GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Blazer - 4WD - RHD 🢒 DTC 🢒 DTC P1870

Object Number: 42275 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The powertrain control module (PCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +50 RPM.

When the PCM detects excessive TCC slip when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

Conditions for Running the DTC
    • No TP sensor DTCs P0122 or P0123.
    • No VSS assembly DTCs P0502 or P0503.
    • No TCC solenoid valve DTC P0740.
    • No 1-2 SS valve DTC P0753.
    • No 2-3 SS valve DTC P0758.
    • No 3-2 SS valve assembly DTC P0785.
    • No TFP manual valve position switch DTC P1810.
    • No TCC PWM solenoid valve DTC P1860.
    • The engine speed is greater than 450 RPM for 5 seconds.
    • The engine is not in fuel cutoff.
    • The engine torque is 50-400 lb ft.
    • The engine vacuum is 0-105 kPa.
    • The TP angle is 20-99 percent.
    • The vehicle speed is 48-131 km/h (30-82 mph).
    • The engine speed is 1500-3000 RPM.
    • The speed ratio is 0.69-0.88 (speed ratio is engine speed divided by the transmission output speed).
    • The gear range is D4.
    • The commanded gear is not 1st gear.
    • The TFT is 20-150°C (68-302°F).
    • The shift solenoid performance diagnostic counters are zero.

Conditions for Setting the DTC

DTC P1870 sets if the following conditions occur for three TCC cycles.

    • The TCC is commanded ON for 5 seconds.
    • The TCC is at 40 percent duty cycle for 5 seconds.
    • The TCC slip speed is 130-800 RPM for 7 seconds.

       Important: The following actions may occur before the DTC sets.

    • If the TCC is commanded ON for 5 seconds, the TCC is at 40 percent duty cycle for 5 seconds, the TP angle is 20-99 percent and the transmission slip counter has incremented to either 1 or 2 (out of 3 to increment the fail counter for the current ignition cycle), then the following slip conditions and actions may increment the fail counter for the current ignition cycle:
        These conditions must occur sequentially.

Condition 1

If the TCC slip speed is 130-800 RPM for 7 seconds, then the PCM will command maximum line pressure and freezes transmission adapt functions.

Condition 2

If Condition 1 is met and the TCC slip speed is 130-800 RPM for 7 seconds, then the PCM will command the TCC Off for 1.5 seconds.

Condition 3

If Condition 2 is met and the TCC slip speed is 130-800 RPM for 7 seconds, then the fail counter on the current ignition cycle is incremented.

The above slip conditions and actions may be disregarded if the TCC is commanded OFF at any time as a result of a driving maneuver (sudden acceleration or deceleration).

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 commands maximum line pressure.
    • The PCM inhibits TCC engagement.
    • The PCM inhibits 4th gear if the transmission is in hot mode.
    • The PCM freezes transmission adapt functions.
    • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
    • 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 warm-up cycles without an emission-related diagnostic fault occurring.
    • The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
    • Bronze material found in the transmission oil pan may indicate stator shaft bushing wear. If bushing wear is suspected, inspect the stator shaft and the input (turbine) shaft for damage.
    • Refer to Symptoms - Automatic Transmission for more information.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the torque converter for slippage while in a commanded lock-up state.

DTC P1870

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls

2

Inspect for correct transmission fluid level.

Refer to Transmission Fluid Check .

Did you perform the fluid checking procedure?

--

Go to Step 3

Go to Transmission Fluid Check

3

  1. Install a Scan Tool .
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, 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.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.

    5. Important: It may be necessary to allow multiple TCC cycles to occur in order to verify a slipping condition. It may also be necessary to ensure the transmission is warm before performing this step.

  5. Drive the vehicle in 4th gear with the TCC commanded ON.

Does the Scan Tool TCC Slip Speed measure within the specified range for 7 seconds?

130-800 RPM

Go to Step 4

Go to Intermittent Conditions in Engine Controls

4
  1. Inspect the torque converter clutch (TCC) solenoid valve for the following conditions:
    2. • Internal malfunction (such as sediment or damage)
    • Damaged seals
  2. Inspect the torque converter clutch pulse width modulation (TCC PWM) solenoid valve for the following conditions:
    3. • Internal malfunction (such as sediment or damage)
    • Damaged seals

Did you find and correct the condition?

