Engine Controls - 6.6l (Troubleshooting & Diagnosis) — Chevrolet Cab & Chassis Silverado 3500 (2004-2007)

Important Preliminary Inspections Before Starting

Before using this section, perform the Diagnostic System Check - Vehicle in Vehicle DTC Information and verify all of the following conditions

The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
Diagnostic trouble codes (DTCs) are not stored.
The scan tool data is within the normal operating range. Refer to «Scan Tool Data List»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-diagnostic-information-procedures__scan-tool-data-list) .
Verify the customer concern and locate the correct symptom. Inspect the items indicated under that symptom.
Several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely important, and can lead to correcting a condition without further inspections and can save valuable time.
Verify the proper installation of any of the following non-original equipment accessories: Lights Cellular phone Remote starter system Non-factory installed alarm

Visual and Physical Inspection

Inspect the following items

The control module grounds for being clean, tight, and in their proper location.
The vacuum hoses for splits, kinks, and proper connections, as shown on the Vehicle Emission Control Information label.
The wiring for the following items: Proper connections Pinches Cuts
Inspect for the installation of any Power Enhancing Devices. It may be necessary to remove these items for proper diagnosis.
The following symptom tables contain groups of possible causes for each symptom. The order of these procedures is not important. If the scan tool readings do not indicate the problems, then proceed in a logical order, easiest to inspect or most likely to cause first. In order to determine if a specific vehicle is using a particular system or component, refer to «Engine Controls Schematics»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) for an application.

Verify Customer's Concern

Locate the correct symptom table. Inspect the items indicated under that symptom from the following symptom tables

«Intermittent Conditions»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__intermittent-conditions)
«Hard Start»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__hard-start)
«Surges/Chuggles»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__surgeschuggles)
«Lack of Power, Sluggishness, or Sponginess»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__lack-of-power-sluggishness-or-sponginess)
«Fuel Knock/Combustion Noise»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__fuel-knockcombustion-noise)
«Hesitation, Sag, Stumble»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__hesitation-sag-stumble)
«Cuts Out, Misses»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__cuts-out-misses)
«Poor Fuel Economy»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__poor-fuel-economy)
«Rough, Unstable, or Incorrect Idle and Stalling»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__rough-unstable-or-incorrect-idle-and)
«Excessive Smoke (Gray or Blue)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__excessive-smoke-gray-or-blue) or «Excessive Smoke (White)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__excessive-smoke-white) or «Excessive Smoke (Black)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis__excessive-smoke-black)

