GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Hard Start

Inspection

Action

DEFINITION: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately dies.

Preliminary Inspection
    • Refer to Symptoms - Engine Controls .
    • Ensure the driver is using the correct starting procedure.

Sensor Inspection
    • Inspect the engine coolant temperature (ECT) sensor. Use the scan tool to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
    • Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.

Fuel System Inspection
    • Inspect the quality of the Fuel. Refer to Contaminants-in-Fuel Diagnosis and Fuel System Specifications .
    • Inspect the fuel pressure regulator 12-volt circuit for an intermittent short to ground. Observe the FRP Command percent while cranking. A range of 85-95 percent indicates a possible short to ground condition.
    • Inspect the fuel supply to the fuel injection pump. Refer to Fuel System Diagnosis .
    • Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Inspect for air in the fuel system. Refer to Fuel System Diagnosis .
    • Inspect for external fuel leaks. Refer to Fuel Leak Diagnosis .
    • Inspect for high engine oil level. Refer to Fuel in Engine Oil .
    • Inspect for low fuel pressure. Command the fuel pressure to 180 MPa with a scan tool while the engine is at idle. If 180 MPa is not achieved, perform Fuel System Diagnosis - High Pressure Side .
    • Inspect the fuel tank cap vent for proper operation.

Electrical System Inspection

Inspect for a slow cranking speed. Refer to Symptoms - Engine Electrical .

Air Intake System Inspection
    • Inspect the air cleaner and air intake ducts for a restrictions or leaks.
    • Inspect for a restriction in turbocharger inlet duct.
    • Inspect for a restriction or a leak in the intake manifolds.

Exhaust System Inspection

Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust .

Engine Mechanical Inspection

Inspect the engine for the following conditions:

    • Improper valve timing
    • Bent pushrods
    • Worn rocker arms--Refer to Valve Rocker Arm and Shaft Cleaning and Inspection .
    • Low engine compression--Refer to Engine Compression Test .
    • Broken or weak valve springs
    • Worn camshaft lobes--Refer to Camshaft and Bearings Cleaning and Inspection .

Additional Inspection
    • Inspect for an intermittent CKP signal. Refer to Testing for Intermittent Conditions and Poor Connections .
    • Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
    • Inspect the Service Bulletins for control module software updates.