Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 341 (STARTING SYSTEM)DIAGNOSTIC INFORMATIONDTC P0560TESTING
1999 GMC Forward Control 5.7 R, Automatic
DTC P0560: Testing
1999 GMC Forward Control 5.7 R, AutomaticSECTION Testing
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
- Did you perform the DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL? If so, go to next step. If not, go to DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL .
- Install a scan tool. Start the engine. Increase engine speed above 1,500 RPM. With a scan tool, observe the IGNITION 1 SIGNAL parameter in the PCM data list. Does the scan tool indicate that the Ignition 1 Signal parameter is greater than the specified range of 11.0V? If so, go to step 6. If not, go to next step.
- Compare the battery voltage at the battery with the ignition 1 signal parameter in the PCM data list. Is the battery voltage and PCM ignition 1 readings different by more than the value specified of 0.7V? If so, go to next step. If not, go to TEST A: CHARGING SYSTEM TEST in GENERATORS & REGULATORS article under ELECTRICAL.
- Test the battery positive voltage circuit of the PCM for a high resistance. Did you find and correct the condition? If so, go to step 7. If not, go to next step.
- Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If so, go to step 7. If not, go to next step.
- Replace the PCM. See POWERTRAIN CONTROL MODULE in REMOVAL & INSTALLATION article under ENGINE PERFORMANCE. After replacement is complete, go to next step.
- Review and record the scan tool Fail Records data. Use the scan tool in order to clear the DTC. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. See CONDITIONS FOR RUNNING THE DTC . Using the scan tool, observe the SPECIFIC DTC INFORMATION for DTC P0560 until the test runs. Does the scan tool indicate that DTC P0560 failed this ignition? If so, go to step 2. If not, then system is okay.
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When to See a Mechanic
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.