P1870

Circuit Description
The Transmission Control Module (TCM) monitors the engine speed, the transmission output speed and current gear. The TCM calculates turbine shaft speed and Torque Converter Clutch (TCC) slip speed by using these inputs. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +64 RPM. The table above indicates solenoid states and transmission components that apply during 4th gear with the TCC commanded ON.

When the TCM detects excessive TCC slip when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

Conditions for Running the DTC
^ Transmission is not in P, R, or N.
^ Transmission is not in safety mode.
^ TCC is commanded on.
^ No incorrect gear ratio DTC P0730.
^ The following code enabling and fail conditions are not met:
- P0751 fail cases 1 and 2
- P0752 fail cases 1 and 2
- P0757 fail cases 1 and 2

Condition for Setting the DTC
TCM calculated transmission slip is greater than 288 RPM.

Action Taken When the DTC Sets
^ Early production - The TCM illuminates the service transmission lamp (STL) and sends a MIL request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.
^ Late production - The TCM flashes the Sport Mode Lamp and sends a MIL request on the second consecutive drive trip that the diagnostic runs and fails. The TCM then illuminates the MIL.
^ The ECM records the operating conditions in the Freeze Frame at the time of the MIL request from the TCM.
^ The transmission operates in the default mode (maximum line pressure, command 4th gear, inhibit TCC, freeze shift adapts).

Conditions for Clearing the MIL/DTC
^ Early production - The TCM turns off the STL as soon as the fault is no longer present.
^ Late production - The TCM stops flashing the sport mode lamp as soon as the fault is no longer present.
^ The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL request.
^ A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the MIL/DTC.
^ The TCM cancels the DTC default mode actions when the fault no longer exists and the ignition switch is Off long enough in order to power down the TCM.

Diagnostic Aids
^ Vehicles equipped with Fuel Cap Lamps utilize the Sport Mode lamp to indicate a transmission malfunction. In these vehicles, the Sport Mode Lamp flashes at 200 millisecond intervals when the TCM commands the lamp ON.
^ Vehicles not equipped with Fuel Cap Lamps are equipped with a dedicated Service Transmission Lamp (STL) on the Instrument Panel Cluster (IPC). The STL illuminates steadily when the TCM commands the lamp ON.
^ DTC P0722 could cause DTC P1870 to set falsely.
^ A mechanical failure of the shift solenoids or TCC solenoid valve can set DTC P1870.
^ Internal transmission failures can result in a DTC P1870.
^ Sticking or contaminated shift valves may cause intermittent slipping in D4.
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

Test Description
The number below refers to the step number on the diagnostic table.
3. This step tests the torque converter for slippage while in a commanded lock-up slate.