P1870

Circuit Description
The Powertrain Control Module (PCM) monitors the engine speed, and the transmission Output Shaft Speed. The PCM calculates turbine shaft speed and Torque Converter Clutch (TCC) slip speed by using inputs from the transmission Input Shaft Speed (ISS) sensor, transmission Output Shaft Speed (OSS) sensor and other transmission components. The forward clutch housing is used as the Input Speed Sensor (ISS) rotor. Whenever the TCC is engaged, engine speed and turbine speed will closely match, indicating low TCC slip speed. In D3 with the TCC engaged, calculated transmission component slip can only occur in the torque converter. In D4 overdrive with the TCC engaged, transmission component slip can occur in the TCC or the fourth clutch assembly.

If the PCM detects an excessive TCC slip speed in D4 overdrive, when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type D DTC. For California emissions vehicles, DTC P1870 is a type B DTC.

Conditions for Running the DTC
^ No MAP DTCs P0106, P0107 or P0108.
^ No engine speed DTC P0335.
^ No A/T ISS sensor DTCs P0716 or P0717.
^ No OSS sensor DTCs P0722 or P0723.
^ No TCC PWM solenoid valve DTCs P0741, P0742, or P1860.
^ No 1-2 SS valve DTCs P0751 or P0753.
^ No 2-3 SS valve DTCs P0756 or P0758.
^ No TFP manual valve position switch DTC P1810.
^ The gear range is D4.
^ The Accelerator Pedal Position (APP) angle is 12-80%.
^ The TFT is +20° to +130°C (68°-266°F).
^ The engine speed is 1200-3750 RPM.
^ System voltage is 8.0-18.0 volts.
^ The vehicle speed is 48-176 km/h (30-110 mph).
^ The engine torque is 95-644 N.m (70-475 lb ft).

Conditions for Setting the DTC
The above conditions are met for Running the DTC, with 4th gear commanded and the TCC ON and one of the following conditions occur:

Condition 1 (after 3 Occurrences)
The PCM detects a slip speed of 120-525 RPM for greater than 6.0 seconds.

Condition 2 (In the following sequence for one occurrence)
^ The PCM detects a TCC slip speed of 110-500 RPM for 10 seconds.
- The PCM commands maximum line pressure.
- The PCM freezes shift adapts.
^ The PCM detects a TCC slip speed of 110-500 RPM for 10 seconds.
- The PCM commands the TCC OFF for 1.5 seconds.
- The PCM commands the TCC ON.
^ The PCM detects a TCC slip speed of 11-500 RPM for 10 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL).
^ The PCM commands maximum line pressure.
^ The PCM inhibits the TCC engagement.
^ The PCM inhibits 4th gear if in hot mode.
^ The PCM freezes shift adapts.
^ The PCM stores DTC P8170 in PCM history.

Conditions for Clearing the MIL/DTC
^ For Federal and California emissions, the PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool clears the DTC from PCM history.
^ For Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ For vehicles equal to or greater than 15,000 lbs GVW, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
^ A TFP manual valve position switch malfunction can set DTC P1870.
^ A mechanical failure of the shift solenoids or TCC PWM solenoid valve can set DTC P1870.
^ Internal transmission failures can result in a DTC P1870.
^ Sticking shift valves or contamination may cause intermittent slipping in D4.
^ First, diagnose and clear any engine DTCs that are present. Then inspect for any transmission DTCs that may have reset.
^ DTC P1860 can cause a DTC 1870 to set. Diagnose the electrical codes first.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests the indicated range signal to the actual selected range. A faulty TFP manual valve position switch can set a DTC P1870.
4. This step tests for excessive TCC slip speed while in a commanded TCC lock-up state and in fourth gear; and confirms that the fault is present.
5. This step tests for excessive TCC slip speed while in a commanded TCC lock-up state and in third gear.
6. This step tests for a sticking TCC shift valve.
8. This step tests for proper transmission line pressure.