Download 1997 Buick LeSabre DTC P1870 Transmission Component Slipping Circuit Description The Powertrain Control Module (PCM) monitors the Torque Converter Clutch (TCC) slip by calculating the difference between the engine speed and the transmission output shaft speed. If the PCM detects an excessive amount of slip when the TCC is engaged, then DTC P1870 sets. DTC P1870 is a type A DTC. Action Taken When the DTC Sets. The PCM inhibits TCC operation. The PCM inhibits 4th gear, if the transmission is in the hot mode. The PCM illuminates the Malfunction Indicator Lamp (MIL). Conditions for Clearing the MIL/DTC The PCM turns OFF the MIL after three consecutive ignition cycles without a failure reported. A scan tool can clear the DTC from the PCM history. The PCM clears the DTC fro m the PCM history if the vehicle completes 40 warm-up cycles without a failure reported. The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM. Diagnostic Aids. Ensure that the vehicle’s final drive ratio matches the PCM’s calibration. Ensure that the transmission will shift through all four gears with the gear select lever in the D4 range. Test Description The numbers below refer to the step numbers on the diagnostic chart. 4. This Step inspects the modulator assembly, which could cause P1870 to set. 5. These are the components that could cause P1870 to set.