--

Go to Step 14

Go to Step 5

5
  1. Inspect the 1-2 shift solenoid (SS) valve for the following conditions:
    2. • Internal malfunction (such as sediment or damage)
    • Damaged seals
    • Refer to Shift Solenoid Leak Test .
  2. Inspect the 2-3 shift solenoid (SS) valve for the following conditions:
    3. • Internal malfunction (such as sediment or damage)
    • Damaged seals
    • Refer to Shift Solenoid Leak Test .
  3. Inspect the 3-2 shift solenoid valve assembly for the following conditions:
    4. • Internal malfunction (such as sediment or damage)
    • Damaged seals
    • Refer to Shift Solenoid Leak Test .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 6

6
  1. Inspect the valve body assembly for a stuck regulator apply valve.
  2. Inspect the valve body assembly for a scored regulator apply valve body.

    3. Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 7

7

Inspect the torque converter assembly for the following conditions:

    • Front stator shaft bushing for wear
    • Stator roller clutch not holding
    • External damage/leaks

Did you find and correct the condition?

--

Go to Step 13

Go to Step 8

8

Inspect the oil pump assembly for the following conditions:

    • A stuck converter clutch valve
    • The converter clutch valve is assembled backwards
    • A mispositioned converter clutch valve retaining ring
    • A cocked converter clutch outer valve spring
    • A mispositioned pump to case gasket
    • Restricted orifice cup plugs
    • Damaged orifice cup plugs
    • Over-tightened, or unevenly tightened pump body to cover bolts

Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9

Inspect the input housing and shaft assembly for the following conditions:

    • Cut turbine shaft O-ring seal
    • Damaged turbine shaft O-ring seal
    • Restricted turbine shaft retainer and ball assembly
    • Damaged turbine shaft retainer and ball assembly

Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

10

Inspect the 2-4 band assembly for the following conditions:

    • Worn 2-4 band
    • Damaged 2-4 band
    • Mispositioned 2-4 band
    • Misassembled 2-4 band
    • The band anchor pin is not engaged.
    • Restricted apply passages in the 2-4 servo assembly
    • Blocked apply passages in the 2-4 servo assembly
    • Nicks or burrs on the servo pin
    • Nicks or burrs on the pin bore in the case
    • Damaged fourth servo piston
    • Misassembled fourth servo piston
    • Damaged band apply pin
    • Incorrect band apply pin
    • Damaged servo bore in the case
    • Missing piston seals
    • Cut piston seals
    • Damaged piston seals
    • Porosity in the pistons
    • Porosity in the cover
    • Porosity in the case
    • Damaged piston seal grooves
    • Plugged orifice cup plug
    • Missing orifice cup plug

Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

11

Inspect the forward clutch assembly for the following conditions:

    • Worn clutch plates
    • Porosity in the forward clutch piston
    • Damaged forward clutch piston
    • Missing forward clutch piston inner and outer seals
    • Cut forward clutch piston inner and outer seals
    • Damaged forward clutch piston inner and outer seals
    • Missing input housing to forward clutch housing O-ring seal
    • Cut input housing to forward clutch housing O-ring seal
    • Damaged input housing to forward clutch housing O-ring seal
    • Damaged forward clutch housing
    • Damaged forward clutch housing retainer and ball assembly
    • Forward clutch housing retainer and ball assembly is not sealing.

Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

12

Inspect the 3-4 clutch assembly for the following conditions:

    • Worn clutch plates
    • Porosity in the 3-4 clutch piston
    • Damaged 3-4 clutch piston
    • Missing 3-4 clutch inner and outer seals
    • Cut 3-4 clutch inner and outer seals
    • Damaged 3-4 clutch inner and outer seals
    • Damaged 3-4 clutch spring assembly
    • Damaged 3-4 clutch apply ring
    • Damaged piston seal grooves
    • Plugged orifice cup plug
    • Missing orifice cup plug

Refer to Transmission Overhaul in the 4L60-E section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Intermittent Conditions in Engine Controls

13
  1. Change the AT fluid and filter.
  2. Inspect for correct transmission fluid level.

    3. Refer to Transmission Fluid Check .

  3. Add new AT fluid as necessary.

    4. Important: The Clear TAPS function will clear all adapt cells. This may affect transmission performance. The PCM will update the transmission adapt cell values as the vehicle is driven.

  4. Using the Scan Tool , perform the Clear TAPS function.

Did you complete the above procedure?

--

Go to Step 14

--

14

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
    4. • Drive the vehicle in D4, with the TCC ON, and a throttle position of 20-99%.
    • Ensure that the Scan Tool TCC Slip Speed is -20 to +50 RPM for at least 7 seconds.
  4. Select Specific DTC.
  5. Enter DTC P1870.

Has the test run and passed?

--

System OK

Go to Step 1