Intermittent Conditions

Inspections	Action
DEFINITION: The condition is not currently present but is indicated in DTC history. OR There is a customer concern, but the symptom cannot currently be duplicated, if the condition is not DTC related.
Preliminary	Refer to Important Preliminary Inspection Before Starting in Symptoms - Engine Controls . The fault must be present to locate a problem using the DTC table. If a fault is intermittent, the use of DTC tables may result in the replacement of good parts.
Visual/Physical	This step is an important aid for locating a condition without extensive testing. Perform a thorough visual and physical inspection of the following components: Wiring harness for damage or cuts A misrouted harness that is too close to high voltage or high current devices such as the following: Motors Generators Vacuum hoses for the following conditions: Proper routing Proper connections Splits in the hose or the connections Kinks The control module and body grounds are clean and tight. Battery connections are clean and tight. Charging system for proper operation-Refer to Charging System Test in Engine Electrical.
Harness/Connector Test	Many intermittent open or shorted circuits come and go with harness and connector movement caused by vibration, engine torque, bumps and rough pavement, etc. Test for this type of condition by performing the applicable procedure from the following list: Move the related connectors and wiring while monitoring the appropriate scan tool data. Move the related connectors and wiring with the component commanded ON and OFF, with the scan tool. Observe the components operation. With the engine running, move the related connectors and wiring while monitoring engine operation. If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
Electrical Connections or Wiring	Poor electrical connections and terminal tension or wiring faults cause most intermittents. Perform a careful inspection of the suspected circuit for the following: Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body, backed-out. Inspect for improperly formed or damaged terminals. Test for incorrect terminal tension. Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body. Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits. Inspect for wires that are broken inside the insulation. Inspect the harness for pinched, cut, or rubbed through wiring. Make sure the wiring does not come in contact with hot exhaust components. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Control Module Power and Grounds	Poor power or ground connections can cause widely varying symptoms. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Inspect connections at the control module connectors, fuses, and any intermediate connections between the power source and the control module or component. A test lamp or a DMM may indicate that voltage is present, but neither tests a circuits ability to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. Refer to Power Distribution Schematics in Wiring Systems. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Make sure the ground connections are clean and tight at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component.
Temperature Sensitivity	An intermittent condition may occur only when the component is cold, or only when the component is hot. The heat that affects the circuit can be engine generated or due to a poor connection in the circuit or a high electrical load. Information from the customer may help to determine if the trouble follows a pattern that is temperature related. The Freeze Frame/Failure Records or Snapshot data may help with this type of intermittent condition, where applicable. If the intermittent is related to heat, review the data for a relationship with the following: High ambient temperatures Underhood/engine generated heat Circuit generated heat due to a poor connection, or high electrical load Higher than normal load conditions (towing, etc.) If the intermittent is related to cold, review the data for the following: Low ambient temperatures-In extremely low temperatures, ice may form in a connection or component. Inspect for water intrusion. The condition only occurs on a cold start. The condition goes away when the vehicle warms up.
Electromagnetic Interference (EMI) and Electrical Noise	Some electrical components and circuits are sensitive to electromagnetic interference (EMI) or other types of electrical noise. Inspect for the following conditions: A misrouted harness that is too close to high voltage and high current devices such as, motors, generator, etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation. Electrical system interference caused by a malfunctioning relay, control module driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating. Incorrect installation of non-factory, aftermarket, add-on accessories such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell phones, etc. Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode or resistor.
Incorrect Control Module Programming	There are only a few situations where reprogramming a control module is appropriate: A new control module is installed. Revised software/calibration files have been released for this vehicle. IMPORTANT: DO NOT reprogram the control module with the SAME software/calibration files that are already present in the control module. This is not an effective repair for any type of driveability problem. Verify that the control module contains the correct software/calibration. If incorrect programming is found, reprogram the control module with the most current software/calibration. Refer to Service Programming System (SPS) in Programming and Setup.
Duplicating Failure Conditions	If the previous tests were not successful, attempt to duplicate and/or capture the failure conditions. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Review and record the Freeze Frame/Failure Records data. Clear any DTCs with a scan tool. Turn OFF the key and wait 15 seconds. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records. The vehicle must also be operating within the Conditions For Running the DTC. Refer to Conditions for Running the DTC in the supporting text of the DTC being diagnosed. Monitor DTC status for the DTC being tested. The scan tool will indicate Ran when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed. An alternate method is to drive the vehicle with a DMM connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs may help you locate the problem.
Scan Tool Snapshot	The scan tool can be set up to take a snapshot of the parameters available via serial data. The Snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed or set up in advance to trigger when a DTC sets. An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further. Refer to the scan tool user instructions for more information on the Snapshot function.

IMPORTANT
DO NOT reprogram the control module with the SAME software/calibration files that are already present in the control module. This is not an effective repair for any type of driveability problem.

Intermittent Conditions

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. Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure (FRP) should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 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 Leaks . Inspect for high engine oil level. Refer to Fuel in Engine Oil in Engine Mechanical - 6.6L. Inspect for low fuel pressure. Command the fuel pressure to 160 MPa with a scan tool while the engine is at idle. If 160 MPa is not achieved, perform Fuel System Diagnosis - High Pressure Side . At idle observe the FRP Regulator Fuel Flow Command parameter with a scan tool. If the FRP Regulator Fuel Flow Command is more than 2700 mm 3 , perform the 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 in 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 in Engine 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 in Engine Mechanical - 6.6L. Low engine compression-Refer to Engine Compression Test in Engine Mechanical - 6.6L. Broken or weak valve springs Worn camshaft lobes-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical -6.6L.
Additional Inspection	Inspect for an intermittent CKP signal. Refer to Intermittent Conditions . 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.

Hard Start

Surges/Chuggles

Inspection	Action
DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow down with no change in the accelerator pedal.
Preliminary Inspection	Refer to Symptoms - Engine Controls . Ensure the driver understands the torque converter clutch (TCC) operation. Ensure the driver understands the A/C compressor operation. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List . Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal.
Sensor Inspection	Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the fuel rail pressure (FRP) sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and the engine control module (ECM) with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool. Observe the FRP sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor issues exists. 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 fuel supply system vacuum while the problem exists. Refer to Fuel System Diagnosis . 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 .
Additional Inspection	Inspect the fuel injection control circuits between the ECM and the fuel injection control module (FICM) for a short to a 5-volt reference circuit. Inspect the control module grounds for being clean, tight, and in their proper locations. Inspect the generator output voltage. Repair if less than 9 volts or more than 16 volts. Inspect the TCC operation.

