Circuit Description
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 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 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 D DTC. For California emissions vehicles, DTC P1870 is a type B DTC.
Conditions for Running the DTC
| • | No MAP sensor DTCs P0101, P0102 or P0103. |
| • | No MAF sensor DTCs P0106, P0107 or P0108. |
| • | No TP sensor DTCs P0121, P0122, or P0123. |
| • | No OSS DTC P0502. |
| • | The system voltage is 8.0-18.0 volts. |
| • | 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 300 RPM for 7 seconds, and not in fuel cutoff mode. |
| • | The TP sensor is 10-100%. |
| • | Engine speed is 1250-5000 RPM . |
| • | The engine vacuum is 0-105 kPa. |
| • | The TFT is 20° to 130°C (68°-266°F). |
| • | Vehicle speed is 56.3-177 Km/h (35-110 MPH) |
| • | TFP manual valve position switch indicates D4. |
| • | Speed ratio is 1.10-0.70. |
| • | The engine torque is 100 N·m (80 lb ft) to 542 N·m (400 lb ft). |
| • | The TCC is commanded ON for 4 seconds or more. |
| • | TCC is locked ON for greater than 2.5 seconds. |
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 120-550 for 10 seconds. |
| • | All conditions for running the DTC are met for three occurrences. |
Condition 2
The following sequence of events occur:
| • | The TCC slip speed is 120-550 for 10 seconds, the PCM commands maximum line pressure. |
| • | The TCC slip speed is 120-550 for 12.5 seconds, the PCM commands the TCC Off for 2.0 seconds. |
| • | The TCC slip speed is 120-550 for 15.0 seconds. |
Action Taken When the MIL/DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) for California emissions vehicles. |
| • | The PCM commands maximum line capacity. |
| • | The PCM inhibits the TCC engagement. |
| • | The PCM inhibits 4th gear if in hot mode. |
| • | The PCM freezes shift adapts. |
| • | The PCM stores DTC 1870 in PCM History. |
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 consecutive 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 consecutive 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. |
| • | 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.
-
This step tests the indicated range signal to the actual selected range. A faulty TFP manual valve position switch can set a DTC P1870.
-
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.
-
This step tests for excessive TCC slip speed while in a commanded TCC lock-up state and in third gear.
-
This step tests for a sticking TCC shift valve.
-
This step tests for proper transmission line pressure.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
2 | Perform the Transmission Fluid Checking Procedure. Refer to Transmission Fluid Check . Was the Transmission Fluid Checking Procedure performed? | -- | Go to Transmission Fluid Check | |||||||||
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Does each selected transmission range match the scan tool TFP switch A/B/C display? (Refer to the Range Signal table.) | -- | |||||||||||
Drive the vehicle under the following conditions:
At any time is the TCC slip speed greater than the specified value for 10 seconds? | 120 RPM | Go to Diagnostic Aids | ||||||||||
Drive the vehicle under the following conditions:
At any time is the TCC slip speed greater than the specified value for 10 seconds? | 120 RPM | |||||||||||
Repeat the procedure in step 4. Drive the vehicle under the following conditions:
Is the TCC slip speed greater than the specified value? | 120 RPM | |||||||||||
7 | Refer to Symptom Diagnosis Slipping TCC. Was the condition corrected? | -- | -- | |||||||||
Refer to Line Pressure Check . Is the line pressure within specifications? | -- | Go to Symptom Diagnosis Low Line Pressure | ||||||||||
9 |
Refer to Automatic Transmission Fluid and Filter Replacement. Is the fluid or the pan contaminated? | -- | Go to Unit Repair | |||||||||
10 |
Was the condition found? | -- | ||||||||||
11 | Inspect the following components for contamination or sticking.
Was the condition found? | -- | Go to Unit Repair | |||||||||
12 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
