Allison - Automatic Transmission

DTC P0712

Circuit Description

The transmission fluid temperature (TFT) sensor is part of the pressure switch manifold (PSM) assembly, and is located in the transmission oil pan. The TFT sensor is a thermistor, which changes value based on the temperature of the transmission fluid. The transmission control module (TCM) supplies a 5-volt reference voltage signal to the TFT sensor and measures the voltage drop in the circuit. When the transmission is cold, the sensor resistance is high and the TCM detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the signal voltage decreases. The TCM uses this information to control shift quality and torque converter clutch (TCC) apply.


DTC P0712 is a type B DTC.


DTC Descriptor

This diagnostic procedure supports the following DTC:


DTC P0712 Transmission Fluid Temperature (TFT) Sensor Circuit - Low Input


Conditions for Running the DTC

* DTC P0711 and P0713 are not active.
* The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
* Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
* The engine has been running for 20 seconds with a coolant temperature above 20°C (68°F).



Conditions for Setting the DTC

DTC P0712 sets when the TCM detects a voltage of less than 313m volts for 2.5 seconds.


Action Taken When the DTC Sets

* The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The TCM uses a TFT default value.
* The TCM freezes shift adapts.
* The TCM stores this information as Failure Records.
* The TCM stores DTC P0712 in TCM history.
* The TCM inhibits TCC engagement.



Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.


Diagnostic Aids

* Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:

- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation

* When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
* You may have to drive the vehicle in order to experience a condition.
* A short to ground allows DTC P0712 to set.
* DTC P0218 may set after DTC P0712 has set. Follow the diagnostic table for DTC P0712 before proceeding to the diagnostics for DTC P0218.



Test Description

The numbers below refer to the step numbers on the diagnostic table.
4. This step tests 5-volt reference.
6. This step tests the TFT sensor and internal wiring harness.
7. This step tests the resistance of the TFT sensor.