LEMON Manuals: Even more car manuals for everyone
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 P0730: Incorrect Gear Ratio >> 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 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. See TFP MANUAL VALVE POSITION SWITCH LOGIC  table under DESCRIPTION & OPERATION. Does the scan tool TFP SWITCH A/B/C display match each selected gear range? If so, go to next step. If not, see DTC P1810: TFP MANUAL VALVE POSITION SWITCH ASSEMBLY - CIRCUIT MALFUNCTION .
  4. Drive the vehicle in D3 with greater than 15 percent throttle angle. Drive the vehicle above 7 MPH for greater than 2 seconds in each specified gear range. Use the scan tool snapshot mode to record the transmission gear ratio for each commanded gear range: Reverse, 1st, 2nd, and 3rd. Are the commanded gear ratios within the values for each specified gear range? See GEAR RATIO SPECIFICATIONS  table. If so, see DIAGNOSTIC AIDS . If not, go to next step.
  5. Connect the Pressure Gauge (J-21867) to the transmission line pressure tap. 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. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Engine is running.
    • Drive the vehicle in Reverse, 1st, 2nd, and 3rd gear. The PCM must see a valid gear ratio range versus the commanded gear ratio.
    • Select SPECIFIC DTC.
    • Enter DTC P0730.

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

scientia non olet · About LEMON Manuals