4L80-E / 4L85-E Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Vehicle Control Module (VCM) monitors the engine speed, and the transmission output shaft speed. The VCM calculates turbine shaft speed and Torque Converter Clutch (TCC) slip speed by using inputs from the transmission Input (shaft) Speed Sensor (ISS), transmission Output (shaft) Speed Sensor (OSS), and other transmission components. The forward clutch housing is used as the 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 VCM detects an excessive TCC slip speed in D4 OVERDRIVE, when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type C DTC. For California emissions vehicles, DTC P1870 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
The following conditions occur 3 times for 10 seconds:
^ No MAP sensor DTCs P0101, P0102 or P0103.
^ No MAF sensor DTCs P0106, P0107 or P0108.
^ No engine speed DTCs P0335, P0336, P0337, or P0338.
^ No TP sensor DTCs P0121, P0122, or P0123.
^ No OSS DTC P0502.
^ No ISS DTCs P0716 or P0717.
^ 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 DTCs P1810.
^ The engine speed is greater than 475 RPM for 7 seconds, and not in fuel cutoff mode.
^ The TP sensor is 7-80%.
^ Engine speed is 1250-5500 RPM.
^ The engine vacuum is 0-105 kPa.
^ The TFT is 20-130°C (68-266°F).
^ Vehicle speed is 56.3-177km/h (35-110 MPH).
^ TFP manual valve position switch indicates D4.
^ Speed ratio is 1.30-0.70 for 5.7L and 7.4L.
^ The engine torque is 100 N.m (80 lb ft) to the following:
- 542 N.m (400 lb ft) 5.7L
- 677.5 N.m (500 lb ft) 7.4L
^ The TCC is commanded ON for 5 seconds or more.
^ TCC duty cycle is greater than 95%.

CONDITIONS FOR SETTING THE DTC
^ All conditions for running the DTC are met for 10 seconds for 3 occurrences.
^ The VCM detects a slip speed of:
- 120-550 RPM. (5.7L)
- 110-550 RPM. (7.4L)

ACTION TAKEN WHEN THE MIL/DTC SETS
^ For California emission equipped vehicles the VCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Non-California emission equipped vehicles the Malfunction Indicator Lamp (MIL) is not illuminated.
^ The VCM commands maximum line capacity.
^ The VCM inhibits the TCC engagement.
^ The VCM inhibits 4th gear if in hot mode.
^ The VCM freezes shift adapts.
^ The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame (Calif. only) and Failure Records (Calif. and Federal).
^ The VCM stores the DTC 1870 in VCM history during the second consecutive trip (Calif.) or the first trip (Federal) in which the Conditions for Setting the DTC are met.

CONDITIONS FOR CLEARING THE MIL/DTC
^ For California emissions, the VCM 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.
^ For California emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
^ 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 or contaminated shift valves may cause intermittent slipping in D4.

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.