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Home >> GMC >> 1998 >> Yukon RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 70 (Automatic Transmission Diagnosis - 4L80-E (Gasoline)) >> Diagnostic Tests >> DTC P0502: Output Shaft Speed (OSS) Sensor Circuit Low Input >> Diagnostic Procedures

Diagnostic Procedures

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  1. Connect scan tool to DLC. Turn ignition switch to ON position. DO NOT start engine. Using scan tool, record freeze frame and failure records for reference. Data will be lost when DTCs are cleared later in this test.
  2. Raise and support vehicle. Start engine and let idle. Apply brake pedal. Shift gear selector to any forward gear position. Select "Output Speed" on scan tool. With drive wheels rotating, if transmission output speed does not increase when wheel speed increases, go to next step. If transmission output speed increases when wheel speed increases, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect OSS sensor connector. Turn ignition on. Using a DVOM set to DC volts, measure voltage between ground and sensor high circuit at OSS sensor connector. See procedures in WIRING DIAGRAMS . If voltage is 4.0-5.1 volts, go to next step. If voltage is not 4.0-5.1 volts, go to step 5).
  4. With ignition on, measure voltage between ground and sensor low circuit at OSS sensor connector. See WIRING DIAGRAMS . If voltage is less than .2 volt, go to step 7). If voltage is more than .2 volt, check for short to voltage or wires shorted together in OSS sensor circuits. Repair as necessary, then go to step 12). If circuits are okay, check VCM and connector terminals for corrosion or poor tension. Repair as necessary, then go to step 12). If VCM and connector terminals are okay, replace VCM, then go to step 12).
  5. If voltage in step 3) was less than 4.0 volts, go to next step. If voltage in step 3) was more than 5.1 volts, check for short to voltage or wires shorted together in OSS sensor circuits. Repair as necessary, then go to step 12). If circuits are okay, check VCM and connector terminals for corrosion or poor tension. Repair as necessary, then go to step 12). If VCM and connector terminals are okay, replace VCM, then go to step 12).
  6. Check for high resistance or open in OSS sensor high circuit. On 4WD models, an in-line connector is located between engine harness and OSS sensor harness at transfer case. Repair as necessary, then go to step 12). If circuit is okay, check for short to ground in OSS sensor high circuit. Repair as necessary, then go to step 12). If circuit is okay, go to step 10).
  7. With ignition on, measure voltage between OSS sensor connector terminals. If voltage is 4.0-5.1 volts, go to step 9). If voltage is not 4.0-5.1 volts, go to next step.
  8. Check for open in OSS sensor low circuit between connector and VCM. On 4WD models, an in-line connector is located between engine harness and OSS sensor harness at transfer case. Repair as necessary, then go to step 12). If circuit is okay, go to step 10).
  9. Using a DVOM, measure resistance between OSS sensor terminals. If resistance is not 1042-2088 ohms, replace OSS sensor, then go to step 12). If resistance is 1042-2088 ohms, shift transmission into Neutral. Select AC volts on DVOM. Rotate rear wheels and note voltage. If voltage is more than .5 volt, go to next step. If voltage is less than .5 volt, go to step 11).
  10. Turn ignition off. Reconnect OSS sensor connector. Disconnect appropriate VCM connector for OSS sensor circuits. Connect a DVOM set to AC volts, to OSS sensor circuits at VCM connector. See WIRING DIAGRAMS . Rotate rear wheels and measure voltage. If voltage is more than .5 volt, check VCM and connector terminals for corrosion or poor tension. Repair as necessary, then go to step 12). If VCM and connector terminals are okay, replace VCM, then go to step 12).
  11. Remove OSS sensor from transmission. Inspect OSS sensor rotor for damage or misalignment. Repair as necessary, then go to next step. If sensor rotor is okay, replace OSS sensor, then go to next step.
  12. After repair is complete, select DTC on scan tool. Select "Clear Info" function. Select "Specific DTC" and enter DTC "P0502". Test drive vehicle. Ensure transmission output speed is more than 500 RPM for one second. If DTC P0502 is not present, repair is complete. If DTC P0502 is still present, repeat test.
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