Symptoms Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Cuts Out/Misses, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, Fuel Knock/Combustion Noise, or Surges/Chuggles Excessive Smoke (Black), Excessive Smoke (White), Excessive Smoke (Gray or Blue).

Test Procedure

Test for the following conditions:
- The sensor systems for the following:
  - Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage.
  - Idle the engine and observe the Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure parameters. If the pressure difference is more than 2 MPa, a fuel control issue may exist.
  - Inspect for the EGR valve sticking open. Command the valve to 20%. Desired and actual position should not be more than 3% different.
  - Inspect the 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.
  - Inspect the engine coolant temperature (ECT) sensor. Use the scan tool in order 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 for an intermittent FRP sensor signal by wiggling the harness between the sensor and the ECM with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool.
  - Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Testing for Intermittent Conditions and Poor Connections .
- The Air Induction System for the following:
  - Leaks in the Induction system before the Turbocharger. Refer to Induction System Smoke Test in Charge Air Cooler Diagnosis (Induction System Smoke Test) , Charge Air Cooler Diagnosis (Full System Air Leak Test) or Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test) .
  - Leaks in the Charge Air Cooler system. Refer to Charge Air Cooler Air Leak Test in Charge Air Cooler Diagnosis (Induction System Smoke Test) , Charge Air Cooler Diagnosis (Full System Air Leak Test) or Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test) .
  - Leaks in the engine assembly. Refer to Full System Air Leak Test in Charge Air Cooler Diagnosis (Induction System Smoke Test) , Charge Air Cooler Diagnosis (Full System Air Leak Test) or Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test) .
- The Fuel System for the following:
  - Inspect the fuel quality. Refer to Contaminants-in-Fuel Diagnosis and Fuel System Specifications .
  - Inspect the fuel pressure regulator voltage supply circuit for an intermittent short to ground. Observe the FRP regulator command percent while cranking. A range of 85-95 percent indicates a possible short to ground condition.
  - Inspect the fuel pressure regulator voltage supply circuit for a short to voltage.
  - Inspect the fuel supply to the fuel injection pump. Refer to Fuel System Diagnosis .
  - Inspect the fuel system for a plugged fuel filter, high vacuum, air in the fuel system, etc. 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 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 supply system vacuum while the problem exists. Refer to Fuel System Diagnosis .
  - Inspect the engine speed signal circuit for high resistance.
  - If the ECM or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to Fuel Injector Flow Rate Programming .
  - Inspect for restricted or plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .
  - Inspect for a sticking Fuel Pressure Regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above Desired Idle Speed to 50 RPM below Desired Idle Speed. Refer to Fuel Pressure Regulator Diagnosis .
  - Inspect the fuel tank cap vent for proper operation.
- Engine mechanical for the following.
  - 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 .
  - Excessive oil in the combustion chamber-Leaking valve seals-Refer to Oil Consumption Diagnosis .
If the above conditions do not address the symptom, refer to Additional Symptoms Tests .