P2742 Trans Fluid Temp Sensor B Circuit Low Input PXNUMX Trans Fluid Temp Sensor B Circuit Low Input PXNUMX Trans Fluid Temp Sensor B Low Input

P2742 Trans Fluid Temp Sensor B Circuit Low Input PXNUMX Trans Fluid Temp Sensor B Circuit Low Input PXNUMX Trans Fluid Temp Sensor B Low Input

OBD-II DTC Datasheet

Low input signal in the transmission fluid temperature sensor circuit B

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles with a transmission fluid temperature sensor (Jeep, Ford, Nissan, Toyota, Honda, Infiniti, Acura, Jaguar, Lexus and t.D.). Although it is general, the exact repair steps may vary depending on the make / model.

The transmission fluid temperature (TFT) sensor provides a signal that is used by the powertrain control module (PCM) to determine shift points, line pressure, and torque converter clutch (TCC) control. The sensor is often located in the transmission oil pan.

The TFT sensor receives a reference voltage (typically 5 volts) from the PCM. It changes its internal resistance depending on the temperature of the transmission fluid in order to send a reverse voltage signal to the PCM. TFT sensors are a type of negative temperature coefficient (NTC) thermistor. This means that the internal resistance of the sensor is inversely proportional to the oil temperature. The TFT sensor signal voltage decreases when the transmission fluid temperature rises and vice versa.

P2742 is set when the PCM detects a low transmission fluid temperature sensor signal "B". This usually indicates a short circuit in the circuit. Consult your specific manufacturer's service manual to determine which "B" circuit is for your vehicle.

An example of a transmission fluid temperature sensor:

Corresponding Transmission Fluid Temperature Sensor "B" circuit codes:

• P2740 Transmission Fluid Temperature Sensor B Circuit Malfunction
• P2741 Transmission Fluid Temperature Sensor B Circuit Range / Performance
• P2743 High Input Transmission Fluid Temperature Sensor B Circuit
• P2744 Transmission Fluid Temperature Sensor B Malfunction

Code severity and symptoms

The severity of this code is moderate to severe. In some cases, this code may indicate a transmission problem. It is recommended to fix this code as soon as possible.

Symptoms of a P2742 engine code may include:

• The engine warning lamp comes on
• Incorrect operation of the torque converter clutch
• Harsh or delayed shifts
• Car stuck in dead-end mode

reasons

Causes of this DTC may include:

• Defective transmission fluid temperature sensor
• Transmission problems
• Wiring problems
• Defective PCM

Diagnostic and repair procedures

Begin by visually inspecting the transmission fluid temperature sensor and associated wiring. Look for loose connections, damaged wiring, etc. If damage is found, repair as needed, clear the code and see if it returns. Then check the technical service bulletins (TSBs) for the problem. If nothing is found, you will need to proceed to the step-by-step system diagnostics.

The following is a generalized procedure as the testing of this code differs from vehicle to vehicle. To accurately test the system, you need to refer to the manufacturer's diagnostic flowchart.

Pre-test the circuit

Use a scan tool to monitor the transmission temperature sensor data parameter. Disconnect the TFT sensor; the scan tool value should drop to a very low value. Then connect the jumper across the terminals. If the scan tool now displays a very high temperature, the connections are good and the ECM can recognize the input. This means the problem is most related to the sensor and not the circuit or PCM issue.

Check sensor

Disconnect the transmission fluid temperature sensor connector. Then measure the resistance between the two terminals of the sensor with a DMM set to ohms. Start the engine and check the counter value; the values ​​should decrease gradually as the engine warms up (check the engine temperature gauge on the dashboard to make sure the engine is at operating temperature). If the engine temperature rises but the TFT resistance does not decrease, the sensor is defective and must be replaced.

Check circuit

Check the reference voltage side of the circuit: with the ignition on, use a digital multimeter set to volts to check the 5V reference voltage from the PCM at one of the two terminals of the TCM sensor. If there is no reference signal, connect a meter set to Ohm (with the ignition off) between the TFT reference terminal and the PCM reference terminal. If the meter reading is out of tolerance (OL), there is an open circuit between the PCM and the sensor that needs to be located and repaired. If the counter reads a numeric value, there is continuity.

If everything is ok up to this point, you will want to check if 5 volts is coming out of the PCM at the voltage reference terminal. If there is no 5V reference voltage from the PCM, the PCM is probably defective.

Check circuit ground.

Connect a resistance meter (ignition OFF) between the ground terminal on the transmission fluid temperature sensor and the ground terminal on the PCM. If the meter reading is out of tolerance (OL), there is an open circuit between the PCM and the sensor that needs to be located and repaired. If the counter reads a numeric value, there is continuity. Finally, make sure the PCM is well grounded by connecting one meter to the PCM's ground terminal and the other to the chassis ground. Once again, if the meter reads out of range (OL), there is an open circuit between the PCM and ground that needs to be found and repaired.

If everything in the chain is checked, there may be a problem with the transmission. This is especially true if the transmission fluid temperature codes are set in conjunction with other transmission codes.

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