Allison Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0218
Circuit Description for Allison Automatic Transmission
The flow of transmission fluid starts in the transmission pan. The fluid is then drawn through the filter and transmission case and into the oil pump assembly. The oil pump pressurizes the fluid into main pressure that is regulated at the main pressure regulator valve. From this point, fluid is directed to the torque converter clutch pulse width modulated (TCC PWM) 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 into the cooler assembly. The transmission oil cooler is located in the radiator. The vehicle may be equipped with auxiliary oil cooler. The cooled fluid is returned to the transmission through the return cooler line and to the transmission lube circuit. The automatic transmission fluid temperature (TFT) sensor, which is part of pressure switch manifold (PSM) assembly, is located in the oil pan. If the transmission control module (TCM) detects a high TFT for an extended period of time, then DTC P0218 sets.

DTC P0218 is a type C DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0218 Transmission Fluid Over temperature

Conditions for Running the DTC
^ DTCs P0711, P0712, 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 for greater than 5 seconds.

Conditions for Setting the DTC
DTC P0218 sets when the TCM detects a transmission sump temperature greater than 126°C (252°F) for 10 seconds.

Action Taken When the DTC Sets
^ The TCM does not illuminate the malfunction indicator lamp (MIL).
^ The TCM freezes shift adapts from being updated.
^ The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.
^ The TCM stores DTC P0218 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.
^ The TCM cancels the DTC default actions when the condition no longer exists and the DTC passes the test.

Diagnostic Aids
^ Verify the driving habits of the customer, such as trailer towing, etc.
^ The scan tool TFT should rise steadily during warm-up cycles, then 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 below refers to the step number on the diagnostic table.
3. This step inspects for air restriction and loss of transmission fluid flow, causing an extremely high TFT.