Surges/Chuggles

Lack of Power, Sluggishness, or Sponginess

Checks	Action
DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.
Preliminary Checks	Refer to Symptoms - Engine Controls . Inspect for auxiliary fuel filters. Refer to Fuel Injection Line Routing Diagram for proper fuel filter locations. Aftermarket fuel filters may restrict fuel flow. Compare the vehicle with a similar unit. Ensure the vehicle has an actual problem. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List . Remove the air filter and check for dirt, or for air ducts being plugged or leaking. Repair or replace as necessary. Inspect for a proper transmission operation. Inspect the engine oil level and quality.
Sensor Inspection	Observe the fuel rail pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor issue exists. 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 Checks	Inspect the fuel supply to the fuel injection pump. Refer to Fuel System Diagnosis . Observe the actual vs desired fuel rail pressure with a scan tool, with the engine idling. Inspect the engine speed signal circuit for high resistance. Inspect for restricted or plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Exhaust System Checks	Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust in Engine Exhaust.
Air Intake System Checks	Inspect for an air leak or restriction in the air inlet ducts or the intake manifold. Refer to DTC P0234 . Inspect for an air leak or restriction in the charge air cooler with a J 46091 Charge Air Cooler Tester. Inspect for a worn or damaged turbo charger turbine wheel, shaft or compressor wheel. Inspect for a skewed mass air flow (MAF) sensor. Refer to Diagnostic Aids in DTC P0101 .
Engine Mechanical Check	Inspect the engine for the following: Low compression Improper valve timing Improper or worn camshaft Refer to Engine Compression Test in Engine Mechanical.
Additional Checks	Inspect the control module grounds for being clean, tight, and in their proper location. Inspect the torque converter clutch (TCC) operation. Inspect the air conditioning system for proper operation. Refer to Symptoms - HVAC Systems - Automatic in HVAC Systems - Automatic or Symptoms - HVAC Systems - Manual in HVAC Systems - Manual. Inspect the generator output voltage. Refer to Charging System Test in Engine Electrical.

Lack of Power, Sluggishness, or Sponginess

Fuel Knock/Combustion Noise

Checks	Action
DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the throttle opening.
Preliminary Checks	Refer to Symptoms - Engine Controls . Ensure the vehicle has an actual problem. Inspect for smoke associated with the combustion noise. Refer to Fuel System Checks below.
Cooling System Checks	Inspect for obvious overheating problems. Refer to Engine Overheating in Engine Cooling. Inspect for a low engine coolant level. Inspect for any restricted air flow through the radiator. Refer to Radiator Cleaning in Engine Cooling. Inspect for a malfunctioning or incorrect thermostat. Inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.
Sensor Inspection	Inspect the engine coolant temperature (ECT) sensor by using 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, check for a high resistance in the coolant sensor circuit or the sensor itself. Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . 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.
Fuel System Checks	If excessive smoke is present, check for a stuck open fuel injector by performing the following procedure: Remove the ignition 1 relay. Remove the glow plugs. Refer to Glow Plug Replacement - Bank 1 and Glow Plug Replacement - Bank 2 . IMPORTANT: Do not stand in front of the glow plug holes while cranking the engine. Crank the engine while observing the glow plug holes for fuel spray. Replace the fuel injectors for the cylinders that spray fuel. Check for fuel in the oil and proper oil level. Refer to Fuel in Engine Oil in Engine Mechanical. Inspect for plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Engine Mechanical Checks	Inspect for incorrect basic engine parts such as cam, heads, pistons, etc. Inspect for any excessive oil entering combustion chamber.
Additional Checks	Review the Service Bulletins for control module software updates. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .

IMPORTANT
Do not stand in front of the glow plug holes while cranking the engine.

