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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 260 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0340: CAMSHAFT POSITION SENSOR CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
  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. Connect a scan tool. Attempt to start the engine. Observe the DTC information with a scan tool. Are DTCs P0335, P0340, and P0385 set? If yes, go to step  8. If no, go to next step.
  3. Start the engine. Observe the CMP SENSOR RPM parameter with a scan tool. Does the scan tool parameter indicate RPM? If yes, go to next step. If no, go to step  5.
  4. 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? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Turn ignition off. Disconnect the CMP sensor. Turn ignition on, with engine off. Probe the CMP sensor 12-volt reference circuit with a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  12.
  6. Turn ignition off. Jumper the CMP circuits from the CMP sensor to the CMP sensor harness connector. Turn ignition on, with engine off. Measure the voltage drop from the CMP sensor low reference circuit to a good ground. Is the voltage more than 0.2 volts? If yes, go to step  13. If no, go to next step.
  7. Turn ignition off. Remove the jumpers from the CMP circuits. Turn ignition on, with engine off. Observe the CMP SENSOR RPM parameter with a scan tool. Momentarily and repeatedly probe the CMP sensor signal circuit with a test light that is connected to battery voltage. Does the CMP sensor RPM change when the test light contacts the signal circuit? If yes, go to step  15. If no, go to step  14.
  8. Disconnect the CMP sensor. Observe the 12-VOLT REFERENCE parameter with a scan tool. Does the 12-volt reference display OK? If yes, go to step  17. If no, go to next step.
  9. Raise and support vehicle. Disconnect the CKP "A" sensor. Observe the 12-VOLT REFERENCE parameter with a scan tool. Does the 12-volt reference display OK? If yes, go to step  18. If no, go to next step.
  10. Disconnect the CKP "B" sensor. Observe the 12-VOLT REFERENCE parameter with a scan tool. Does the 12-volt reference display OK? If yes, go to step  19. If no, go to next step.
  11. Test the 12-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  12. Test the 12-volt reference circuit for an open or a high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  13. Test the low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  14. Test the high resolution signal circuit for a open, short to ground, or a short to voltage. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  15. Test for an intermittent and/or poor connections at the CMP sensor. Did you find and correct the condition? If yes, go to step  21. If no, go to step  17.
  16. Test for an intermittent and/or poor connections at the PCM. Did you find and correct the condition? If yes, go to step  21. If no, go to  20.
  17. Replace the CMP sensor. See CAMSHAFT POSITION SENSOR under SENSORS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  18. Replace the CKP "A" sensor. See CRANKSHAFT POSITION SENSOR under SENSORS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  19. Replace the CKP "B" sensor. See CRANKSHAFT POSITION SENSOR under SENSORS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  20. 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.
  21. 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.
  22. 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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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.