Allison 1000 & 2000 Gen 4 Fault Codes: P0218 Transmission Fluid Over Temperature Condition

CIRCUIT DESCRIPTION:
The flow of transmission fluid starts in the transmission pan. Fluid is then drawn through the filter and internal passages 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 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 into the cooler assembly. The transmission oil cooler is located in the radiator. The vehicle may be equipped with an 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 the PSM, 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.

CONDITIONS FOR RUNNING THE DTC:
1. DTCs P0711, P0712, P0713 are not active.
2. The components are powered, and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
3. Engine speed is greater than 200 rpm for more 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:
1. The TCM does not illuminate the CHECK TRANS light.
2. The TCM freezes shift adapts (DNA).
3. The TCM records the operating conditions when the CONDITIONS FOR SETTING THE DTC: are met. The TCM stores this information as Failure Records.
4. DTC P0218 is stored in the TCM history.
5. The TCM defaults to “hot mode” shift schedule where 4th-range is held and TCC is inhibited to increase engine speed and improve cooler flow.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
1. A Scan Tool may be used to clear the code from the TCM history.
2. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.
3. The TCM cancels the DTC default actions when the fault no longer exists, and the DTC passes test.

DIAGNOSTIC AIDS:
1. Verify the customer’s driving habits, such as trailer towing, etc.
2. The Scan Tool transmission fluid temperature (TFT) should rise steadily during warm-up cycles and then stabilize.
3. DTC P0218 may set after DTC P0711 (not active) has set. Follow the diagnostic information for DTC P0711 before proceeding to the diagnostic for DTC P0218. Repairing the condition that set DTC P0711 will likely eliminate DTC P0218.