For 1990-2009 cars

### Circuit Description

The transmission fluid temperature (TFT) sensor is a positive temperature coefficient thermistor (temperature sensitive resistor) that provides information to the transmission control module (TCM) regarding transaxle fluid temperature. The temperature sensor is located in valve body. Calculated temperature is a factor used to determine the shift time and shift delay time.

The internal electrical resistance of the sensor varies in relation to the operating temperature of the transaxle fluid.

The TCM sends a 5-volt reference signal to the temperature sensor and measures the voltage rise in the electrical circuit. A higher fluid temperature creates a higher resistance in the temperature sensor, thereby measuring a higher voltage signal.

The TCM measures this voltage as another input to help control line pressure, shift schedules and TCC apply. When transaxle fluid temperature reaches 120°C (248°F) the TCM enters "hot mode". At greater temperatures the TCM modifies transaxle shift schedules and TCC apply in an attempt to reduce fluid temperature by reducing transaxle heat generation.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0218 Transmission Fluid Overtemperature

### Conditions for Setting the DTC

• | The calculated temperature is compared with the predetermined min. and max. value.

• | If the temperature is less than min. value or greater than max value then the current temperature is regarded as of range and the corresponding error but will be set.

### Action Taken When the DTC Sets

• | No lamp control required but diagnostic information should be stored immediately when malfunction is detected.

• | TCM assumes the transaxle fluid temperature is 60°C (124°F).

• | No influence on driveability.

### Conditions for Clearing the MIL/DTC

Using a scan tool can clear history DTCs.

### Diagnostic Aids

When DTC P0218 sets, the possible cause of fault could be Transaxle Temperature Sensor.

#### DTC P0218

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Automatic Transmission
2 |

1. Install the scan tool.
2. Turn the ignition ON, with the engine OFF.
3. Record then clear DTCs.
4. Turn the ignition OFF, then turn the ignition ON.
5. Select TFT on the scan tool.
6. Drive the vehicle and observe the scan tool for either of the flowing conditions:

• | The transmission fluid temperature (TFT) does not change more than 1.5°C (2.7°F) in 80 seconds since start-up.

• | The TFT changes more than 20°C (36°F) within 7 seconds, which is an unrealistic change.

Did either of the fail conditions occur?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn the ignition OFF.
2. Disconnect the transaxle wiring connector.
3. Measure the resistance between terminals 9 and 4 of the transaxle wiring connector.

Is the resistance at the specified value?

TFT 25°C (77°F) 990 ohms

Go to Step 7

Go to Step 4

4 |

1. Remove the oil pan.
2. Disconnect the wiring connector of the transaxle fluid temperature sensor.
3. Inspect the automatic transaxle wiring harness for an intermittent short or open.

Was a problem found?

--

Go to Step 5

Go to Step 6

5 | Replace the automatic transaxle wiring harness. Is the replacement complete? | -- | System OK | --
6 | Replace the TFT sensor. Is the action complete? | -- | System OK | --
7 |

1. Disconnect the automatic transaxle wiring connector and disconnect the wiring connector of the transmission control module (TCM).
2. Measure the resistance between terminal 4 of the transaxle wiring connector and terminal B1 of the TCM wiring connector.
3. Measure the resistance between terminal 9 of the transaxle wiring connector and terminal A4 of the TCM wiring connector.

Is the resistance approximately equal to the specified value?

0 ohms

Go to Step 9

Go to Step 8

8 |

1. Inspect the automatic transaxle wiring harness for an intermittent short to ground or open condition.
2. Inspect the automatic TFT sensor wiring harness for an intermittent short to ground or open condition.
3. Repair the circuits, if necessary

Is the repair complete?

--

System OK

--

9 |

1. Turn the ignition ON.
2. Measure the voltage of terminal A4 of the TCM wiring connector.
3. Measure the voltage of terminal B1 of the TCM wiring connector.

Is the voltage within the specified value?

9-16 V

Go to Step 10

Go to Step 11

10 |

1. Inspect the automatic transaxle wiring harness for an intermittent short to power.
2. Inspect the automatic TFT sensor wiring harness for an intermittent short to power.
3. Repair the circuits, if necessary.

Is the repair complete?

--

System OK

--

11 | Replace the TCM. Refer to Transmission Control Module Replacement . Is the replacement complete? | -- | Go to Step 12 | --
12 |

1. After the repair, use a scan tool "clear info" function and road test the vehicle.
2. Review the "DTC info".

Has the last test failed or is the current DTC displayed?

--

Go to Step 2

System OK