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Home >> Cadillac >> 2003 >> Seville SLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P1635: 5-Volt Reference 1 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Observe the Freeze Frame/Failure Records for this DTC. Turn off the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Turn ignition off. Disconnect Exhaust Gas Recirculation (EGR) valve. Turn ignition on, with engine off. Command the EGR valve to 100 percent with a scan tool. Measure the voltage between the EGR valve 5-volt reference circuit and a good ground. Is the voltage 4.8-5.2 volts? If yes, go to step  5. If no, go to next step.
  4. Is the voltage more than 5.2 volts? If yes, go to step  8. If no, go to step  6.
  5. Connect the EGR valve. Disconnect the Manifold Absolute Pressure (MAP) sensor. Command the EGR valve to 100 percent with a scan tool. Measure the voltage between the MAP sensor 5-volt reference circuit and a good ground. Is the voltage 4.8-5.2 volts? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step. 10.
  6. Monitor the DVOM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. If the voltage changes when one of the devices is disconnected, replace that component.

    Did you replace a component? If yes, go to step  12. If no, go to next step.

  7. Turn ignition off. Disconnect the PCM. Test the 5-volt reference circuits for a short to ground or to any sensor low reference circuit. Did you find and correct the condition? If yes, go to step  12. If no, go to step  11.
  8. Test all the 5-volt reference circuits and the MAP sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  9. Test for a short between the EGR 5-volt reference circuit and the EGR solenoid control high circuit. Did you find and correct the condition? If yes, go to step  12. If no, go to step  11.
  10. Replace the EGR valve. See EGR VALVE under EMISSION SYSTEMS & SUB-SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  12.
  11. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to next step.
  12. Clear the DTCs with a scan tool. Turn off the ignition for 30 seconds. Start the engine and operate vehicle within the Conditions For Running DTC. You may also operate vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to step  2. If no, go to next step.
  13. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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