Operation CHARM: Car repair manuals for everyone.
Home >> GMC Truck >> 2002 >> K 1500 Truck 4WD V6-4.3L VIN W >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P1870 >> 4L80-E / 4L85-E Automatic Transmission

4L80-E / 4L85-E Automatic Transmission





DTC P1870





Test 1-7





Test 8-12

Circuit Description with 4L80-E / 4L85-E Automatic Transmission
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 Automatic Transmission Input Shaft Speed Sensor (AT ISS), Automatic Transmission Output Shaft Speed Sensor (AT OSS), and other transmission components. The forward clutch housing is used as the AT 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 C DTC. For California emissions vehicles, DTC P1870 is a type B DTC.

Conditions for Running the DTC
^ No MAF sensor DTCs P0101, P0102 or P0103.
^ No MAP sensor DTCsP0106, P0107 or P0108.
^ No TP sensor DTCs P0121, P0122, or P0123.
^ No VSS DTC P0502 or P0503.
^ No ISS DTCsP0716 or P0717.
^ No TCC PWM solenoid valve DTC P1860.
^ No TCC Stuck Off DTC P0741.
^ No TCC Stuck On DTC P0742.
^ No 1-2 SS valve DTCs P0751 or P0753.
^ No TFP manual valve position switch DTC P1810.
^ The engine speed is running for greater than 7 seconds.
^ The system voltage is 8 - 18 volts
^ The throttle angle is 10-100 percent.
^ Engine speed is 1,250 - 5,000 RPM.
^ The engine vacuum is 0 - 105 kPa (0 - 15 psi).
^ The TFT is 20 - 130°C (68 - 266°F).
^ Vehicle speed is 56 - 177 km/h (35 - 110 mph)
^ TFP manual valve position switch indicates D4.
^ Speed ratio is 2.25 - 0.70.
^ The engine torque must be between 108 Nm (80 ft. lbs.) and
- 6.0L: 542 Nm (400 ft. lbs.)
- SAL: 881 Nm (650 ft. lbs.)
^ The TCC is commanded ON for 0.04 second or more.
^ TCC is locked ON for greater than 0.1 second.
^ Commanded gear is 4th.

Conditions for Setting the DTC
The PCM detects slip in the torque converter clutch and/or the fourth gear clutch pack with the TCC in an apply or locked mode. DTC P1870 sets during the second consecutive trip when one of the following condition occurs:

Condition 1
^ The TCC slip speed is 100 - 550 for 10 seconds
^ All conditions for running the DTC are met for three occurrences.

Condition 2
^ The TCC slip speed is 100 - 550 for 1() seconds, the PCM commands maximum line pressure.
^ The TCC slip speed is 100 - 550 for 12.5 seconds, the PCM commands the TCC Off for 2 seconds.
^ The TCC slip speed is 100-550 for 15 seconds.

Action Taken When the MIL/DTC Sets
^ For California emission equipped vehicles, the PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in, which the Conditions for Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated.
^ The PCM commands maximum line capacity.
^ The PCM inhibits the TCC engagement.
^ The PCM freezes shift adapts.
^ The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame, California only, and Failure Records, California and Federal.
The PCM stores the DTC P1870 in PCM history during the second consecutive trip, California, 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 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.
^ For California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 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 or contaminated shift valves may cause intermittent slipping in D4.
^ DTC P1870 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.

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.



pro multis · About Operation CHARM