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 MANUALSGMC2011SAVANA SPECIAL 4.8 AREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 4 (ENGINE CONTROLS AND FUEL - 6.6L (LGH) - DTC P0016 THROUGH DTC P11DC)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0420TESTINGCIRCUIT/SYSTEM TESTING
2011 GMC Savana Special 4.8 A
Circuit/System Testing
2011 GMC Savana Special 4.8 ASECTION Circuit/System Testing
WARNING: This page is about a different variant/trim than selected.
- Verify the following conditions do not exist with the exhaust system:
- Exhaust leaks before or after the diesel oxidation catalyst. Refer to Exhaust Leakage for further diagnosis.
- Physical damage
- Loose or missing hardware
- If a condition is found, repair or replace the affected exhaust system components as necessary.
- Verify the following conditions do not exist with the diesel oxidation catalyst:
- Physical damage or alterations
- Internal rattles caused by a damaged catalyst substrate
- Restrictions
- If a condition is found, replace the diesel oxidation catalyst.
- Observe the scan tool Freeze Frame/Failure Records data for DTC P0420. Determine the temperature difference between EGT Sensor 1 and 2 and between EGT Sensor 2 and 4.
- If EGT Sensor 4 is greater than EGT Sensor 2 by at least 100°C (180° F) and EGT Sensor 2 is within 100°C (180° F) of EGT Sensor 1, replace the diesel oxidation catalyst.
- Test the Q57 Indirect fuel injector flow. Refer to Indirect Fuel Injector Diagnosis
. Verify the flow amount is at least 17 ml.
- If not within the specified range, replace the Q57 Indirect fuel injector.
- Verify the following conditions do not exist:
- Off road fuel or red dye fuel
- Low quality B-20 fuel
- Fuel containing high sulfur content
- Engine oil or coolant consumption
- If a condition is found, repair as necessary.
- If all components test normal and no conditions are found, operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
- If the DTC sets, refer to Circuit/System Testing - step 1 above.
NOTE:
In cold climates diesel fuel may gel in the indirect fuel injector system. This may prevent the injector from operating normally and may cause the DTC to set.
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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.