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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 109 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0502: VSS Circuit - Low Input (A/T) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine. Using scan tool, monitor OSS. Drive vehicle at more than 3 MPH. If reading is not consistently less than 100 RPM, problem is intermittent. See DIAGNOSTIC AIDS  . If reading is consistently less than 100 RPM, go to next step.
  2. Turn ignition off. Disconnect PCM harness connectors J1 and J2. Using a DVOM, check resistance between PCM harness connector J2 terminals No. 42 (Purple wire) and No. 62 (Yellow wire). If resistance reading is 1530-1870 ohms, go to next step. If resistance reading is less than 1530 ohms, go to step  4 . If resistance reading is more than 1870 ohms, go to step  5 .
  3. Disconnect OSS harness connector. Check for continuity between ground and OSS harness connector terminal "B" (Yellow wire). If continuity exists, repair short to ground in Yellow wire circuit. If continuity does not exist, check sensor for correct torque and check connector at PCM. If sensor is tight and connector is okay, replace PCM.
  4. Disconnect OSS harness connector. Check for continuity between transaxle output shaft speed sensor harness connector terminals "A" (Purple wire) and "B" (Yellow wire). If continuity exists, repair short between Purple wire and Yellow wire circuits. If continuity does not exist, replace sensor.
  5. Disconnect OSS harness connector. Check for open in Purple wire and Yellow wire between OSS and PCM. If continuity exists in both circuits, check for loose connection in connectors. Repair as necessary. If terminals are okay, replace OSS. If continuity does not exist in both circuits, repair open in Purple wire or Yellow wire circuit.
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