Fuel Knock/Combustion Noise

Hesitation, Sag, Stumble

Inspection	Action
DEFINITION: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move from a stop. If sever enough, the condition may cause the engine to stall.
Preliminary Inspection	Refer to Symptoms - Engine Controls .
Fuel System Inspection	Inspect the fuel supply system vacuum. Refer to Fuel System Diagnosis . Inspect for water contamination in the fuel. Refer to Contaminants-in-Fuel Diagnosis . Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) . Inspect for high fuel supply system vacuum after a cold start or during moderate or full throttle acceleration. If the vacuum jumps above specification, there is a restriction in the fuel system.
Sensor Inspection	Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and the engine control module (ECM) with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool. Observe the FRP sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . 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.
Additional Inspection	Review the service bulletins for control module software updates. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List . Inspect the generator output voltage. Refer to Charging System Test in Engine Electrical.

Hesitation, Sag, Stumble

Cuts Out, Misses

Inspection	Action
DEFINITION: A constant jerking that follows the engine speed, usually more pronounced as the engine load increases which is not normally felt above 1500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle, low speed, or hard acceleration for the fuel starvation that can cause the engine to cut-out.
Preliminary Inspection	Refer to Symptoms - Engine Controls . Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
Sensor Inspection	Observe the fuel rail pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. The FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor issue exists. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . 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.
Engine Mechanical Inspection	Perform the Engine Compression Test. Refer to Engine Compression Test in Engine Mechanical. Inspect the engine for the following conditions: Improper valve timing Bent pushrods Worn rocker arms Worn camshaft lobes Broken or weak valve springs, refer to Symptoms - Engine Mechanical in Engine Mechanical. Inspect the intake and exhaust manifold passages for casting flash.
Fuel System Inspection	Inspect the fuel system for a plugged fuel filter, high vacuum, air in the fuel system, etc. Refer to Fuel System Diagnosis . Inspect for water contamination in the fuel. Refer to Contaminants-in-Fuel Diagnosis . Inspect the fuel injectors for proper operation. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .

Cuts Out, Misses

Poor Fuel Economy

Inspection	Action
DEFINITION: Fuel economy, as measured by actual road tests and several tanks of fuel, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by actual road tests.
Preliminary Inspection	Refer to Symptoms - Engine Controls . Inspect the air filter for dirt or being plugged. Inspect for an air leak in the charge air cooler with a J 46091 Charge Air Cooler Tester. Inspect the air conditioning system for proper operation. Inspect the tires for correct air pressure. Inspect the driving habits of the owner. Are heavy loads being carried? Suggest to the owner to fill the fuel tank and inspect the fuel economy. Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual.
Sensor Inspection	Observe the fuel rail pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor concern exists. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . 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.
Fuel System Inspection	Inspect the fuel type and quality. Inspect the fuel system vacuum. Refer to Fuel System Diagnosis .
Cooling System Inspection	Inspect the engine coolant level. Inspect the engine thermostats for always being open or for the wrong heat range. Refer to Thermostat Diagnosis in Engine Cooling.
Additional Inspection	Inspect the transmission for proper operation. Inspect the torque converter clutch (TCC) operation. When the TCC is commanded ON, a scan tool should indicate an RPM drop. Inspect the Service Bulletins for control module software updates. Inspect the brake for proper operation.

Poor Fuel Economy

Rough, Unstable, or Incorrect Idle and Stalling

Inspection	Action
DEFINITION: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Inspection	Refer to Important Preliminary Inspection Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the vehicle for factory or aftermarket accessories that may contact the body and chassis. A grounding out condition may simulate a misfire or rough run concern. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List . Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations. Remove and inspect the air filter element for dirt or for being restricted. Refer to Air Cleaner Element Replacement . Replace as necessary.
Sensor Inspection	Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Test 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. Observe the FRP sensor and the fuel pressure regulator commanded percent at idle. The FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor issue exists. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . 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 for proper crankcase ventilation.
Fuel System Inspection	Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) . Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Contaminants-in-Fuel Diagnosis . 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 .
Engine Mechanical Inspection	Inspect engine mechanical for the following: Inspect the cylinder compression. Refer to Engine Compression Test in Engine Mechanical - 6.6L. Sticking or leaking valves Worn camshaft lobes Valve timing Bent push rods Worn rocker arms Broken valve springs Excessive oil in the combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical - 6.6L. Inspect the following components for incorrect basic engine parts: Camshaft-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical - 6.6L. Cylinder heads-Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical - 6.6L. Pistons, connecting rods, or bearings-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical - 6.6L.
Additional Inspection	Inspect the following components of the exhaust system for possible restrictions: The exhaust system for damaged or collapsed pipes The exhaust manifold for a collapsed inner wall The mufflers for heat distress or possible internal failure Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM, with little change in actual engine RPM change, indicates that EMI is present. If a problem exists, inspect routing of high voltage components, such as fuel injector wiring, near the sensor circuits. Inspect the park neutral position (PNP) switch circuit. Inspect for a short to 5 volts on one of the fuel injector control circuit between the ECM and the fuel injector control module (FICM). Inspect for faulty motor mounts. Refer to Engine Mount Inspection in Engine Mechanical - 6.6L. Inspect the intake manifold and the exhaust manifold passages for casting flash.

