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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) >> Symptom Tests >> Tow/Haul Switch/Indicator Always On Or Inoperative >> 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. Install a scan tool. Turn ignition on, engine off. Cycle the tow/haul switch while observing TOW/HAUL MODE on the scan tool. Does the scan tool display ACTIVE when the switch is first pressed, and then INACTIVE when the switch is pressed again? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  2. Disconnect the instrument panel wiring harness connector C201B from the tow/haul switch. Install a fused jumper wire from instrument panel wiring harness connector C201B terminal B5 to terminal B2. Does the scan tool TOW/HAUL MODE indicate a status change? If so, go to step  13. If not, go to next step.
  3. Using a DVOM and the Connector Test Adapter Kit (J-35616-A), measure the voltage at instrument panel wiring harness connector C201B terminal B5. Is ignition voltage measured? If so, go to step  5. If not, go to next step.
  4. Measure the voltage at BCM harness connector C1 terminal B12. Is ignition voltage measured? If so, go to step  8. If not, go to step  14.
  5. Install a fused jumper wire between the instrument panel wiring harness connector C201B terminals B5 and B2. Measure for voltage at body wiring harness junction block connector C2 terminal C9. Is ignition voltage measured? If so, go to next step. If not, go to step  9.
  6. Measure for voltage at body wiring harness junction block connector C1 terminal F2. Is ignition voltage measured? If so, go to next step. If not, go to step  12.
  7. Measure for voltage at splice pack 203 (SP203) terminal "E". Is ignition voltage measured? If so, go to step  11. If not, go to step  10.
  8. Test the tow/haul switch signal circuit (553) of the tow/haul switch for an open or shorted condition. Did you find and correct the condition? If so, go to step  15. If not, see DIAGNOSTIC AIDS .
  9. Test the ground circuit (1850) of the tow/haul switch for an open or shorted condition between instrument panel wiring harness connector C201B terminal B2 and body wiring harness junction block connector C2 terminal C9. Did you find and correct the condition? If so, go to step  15. If not, see DIAGNOSTIC AIDS .
  10. Test the ground circuit (1850) of the tow/haul switch for an open or shorted condition between the body wiring harness junction block connector C1 terminal F2 and splice pack 203 terminal "E". Did you find and correct the condition? If so, go to step  15. If not, see DIAGNOSTIC AIDS .
  11. Repair splice pack 203. Did you complete the repair? If so, go to step  15.
  12. Replace the body wiring harness junction block. Did you complete the replacement? If so, go to step  15.
  13. Replace the tow/haul switch. See SHIFT LEVER REPLACEMENT - ON VEHICLE WITH TOW/HAUL SWITCH  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  15.
  14. Test the BCM for proper operation. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. Did you find and correct the condition? If so, go to next step.
  15. After the repair is complete, observe TOW/HAUL MODE on the scan tool display, while cycling the tow/haul switch. Does the scan tool display ACTIVE when the switch is first pressed, and then INACTIVE when the switch is pressed again? If so, system is okay. If not, go to step  1.
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