it rises with increased trans oil temperature. The sensor is provided with 5 volt supply from the PCM. The sensor supplies a signal to the PCM ranging from approximately 1.5 volts (cold), to 3.75 volts (hot). Note that when trans temp codes 74 (trans temp low) or 75 (Trans temp high) are set, the PCM will use the engine coolant temperature as a default value for trans temp. Therefore. if one of these codes is set, the trans temp readings should not be used for diagnostic purposes. When the trans temp is below 32°F overdrive and TCC are disabled. When the trans temp is above 262°F, overdrive is disabled and 3rd gear with TCC is used to cool the transmission.

Transmission Effects:
When the transmission is using engine temperature an a default. transmission temperature is calculated using the following equation: engine coolant temp x 0.4375) +87. If no engine coolant temp is available, 180° degrees F. will be substituted. The MIL will not illuminate.

Possible Causes:
- Trans temp sensor signal circuit shorted to ground
- Sensor internal short
- Corroded. camaged, pushed out, miswired, or disconnected connector(s)
- internal controller failure (PCM)