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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 69 (Automatic Transmission Diagnosis - 4L80-E (Diesel)) >> Diagnostic Tests >> DTC P0730: Incorrect Gear Ratio >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Cab & Chassis Sierra and 2002 Chevrolet Cab & Chassis 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 failure records. Using the CLEAR INFO function erases the failure records from the PCM. Record the DTC failure records. Clear the DTCs. Start the engine. Select TFP SWITCH A/B/C on scan tool. Apply the parking brake, and select each transmission range. Does the scan tool TFP SWITCH A/B/C display match each selected gear range? See TFP MANUAL VALVE POSITION SWITCH LOGIC  table under DESCRIPTION & OPERATION. If so, go to next step. If not, see DTC P1810: TFP MANUAL VALVE POSITION SWITCH ASSEMBLY - CIRCUIT MALFUNCTION  .
  4. Drive the vehicle in Reverse and "D4". Hold the vehicle speed above 5 MPH for greater than 2 seconds in the specified gear range. Use the scan tool snapshot mode to record the transmission gear ratio for each commanded gear range: Reverse, 1st, 2nd, 3rd and 4th. Are the gear ratios within the parameters for each specified gear range? See GEAR RATIO SPECIFICATIONS  table. If so, see DIAGNOSTIC AIDS  . If not, go to next step.
  5. Perform the line pressure check procedure. See HYDRAULIC PRESSURE TESTS  under PERFORMANCE TESTS. Is the line pressure within specifications for each selected gear range? If so, go to next step. If not, go to step  8 .
  6. Remove the transmission oil pan. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Inspect the oil pan and the fluid for contamination. Was excessive contamination found? If so, see appropriate OVERHAUL article. If not, go to next step.
  7. Inspect the transmission for the following conditions:
    • Sticking shift valves.
    • Stuck apply pistons.

    Did you find and correct the condition? If so, go to step  10 . If not, see appropriate OVERHAUL article.

  8. Is the system line pressure low only in the specific gear which indicated an incorrect gear ratio? If so, go to next step. If not, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.
  9. Inspect for fluid pressure loss in the following areas:
    • 1-2 Shift Solenoid Valve Seal
    • 2-3 Shift Solenoid Valve Seal
    • Valve Body Passages
    • Valve Body Gaskets
    • Band Apply Pistons And Seals
    • Clutch Apply Pistons And Seals

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

    10. NOTE: 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.
  10. Change the ATF and filter. Inspect for correct fluid level. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Using the scan tool, perform the CLEAR TAPS function. Did you complete the above procedure? If so, go to next step.
  11. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Engine is running.
    • Drive the vehicle in Reverse, 1st, 2nd, 3rd and 4th gear. The PCM must see a valid gear ratio range versus the commanded gear ratio for 7 seconds.
    • Select SPECIFIC DTC.
    • Enter DTC P0730.

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

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