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Home >> GMC >> 1998 >> Yukon 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 70 (Automatic Transmission Diagnosis - 4L80-E (Gasoline)) >> Diagnostic Tests >> DTC P0503: Output Shaft Speed (OSS) Sensor Circuit Intermittent >> 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. Select "Transmission OSS" on scan tool. Shift gear selector into "D3". With drive wheels rotating, slowly accelerate vehicle to 2000 RPM and hold steady. If transmission output speed drops or fluctuates more than 1000 RPM, go to next step. If transmission output speed does not drop or fluctuate more than 1000 RPM, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect OSS sensor connector. Connect a DVOM set to AC volts to OSS sensor terminals. Start engine and shift gear selector into "D3". With drive wheels rotating, slowly accelerate vehicle to 2000 RPM and hold steady. If DVOM voltage drops or fluctuates at 2000 RPM, go to step 10). If DVOM voltage does not drop or fluctuate at 2000 RPM, go to next step.
  4. Turn ignition off. Connect a DVOM set to DC volts between ground and sensor high circuit at OSS sensor connector. See procedures in WIRING DIAGRAMS . Turn ignition on. If voltage is 4.0-5.1 volts and steady, go to next step. If voltage is not 4.0-5.1 volts and steady, go to step 6).
  5. 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 8). 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 13). If circuits are okay, check VCM and connector terminals for corrosion or poor tension. Repair as necessary, then go to step 13). If VCM and connector terminals are okay, replace VCM, then go to step 13)
  6. If voltage in step 4) was less than 4.0 volts, go to next step. If voltage in step 4) 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 13). If circuits are okay, check VCM and connector terminals for corrosion or poor tension. Repair as necessary, then go to step 13). If VCM and connector terminals are okay, replace VCM, then go to step 13).
  7. Check for high resistance or open in OSS sensor high circuit. Repair as necessary, then go to step 13). If circuit is okay, check for short to ground in OSS sensor high circuit. Repair as necessary, then go to step 13). If circuit is okay, go to step 11).
  8. With ignition on, measure voltage between OSS sensor connector terminals. If voltage is 4.0-5.1 volts and steady, go to step 11). If voltage is not 4.0-5.1 volts and steady, go to next step.
  9. Check for high resistance or open in OSS sensor low circuit between connector and VCM. Repair as necessary, then go to step 13).
  10. Using a DVOM, measure resistance between OSS sensor terminals. If resistance is not 1042-2088 ohms, replace OSS sensor, then go to step 13). If resistance is 1042-2088 ohms, go to step 12).
  11. 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 13). If VCM and connector terminals are okay, replace VCM, then go to step 13).
  12. Remove OSS sensor from transmission. Inspect OSS sensor rotor for looseness, damage or misalignment. Repair as necessary, then go to next step. If sensor rotor is okay, replace OSS sensor, then go to next step.
  13. After repair is complete, select DTC on scan tool. Select "Clear Info" function. Select "Specific DTC" and enter DTC "P0503". Test drive vehicle. Ensure transmission output speed is more than 500 RPM with no RPM change more than 450 RPM for one second. If DTC P0503 is not present, repair is complete. If DTC P0503 is still present, repeat test.
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