Circuit Description
The primary source of heat in an automatic transmission is the torque converter. In the 5L40-E transmission, hot fluid exits the torque converter through the torque converter clutch (TCC) control valve and flows to the transmission cooler supply line. The supply line connects to the cooler, which is located in the radiator. From the cooler, the fluid returns through the fluid cooler return line and enter the lubrication circuits. After lubricating the internal components, the fluid returns to the transmission fluid pan. The fluid pump draws fluid through the filter from the fluid pan, where the transmission fluid temperature (TFT) sensor is located. The fluid pump pressurizes the fluid and directs it to the pressure regulator valve. The pressure regulator valve is the starting point for the main supply of fluid to the torque converter and the transmission hydraulic components.
The TFT sensor is part of the automatic transmission internal wiring harness assembly. The TFT sensor is a thermistor or a resistor that changes value when the temperature changes. The sensor has a negative temperature coefficient, which means that as the temperature increases, the sensors internal resistance decreases. As the temperature decreases, the sensors internal resistance increases.
The transmission control module (TCM), supplies a 5-volt reference signal to the sensor via terminal X1-15 and measure the voltage drop in the circuit.
When the transmission fluid is cold, the sensor's resistance is high and the TCM detects a high signal voltage. As the fluid temperature increases, the internal resistance of the sensor decreases, which in turn lowers the signal voltage.
When the transmission fluid is cold, the sensor's resistance is high and the TCM detects a high signal voltage. As the fluid temperature increases, the internal resistance of the sensor decreases, which in turn lowers the signal voltage.
When the TCM detects high transmission fluid temperature for an extended period of time, DTC P0218 sets which is a type 'C' DTC.
Conditions for Running the DTC
| • | The transmission fluid temperature is -39 to +149°C for greater than 5 seconds. |
| • | Ignition voltage is between 8-18 volts. |
Conditions for Setting the DTC
The TCM senses the transmission fluid is 132°C or greater for 600 seconds (10 minutes).
Action Taken When the DTC Sets
| • | The TCM does not request the powertrain interface module (PIM) to illuminate the check powertrain malfunction indicator lamp (MIL). |
| • | The TCM records the operating conditions when the 'Conditions for Setting the DTC' are met. The TCM records this information as a Failure Record. |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P0218 into TCM history. |
Conditions for Clearing the MIL/DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM cancels the DTC default actions when the condition no longer exists. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
Diagnostic Aids
Check if the instrument cluster displays any conditions relating to the engine cooling system, as high engine temperatures will affect the cooling systems capacity to cool the transmission fluid.
On Tech 2, scroll to Transmission Fluid Temperature data list parameter. While driving the vehicle, the fluid temperature should rise steadily to a normal operating temperature, then stabilize.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Checks for transmission mechanical conditions that could be causing the transmission fluid temperature sensor to sense high fluid temperature.
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Checks for transmission mechanical conditions that could be causing the transmission fluid temperature sensor to sense high fluid temperature.
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Checks for transmission mechanical conditions that could be causing the transmission fluid temperature sensor to sense high fluid temperature.
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Checks for transmission mechanical conditions that could be causing the transmission fluid temperature sensor to sense high fluid temperature.
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Checks for transmission mechanical conditions that could be causing the transmission fluid temperature sensor to sense high fluid temperature.
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Checks for short to voltage on the sensor signal circuit.
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Checks for short to ground on the sensor signal circuit.
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Checks for open circuit on the sensor signal circuit.
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Checks for internal shorting of the transmission wiring harness from the TCM connector to the transmission wiring harness connector X121-X1.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on Testing Wiring Faults, refer to Wiring Systems. | ||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | Go to Step 2 | ||
Is the engine coolant temperature above the specified value when the DTC is set? | 125°C | Go to Step 3 | ||
Did you perform the fluid level checking procedure and is the level now OK? | Go to Step 4 | Go to Transmission Fluid Check | ||
Inspect the transmission cooling system for restrictions or damage. Refer to Transmission Fluid Cooler Flushing and Flow Test. Did you find a problem with the cooling system? | Repair or replace cooling system components as necessary. Go to Step 17 | Go to Step 5 | ||
Check the transmission line pressure. Refer to Line Pressure Check. Did you find a problem with the transmission line pressure? | Remove and repair the transmission as necessary. Go to Step 17 | Go to Step 6 | ||
Test the torque converter for a seized stator. Refer to Torque Converter Diagnosis. Did you find a problem with the torque converter? | Remove and replace the torque converter as necessary. Go to Step 17 | Go to Step 7 | ||
Is the voltage reading less than the specified value? | Less than 0.3 volts | Go to Step 9 | Go to Step 8 | |
8 |
Does either check indicate a short to voltage in the wiring? | Repair short to voltage in relevant circuit Go to Step 17 | Go to Step 16 | |
Using a digital ohmmeter, measure the resistance between the TCM wiring harness connector A112-T68, terminal X1-15 and a sound ground. Is the resistance greater than the specified value? | Greater than 500 kΩ | Go to Step 11 | Go to Step 10 | |
10 | Using a digital ohmmeter check transmission wiring for short to ground between the TCM transmission wiring harness connector A112-T68, terminal X1-15 and the transmission wiring harness connector X121-X1, terminal X1-10. Does either check indicate a short to ground in the wiring? | -- | Repair short to ground in relevant circuit Go to Step 17 | Go to Step 16 |
Is the resistance within specified values with the transmission fluid temperature between 0-150°C? | -- | Go to Step 15 | Go to Step 12 | |
12 | Is the resistance greater than the specified value? | 0.37-65 kΩ | Go to Step 14 | Go to Step 13 |
Does either check indicate an internal short circuit in the wiring? | -- | Repair internal short circuit in relevant circuit. Go to Step 17 | Go to Step 16 | |
14 |
Does either check indicate an open circuit in the wiring? | -- | Repair open in relevant circuit. Go to Step 17 | Go to Step 16 |
15 | Replace the TCM. Refer to Transmission Control Module Replacement. Is the repair complete? | -- | Go to Step 17 | |
16 |
Is wiring harness damaged? | -- | Carry out repairs as necessary. Go to Step 17 | Transmission fluid temperature sensor faulty. Replace transmission internal wiring harness assembly. Go to Step 17 |
17 | Perform the following operation to verify the repair:
Does the DTC reset? | -- | Go to Step 18 | Go to Step 2 |
18 | Use Tech 2 to read DTC information. Does Tech 2 display any DTCs that have not been diagnosed rectified? | -- | Go to the Vehicle System Diagnostics that belongs to the undiagnosed DTC. | System OK |
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||
