P1870

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

Circuit Description with 3T40 Automatic Transmission
The Powertrain Control Module (PCM) monitors the Torque Converter Clutch (TCC) slip speed. The PCM calculates the difference between the engine speed and the transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed.

When the PCM detects excessive slip of the TCC, the forward clutch, and the direct clutch when the TCC is engaged in 3rd gear, then DTC P1870 sets. DTC P1870 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ No Throttle Position (TP) sensor DTCs P0121, P0122 or P0123.
^ No Vehicle Speed Sensor DTCs P0502 or P0503.
^ The engine speed is 1,500-3,600 RPM.
^ Engine torque is greater than 27 N.m (20 lb ft).
^ The throttle angle is 1O-40 percent.
^ The Torque Converter Clutch (TCC) is on for 5 seconds.
^ The TCC slip speed is greater than 140 RPM for 8 seconds.
^ The vehicle speed is 56-120 km/h (35-75 mph).
^ The speed ratio is 0.9-1,375.

CONDITIONS FOR SETTING THE DTC
The PCM transmission slip counter is greater or equal to one count.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the conditions for setting the DTC are met.
^ The PCM inhibits TCC engagement.
^ The PCM stores DTC P1870 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns off the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool can clear the MIL/DTC.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission-related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition is oft long enough in order to power down the PCM.

DIAGNOSTIC AIDS
^ Inspect the connectors at the PCM, AT inline harness connector and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical intermittents in Diagrams.
^ verify that the final drive ratio is correct for the vehicle.
^ Check for overloading or trailer towing in excess of vehicle capacity.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for excessive torque converter slip while the TCC is engaged.
8. Low fluid level may be causing the slipping.
11. Low line pressure may be causing the slipping.