Circuit Description
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 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 10-40%. |
| • | 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 0.90-1.375. |
Conditions for Setting the DTC
DTC P1870 sets during the second consecutive trip in which the following condition occurs:
All of the above conditions are met for one or more times.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM inhibits TCC engagement. |
| • | DTC P1870 stores in PCM history. |
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 clears the DTC from PCM history. |
| • | 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 the ignition is off long enough in order to power down the PCM. |
Diagnostic Aids
| • | Inspect the wiring at the PCM, the automatic transmission 4-way connector and all other circuit connecting points for the following conditions: |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Reduced terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| - | Moisture intrusion |
| - | Corrosion |
| • | 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.
-
This step tests for excessive torque converter slip while the TCC is engaged.
-
Low fluid level may be causing the slipping.
-
Low line pressure may be causing the slipping.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||||||||||||
Important: Before clearing the DTCs, use the Scan Tool in order to record the DTC Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Important: Record the TCC slip speed when the transmission is in third gear, with the TCC enabled or engaged. While the TCC is engaged, is the TCC slip speed greater than the specified value? | 150 RPM | Go to Diagnostic Aids | ||||||||||||||||||||||
3 |
Is the test lamp on? | -- | ||||||||||||||||||||||
4 |
Does the test lamp operate ON and OFF as the TCC solenoid is commanded? | -- | ||||||||||||||||||||||
5 | Inspect circuit 439 from the automatic transmission 4-way connector to the fuse block for an open. Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | -- | |||||||||||||||||||||
6 | Inspect circuit 422 from the automatic transmission 4-way connector to the PCM for an open. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | ||||||||||||||||||||||
7 | Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |||||||||||||||||||||
8 | Replace the PCM. Refer to PCM Replacement/Programming in Engine Controls. Is the replacement complete? | -- | Go to PCM Replacement/Programming in Engine Controls | |||||||||||||||||||||
Perform the Transmission Fluid Check . Is the procedure complete? | -- | Go to Transmission Fluid Check | ||||||||||||||||||||||
10 |
Refer to Transmission Control Replacement . Was the condition found? | -- | ||||||||||||||||||||||
11 | Inspect the throttle valve (TV) cable for the following conditions:
Refer to Automatic Transmission Throttle Valve Cable Replacement or Automatic Transmission Throttle Valve Cable Adjustment . Was the condition found? | -- | ||||||||||||||||||||||
Inspect for low transmission line pressure. Refer to Line Pressure Check . Is the line pressure within specifications? | -- | |||||||||||||||||||||||
13 | Inspect for the following potential sources of the low line pressure:
Refer to Control Valves and Oil Pump Disassemble in the 3T40 Section of the Transmission Unit Repair Manual. Was a condition found? | -- | -- | |||||||||||||||||||||
14 | Inspect the TCC hydraulic circuit for the following conditions:
Was a condition found? | -- | ||||||||||||||||||||||
15 | Inspect the torque converter for the following conditions:
Refer to Unit Repair. Was a condition found? | -- | ||||||||||||||||||||||
16 | Inspect the direct clutch for the following conditions:
Refer to Direct and Forward Clutch Components Disassemble in the 3T40 Section of the Transmission Unit Repair Manual. Was a condition found? | -- | ||||||||||||||||||||||
17 | Inspect the forward clutch for the following conditions:
Refer to Direct and Forward Clutch Components Disassemble in the 3T40 Section of the Transmission Unit Repair Manual. Was a condition found? | -- | -- | |||||||||||||||||||||
18 | Make the necessary repairs. Refer to the 3T40 Section in the Transmission Unit Repair Manual for Repair Instructions. Is the repair complete? | -- | Go to Unit Repair | |||||||||||||||||||||
19 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
