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 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 10-40 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 0.90-1.375. |
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 off 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 Conditions and Poor Connections in Wiring Systems. |
| • | Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems. |
| • | 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 | Did you perform the Powertrain Diagnostic System Check? | -- | ||||||||||||||||||||||
Important: Before clearing the DTC, 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 |
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. Test the power feed circuit (CKT 439) from the AT inline harness connector to the fuse block for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |||||||||||||||||||||
6 | Test the TCC solenoid valve control circuit (CKT 422) from the AT inline harness connector to the PCM for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||||||||||||||
7 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls. Did you complete the replacement? | -- | -- | |||||||||||||||||||||
Perform the Transmission Fluid Check . Did you complete the procedure? | -- | -- | ||||||||||||||||||||||
9 |
Refer to Transmission Control Replacement . Did you find and correct the condition? | -- | ||||||||||||||||||||||
10 | 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 . Did you find and correct the condition? | -- | ||||||||||||||||||||||
Inspect for low transmission line pressure. Refer to Line Pressure Check . Is the line pressure within specifications? | -- | |||||||||||||||||||||||
12 | Inspect for the following potential sources of the low line pressure:
Refer to Transmission Overhaul in the 3T40-E Section of the Transmission Unit Repair Manual. Did you find and correct the condition? | -- | -- | |||||||||||||||||||||
13 | Inspect the TCC hydraulic circuit for the following conditions:
Refer to Transmission Overhaul in the 3T40-E Section of the Transmission Unit Repair Manual. Did you find and correct the condition? | -- | ||||||||||||||||||||||
14 | Inspect the torque converter for the following conditions:
Refer to Transmission Overhaul in the 3T40-E Section of the Transmission Unit Repair Manual. Did you find and correct the condition? | -- | ||||||||||||||||||||||
15 | Inspect the direct clutch for the following conditions:
Refer to Transmission Overhaul in the 3T40-E Section of the Transmission Unit Repair Manual. Did you find and correct the condition? | -- | ||||||||||||||||||||||
16 | Inspect the forward clutch for the following conditions:
Refer to Transmission Overhaul in the 3T40-E Section of the Transmission Unit Repair Manual. Did you find and correct the condition? | -- | -- | |||||||||||||||||||||
17 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