Rough, Unstable, or Incorrect Idle and Stalling

Excessive Smoke (Gray or Blue)

Inspection	Action
DEFINITION: Gray or blue smoke under load, idle or start up hot or cold.
Preliminary Inspections	Refer to Symptoms - Engine Controls . Ensure the customer has an actual problem. Check the coolant level in the reservoir. White coolant smoke may be mistaken for blue/gray smoke. If the coolant level is low refer to Loss of Coolant in Engine Cooling. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
Fuel System Inspection	Observe the actual vs. desired fuel rail pressure with a scan tool, with the engine running. Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Sensor Inspection	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. Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Air Intake System Inspection	Inspect the air cleaner and the air intake ducts for restriction. Inspect for contamination of the mass air flow (MAF) sensor. Inspect for a restriction in the turbocharger charged air cooler. Inspect for a restriction in the intake manifold.
Engine Mechanical Inspection	Perform a cylinder leakage test. Perform the engine compression test. Refer to Engine Compression Test in Engine Mechanical - 6.6L. Inspect for incorrect basic engine parts such as the cam, the heads, the pistons, piston rings, and valves. Inspect for excessive oil entering the combustion chamber. Refer to Oil Consumption Diagnosis in Engine Mechanical - 6.6L.
Turbocharger Inspection	Inspect for leaking seals in the turbocharger. A slight film on the intake side is normal.

Excessive Smoke (Gray or Blue)

Excessive Smoke (White)

Inspection	Action
DEFINITION: White smoke under load, idle or start up hot or cold.
Preliminary Inspection	Refer to Symptoms - Engine Controls . Ensure the customer has an actual problem. Check the coolant level in the reservoir. White coolant smoke may be mistaken for blue/gray smoke. If the coolant level is low refer to Loss of Coolant in Engine Cooling. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
Fuel System Inspection	If excessive smoke is present, inspect for a stuck open fuel injector by performing the following procedure: Remove the ignition 1 relay. Remove the glow plugs. Refer to Glow Plug Replacement - Bank 1 and Glow Plug Replacement - Bank 2 . IMPORTANT: Do not stand in front of the glow plug holes while cranking the engine. Crank the engine while observing the glow plug holes for fuel spray. Replace the fuel injectors for the cylinders that spray fuel. Inspect for contaminated oil or high oil level. Refer to Fuel in Engine Oil in Engine Mechanical - 6.6L. Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Sensor Inspection	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. Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Air Intake System Inspection	Inspect the air cleaner and the air intake ducts for restriction. Inspect for a restriction in the turbocharger charge air cooler. Inspect for a restriction in the intake manifold. Refer to Intake Manifold Cleaning and Inspection in Engine Mechanical - 6.6L.
Engine Mechanical Inspection	Inspect for incorrect basic engine parts such as the cam, the heads, the pistons, etc. Inspect for coolant entering the combustion chamber.

IMPORTANT
Do not stand in front of the glow plug holes while cranking the engine.

Excessive Smoke (White)

Excessive Smoke (Black)

Inspection	Action
DEFINITION: Black smoke under load, idle or start up hot or cold.
Preliminary Inspection	Refer to Symptoms - Engine Controls . Ensure the customer has an actual problem. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
Fuel System Inspection	Observe the actual vs. desired fuel rail pressure with a scan tool, with the engine running. Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Sensor Inspection	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. Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Air Intake System Inspection	Inspect for a restriction in the air cleaner or the air intake ducts. Inspect for a restriction in the turbocharger charge air cooler. Inspect for a restriction in the intake manifold. Inspect for an air leak in the charge air cooler with a J 46091 Charge Air Cooler Tester. Inspect for an air leak in the air ducts between the turbocharger and the intake manifold.
Engine Mechanical Inspection	Inspect for incorrect basic engine parts such as the cam, the heads, the pistons, etc. Inspect for excessive oil entering the combustion chamber. Refer to Oil Consumption Diagnosis in Engine Mechanical - 6.6L (LLY).

