Allison Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0218

DTC P0218 Step 1 - 6:

Circuit Description for Allison Automatic Transmission
The flow of transmission fluid starts in the transmission pan. It is then drawn through the filter and the transmission case into the oil pump assembly. The oil pump pressurizes the fluid into line pressure that is regulated at the main-pressure regulator valve. From this point fluid is directed to the F Trim Solenoid and to the control-main regulator and control-main relief valve into the control main filter assembly and on to all solenoids for use as control pressure. Hot fluid leaving the torque converter is routed through the converter flow valve to cooler lines and on into the cooler assembly. The transmission oil cooler is located in the radiator. The vehicle may also be equipped with an auxiliary oil cooler. The cooled fluid is resumed to the transmission through the return cooler line and on to the transmission lube circuit. The automatic Transmission Fluid Temperature (TFT) sensor, which is part of PSM assembly, is located in the oil pan.

If the Transmission Control Module (TCM) detects a high TFT for a 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 are active.
The components are powered and ignition voltage is greater than 9V and less than 18 V.
Engine speed is greater than 200 RPM for 5 seconds or more.

Conditions for Setting the DTC
DTC P0218 sets when the TCM detects a transmission sump temperature greater than 122°C (252°F) for 10 seconds or more.

Action Taken When the DTC Sets
The TCM does not illuminate the malfunction indicator lamp, or MIL.
^ DTC P0218 is stored in the TCM history
^ The TCM freezes shift adapts (DNA)
^ The TCM inhibits TCC engagement.
^ The TCM records the operating conditions when the DTC was set. The TCM stores this information as Failure Records.

Conditions for Clearing the MIL/DTC
^ A Scan Tool may be used to clear the code from the TCM history.
^ The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The TCM cancels the DTC default actions when the fault no longer exists and the DTC passes.

Diagnostic Aids
^ 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 and stabilize.
^ DTC P0218 may set after DTC P0711 has set. Follow the diagnostic table for DTC P0711 before proceeding to the diagnostic for DTC P0218. Repairing the condition that set DTC P0711 will likely eliminate DTC P0218.

Test Description
The number refers to the step number on the diagnostic table.
3. This step inspects for air restrictions and loss of transmission fluid flow, causing an extremely high TFT.