4L80-E / 4L85-E Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The flow of transmission fluid starts in the transmission bottom pan. Fluid is drawn through the filter and transmission case into the oil pump assembly. The oil pump assembly pressurizes the fluid (line pressure), which becomes the main supply line of fluid. This fluid is directed to various components and hydraulic circuits within the transmission. The pressure regulator valve receives this fluid and directs it to the converter clutch shift valve. The converter clutch shift valve directs hot fluid leaving the torque converter or regulated converter feed fluid, through the cooler line to the transmission oil cooler. The transmission oil cooler is located in the radiator. The vehicle may also be equipped with an auxiliary oil cooler. The cooled fluid (center lube) is returned to the transmission through the return cooler line and into center lube port of the transmission. The automatic Transmission Fluid Temperature (TFT) sensor, senses the fluid temperature in the transmission bottom pan.

If the Vehicle Control Module (VCM) detects a high TFT for a long period of time, then DTC P0218 sets. DTC P0218 is a type C DTC.

CONDITIONS FOR RUNNING THE DTC
No TFT sensor DTCs P0711, P0712 or P0713.

CONDITIONS FOR SETTING THE DTC
The TFT is greater than 130°C (266°F) for 600 seconds (10 minutes).

ACTION TAKEN WHEN THE DTC SETS
^ The VCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The VCM freezes shift adapts from being updated.
^ The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Failure Records.
^ The VCM stores DTC P0218 in VCM history.

CONDITIONS FOR CLEARING THE DTC
^ A scan tool clears the DTC from VCM history.
^ The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
^ Inspect the cooling system fluid level and condition.
^ Verify the customer's driving habits, such as trailer towing, etc...
^ The scan tool Transmission Fluid Temperature (TFT) should rise steadily during warm-up cycles then stabilize.
^ Refer to Symptom Diagnosis. Symptom Related Diagnostic Procedures

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
3. This step inspects for air restrictions and loss of transmission fluid flow, causing an extremely high TFT.