Excessive Smoke (Black)

Circuit Description

Voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

MIL Operation

The MIL is located on the instrument panel cluster (IPC).

MIL Function

The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
The MIL illuminates during a bulb test and a system test.
A DTC will be stored if a MIL is requested by the ECM.

MIL Illumination

The MIL will illuminate with the ignition switch ON and the engine not running.
The MIL will turn OFF when the engine is started.
The MIL will remain ON if the self-diagnostic system has detected a malfunction.
The MIL may turn OFF if the malfunction is not present.
If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated as long as the ignition switch is ON.
If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Test Description

The number below refers to the step number on the diagnostic table.

4: This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check - Vehicle?		Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Verify whether the instrument cluster is operational. Command the malfunction indicator lamp (MIL) ON and OFF with a scan tool. Does the MIL turn ON and OFF when commanded with a scan tool?		Go to Intermittent Conditions	Go to Step 3
3	Inspect the fuse that supplies battery voltage to the cluster. Is the fuse open?		Go to Step 10	Go to Step 4
4	Turn OFF the ignition. Remove the fuse that supplies battery voltage to the cluster. Disconnect the engine control module (ECM). Turn ON the ignition with the engine OFF. Measure the voltage from the MIL control circuit in the ECM harness connector to a good ground. Is the voltage less than the specified value?	1.0 V	Go to Step 5	Go to Step 11
5	Turn OFF the ignition. Install the fuse that supplies battery voltage to the cluster. Turn ON the ignition with the engine OFF. Connect a 3-amp fused jumper wire between the MIL control circuit in the ECM harness connector and a good ground. Is the MIL illuminated?		Go to Step 9	Go to Step 6
6	Turn OFF the ignition. Remove the instrument panel cluster (IPC). Refer to Instrument Panel (I/P) Carrier Replacement in Instrument Panel, Gages, and Console. Turn ON the ignition, with the engine OFF. Probe the ignition voltage circuit of the IPC harness connector with a test lamp that is connected to a good ground. Does the test lamp illuminate?		Go to Step 7	Go to Step 12
7	Test the MIL control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct a condition?		Go to Step 15	Go to Step 8
8	Test for an intermittent and for a poor connection at the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?		Go to Step 15	Go to Step 13
9	Test for an intermittent and for a poor connection at the ECM. Refer to Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?		Go to Step 15	Go to Step 14
10	Test all circuits and components that are supplied by this fuse for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?		Go to Step 15	Go to Intermittent Conditions
11	Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?		Go to Step 15
12	Repair the open in the battery voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?		Go to Step 15
13	Replace the IPC. Refer to Instrument Panel (I/P) Carrier Replacement in Instrument Panel, Gages and Console. Did you complete the replacement?		Go to Step 15
14	Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement?		Go to Step 15
15	Turn OFF the ignition for 30 seconds. Start the engine. Does the MIL operate correctly?		Go to Step 16	Go to Step 2
16	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK

Malfunction Indicator Lamp (MIL) Inoperative

Ignition voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.

The MIL is located on the instrument panel (I/P).

MIL Function

The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
The MIL illuminates during a bulb test and a system test.
A DTC will be stored if a MIL is requested by the ECM.

MIL Illumination

The MIL will illuminate with ignition switch ON and the engine not running.
The MIL will turn OFF when the engine is started.
The MIL will remain ON if the self-diagnostic system has detected a malfunction.
The MIL may turn OFF if the malfunction is not present.
If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.
If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Diagnostic Aids

If the problem is intermittent, refer to Intermittent Conditions .

The number below refers to the step number on the diagnostic table.

2: This step determines if the condition is with the MIL control circuit or the ECM.

Step	Action	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check - Vehicle?	Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Turn OFF the ignition. Disconnect the engine control module (ECM). Turn ON the ignition, with the engine OFF. Observe the malfunction indicator lamp (MIL). Is the MIL illuminated?	Go to Step 3	Go to Step 5
3	Remove the instrument panel cluster (IPC). Refer to Instrument Panel (I/P) Carrier Replacement in Instrument Panel, Gages, and Console. Test the MIL control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 6	Go to Step 4
4	Replace the IPC. Refer to Instrument Panel (I/P) Carrier Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement?	Go to Step 6
5	Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement?	Go to Step 6
6	Turn the ignition OFF for 30 seconds. Start the engine. Does the vehicle operate correctly without any MIL illumination, and without any stored DTCs?	System OK	Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Malfunction Indicator Lamp (MIL) Always On

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis.

