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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 59 (Automatic Transmission Diagnosis - 4L80-E) >> Diagnostic Tests >> DTC P1870: Transmission Component Slipping >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Perform the transmission fluid checking procedure. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Was the fluid checking procedure performed? If so, go to next step. If not, see appropriate AUTOMATIC article in TRANSMISSION SERVICING.
  3. Install a scan tool. Turn ignition on, engine off. Before clearing the DTCs, use the scan tool to record the freeze frame and failure records. Using the CLEAR INFO function erases the freeze frame and failure records from the PCM. Record the freeze frame and failure records. Clear the DTCs. With the engine idling and at normal operating temperature, apply the brake pedal. Select each transmission range. See TFP MANUAL VALVE POSITION SWITCH LOGIC  table under DESCRIPTION & OPERATION. Does each selected transmission range match the scan tool TFP SWITCH A/B/C display? If so, go to next step. If not, see DTC P1810: TFP MANUAL VALVE POSITION SWITCH ASSEMBLY - CIRCUIT MALFUNCTION .
  4. Drive the vehicle under the following conditions:
    • The transmission fluid temperature is 50-266°F (20-130°C).
    • The transmission is in D4.
    • The TCC duty cycle is greater than 80 percent.
    • The throttle angle is 10-80 percent.

    At any time, is the TCC slip speed greater than 120 RPM for 10 seconds? If so, go to next step. If not, see DIAGNOSTIC AIDS .

  5. Drive the vehicle under the following conditions:
    • The transmission is in D3.
    • Command the TCC on with the scan tool.
    • The throttle angle is 10-80 percent.

    At any time, is the TCC slip speed greater than 120 RPM for 10 seconds? If so, go to step  7. If not, go to next step.

  6. Repeat the procedure in step  4. Drive the vehicle under the following conditions:
    • The transmission is in D4.
    • The TCC duty cycle is greater than 80 percent.
    • The throttle angle is 10-80 percent.

    Is the TCC slip speed greater than 120 RPM? If so, go to step  8. If not, go to step  11.

  7. See SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING. Did you find and correct the condition? If so, go to step  12.
  8. Perform the line pressure check procedure. See HYDRAULIC PRESSURE TESTS  under PERFORMANCE TESTS. Is the line pressure within specifications? If so, go to next step. If not, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.
  9. Remove the transmission oil pan. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Inspect for contaminated fluid and excessive material in the pan. Is the fluid or the pan contaminated? If so, see appropriate OVERHAUL article. If not, go to next step.
  10. Inspect the 1-2 shift solenoid valve for contamination or damaged seals. Inspect the 2-3 shift solenoid valve for contamination or damaged seals. Did you find and correct the condition? If so, go to step  12. If not, go to next step.
  11. Inspect the following components for contamination or sticking:
    • 2-3 Shift Valve
    • 3-4 Shift Valve

    Did you find and correct the condition? If so, go to next step. If not, see appropriate OVERHAUL article.

  12. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Operate the vehicle.
    • Ensure that transmission fluid temperature is 50-266°F (20-130°C).
    • Drive the vehicle in 4th gear, with the TCC commanded on.
    • The throttle angle is 10-100 percent.
    • The PCM must see a slip of -20 to 20 RPM for greater than 10 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P1870.

    Has the test run and passed? If so, system is okay. If not, go to step  1.

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