Powertrain, generic (extended)

P2742 Transmission Fluid Temperature Sensor B Circuit Low

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

P2742 reports that the sensor B signal sits below its valid range, and how low is defined differs by maker. GM's 2023/24 dual-clutch TCM treats a cooler temperature sensor value under 200 mV, with hysteresis, for at least 500 ms as too low, Type B; for the usual NTC thermistor that equals an extremely hot reading or a signal wire shorted to ground. Ford's TR9070 lists P2742 as the out-of-window-low test of its cooler-out sensor. Mitsubishi's 2009 Twin Clutch SST instead relates Low to the computed temperature: −40 °C or colder for 400 ms, naming the transaxle-integrated unit as suspect. Real overheating with a sound sensor belongs to P273F. Afterwards the module ignores sensor B and uses a substitute.

Likely causes

Signal lead of sensor B chafed through and touching ground
Sensor B shorted internally
Control unit with built-in sensor faulty (Mitsubishi TC-SST)

Symptoms

  • Warning lamp after two trips on GM
  • Scan tool shows sensor B extremely hot (GM, Ford) or extremely cold (Mitsubishi)
  • Protective strategy with substitute temperature

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–2,500
Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

trans fluid temp sensor bwiring harness

Related codes

P2740P2741P2743P2744P273FP0712

References: gsi.ext.gm.com, mitsubishitechinfo.com, fordservicecontent.com.