With 4L80 Transmission

Diagnostic Chart:

Circuit Description
The Vehicle Control Module (VCM) monitors the difference in the engine speed, the turbine speed, and the transmission input shaft speed. In D3 drive range with the torque converter clutch engaged, the engine speed should closely match the input shaft speed (turbine speed). IN D4 drive range with the TCC engaged, the TCC slip speed should be -25 to +30 RPM. If the VCM detects an excessive slip in the TCC and/or the fourth gear clutch with the TCC 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 Setting the DTC
The following conditions are met for 10 seconds with 4th gear commanded and the TCC ON.

^ No Engine Speed DTC P0335.
^ No TP Sensor DTCs P0121, P0122, or P0123.
^ No Output Shaft Speed (OSS) DTC P0502.
^ No Automatic Transmission Input Shaft Speed (A/T ISS) Sensor DTCs P0716 or P0717.
^ No TCC PWM Sol. 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 Val. Position Sw. DTCs P1810.
^ TFP Val. Position Sw. indicates D4.
^ The TP Sensor is 12 - 45%.
^ The engine vacuum is 0-105 kPa.
^ The engine torque is 100 N.m (80 lb. ft) to the following:

- 470 Nm (265 lb ft).

^ The TCC is commanded ON for greater than 1 second.
^ The Transmission Fluid Temperature (TFT) is -10 to +130°C (14-266°F).
^ The Shift Solenoid performance counters are clean.
^ The TCC is fully locked for greater than 0.5 seconds.
^ The VCM commands maximum TCC capacity.
^ The VCM detects a slip speed of greater than 130 RPM.

Action Taken When the DTC Sets

^ The VCM inhibits the TCC engagement.
^ The VCM inhibits 4th gear if in hot mode.
^ The VCM freezes shift adapts.

^ The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.

Conditions for Clearing the DTC

1. For California emissions vehicles, the VCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.
2. A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
3. The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids

^ A TFP Val. Position Sw. malfunction can set DTC P1870.
^ A mechanical failure of the shift solenoids or TCC PWM Sol. 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 or TP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

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 Valve Position Switch can set a DTC P1870.
4. This step tests for proper transmission line pressure.
5. This step tests for slippage while in a commanded lock-up state and in fourth gear; and confirms that the fault is present.
6. This step tests the torque converter for slippage while in a commanded lock-up state and in third gear.
7. This step tests for a sticking shift valve.