P1870

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The PCM monitors the difference between the engine speed and the transmission output speed. In D3 drive range with the Torque Converter Clutch (TCC) engaged, the engine speed should closely match transmission output speed. In D4 drive range with the TCC engaged, TCC slip speed should be -20 to +20 RPM.

If the PCM detects excessive TCC slip when the TCC should be engaged, in 2 consecutive ignition cycles, then DTC P1870 sets. DTC P1870 is a type B DTC.

Conditions for Setting the DTC

The following conditions are met for three TCC cycles with reported excessive TCC slip conditions:
- No Throttle Position Sensor (TPS) DTCs P0122 or P0123
- No Vehicle Speed Sensor (VSS) DTCs P0502 or P0503.
- No 1-2 SS Valve DTC P0753
- No 2-3 SS Valve DTC P0758
- No 3-2 SS Valve Assy DTC P0785.
- No TFP Valve Position Switch DTC P1810.
- No TCC PWM Solenoid Valve DTC P1860.
- No TCC Solenoid Valve DTC P0740.
- The engine speed is greater than 400 RPM for 5 seconds and not in fuel cutoff.
- The engine torque is 50-450 lb ft.
- The gear range is D4.
- Not in 1st gear
- The TP angle is 8-35%.
- The TFT is 20 to +120°C (68-248°F).
- The TCC is ON for greater than 5 seconds.
- The speed ratio is 0.64-1.20 (Speed ratio is the engine speed divided by the output speed).
- The engine speed is 1000-3000 RPM.
- The vehicle speed is 48-120 km/h (30-75 mph).
- The TCC is at maximum apply for greater than 5 seconds.
- The Shift Solenoid performance counter is zero.
- The TCC slip speed is 200-800 RPM for 7 seconds.

Action Taken When the DTC Sets
- The PCM inhibits TCC engagement.
- The PCM commands maximum line pressure.
- The PCM inhibits 4th gear if in hot mode.
- The PCM freezes shift adapts from being updated.
- 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 from 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
- A TFP Valve Position Switch malfunction could set DTC P1870.
- The following mechanical failures could set DTC P1870:
- A mechanical failure of the shift solenoid valves
- A mechanical failure of the TCC Solenoid Valve
- A mechanical failure of the TCC PWM Solenoid Valve
- Internal transmission failures may set a DTC P1870.
- An engine misfire may erroneously set a DTC P1870.
- Ensure that the final drive ratio matches the PCM's calibration.
- A PRNDL DTC may falsely set a DTC 1870.
- Refer to Range Reference

Test Description

The numbers below refer to the step numbers on the diagnostic chart.
2. This step compares the indicated range signal to the actual selected range. A faulty TFP Valve Position Switch could set a DTC P1870.
3. This step tests for slippage while the torque converter is in a commanded lock-up state.