The Engine Cranks But Does Not Run diagnostic table assumes the following

The batteries are completely charged. Refer to «Battery Inspection/Test (Non-HP2)»(ref-197377-S33118019212005101100000) or «Battery Inspection/Test (HP2)»(ref-197377-S30888150552005101100000) in Engine Electrical.
The cranking speed is within specifications. Refer to «Engine Cranks Slowly»(ref-197377-S15604229122005101100000) in Engine Electrical.
There is adequate fuel in the fuel tanks.

If the cause of an engine cranks but will not run condition has not been found, inspect for the following conditions

Hard starting only in cold ambient temperatures. These may cause an intermittent condition that may not occur in the service bay: Fuel heater inoperative-Refer to «Fuel Heater Inoperative»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis) . Ice blockage at the fuel pickup in the fuel tank-This will be a high vacuum in the supply lines while cranking, and the problem will disappear after the vehicle is brought in the service bay. It may also exhibit a start and stall condition or a starting condition with no acceleration.
The correct cranking speed is 100 RPM cold and 180 RPM hot.
Water or foreign material in fuel system
A basic engine problem
More than 1 ohm of resistance in the ignition 1 voltage circuit to the fuel injection control module may cause a crank no start condition.
Low engine coolant may cause the engine to shut down.

The numbers below refer to the step numbers on the diagnostic table.

5: This step tests for an ignition 1 voltage supply to the engine control module (ECM).
6: If there is fuel in the engine oil, fuel may be leaking from the fuel injector or fuel injection pump into the crankcase.
7: If the fuel system will not even briefly prime to 10 psi and will not start, the check valve in the fuel filter/heater element housing is stuck open.
8: This step determines if the fuel system is bleeding down causing a no start. The fuel pressure will slowly drop to 0 psi, but should still be above 8 psi 10 seconds after pressurizing the fuel system.
9: In some cases, no compression, possibly with excessive fuel, in a single cylinder can cause a no start.
10: This step determines if the problem is a stuck open or broken fuel injector. If fuel vapors come out of any of the glow plug holes, excessive fuel is being sent into a cylinder, and not being distributed to all of the fuel injectors.
11: The engine will not run without an actual fuel rail pressure more than 10 MPa (1,450 psi).

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?		Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Turn ON the ignition, with the engine OFF. Observe the DTC Information with a scan tool. Does the scan tool display DTC P0090, P0193, P0335, P0336, P0340, P0370, P0374, P0601, P0602, P0603, P0604, P0611, P0612, P0642, P0643, P0670, P0698, P0699, P1621, P1626, P1631, P1683, P1687, or U0105?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 3
3	Is the customer's concern with a fuel smell or fuel leak?		Go to Fuel Leaks	Go to Step 4
4	Observe the Actual Fuel Rail Pressure parameter with a scan tool. Is the pressure within the specified range?	1-1.8 MPa	Go to Step 5	Go to Step 15
5	Observe the Ignition 1 signal parameter with a scan tool. Is the Ignition 1 signal parameter at the specified value?	B+	Go to Step 6	Go to Step 18
6	Inspect for the following conditions: Excessive fuel in the engine oil-Refer to Fuel in Engine Oil in Engine Mechanical. Fuel specific gravity-Refer to Contaminants-in-Fuel Diagnosis . Did you find and correct the condition?		Go to Step 26	Go to Step 7
7	Install the J 44638 Vacuum Gage to the fuel system service port on the right front side of the engine. Special Tools . Attempt to hand prime the fuel manager 30 times or until the specified pressure is reached. Can you prime the system to the specified value?	8 psi	Go to Step 8	Go to Step 23
8	Does the pressure measure more than the specified value for more than 2 minutes?	2 psi	Go to Step 9	Go to Step 12
9	Perform the Engine Compression Test. Refer to Engine Compression Test in Engine Mechanical. Repair the engine as necessary. Did you find and correct the condition?		Go to Step 27	Go to Step 10
10	Did any of the cylinders emit any fuel vapor during the Engine Compression Test?		Go to Step 22	Go to Step 11
11	Crank the engine for 15 seconds. Observe the Actual Fuel Rail Pressure parameter with a scan tool. Is the Actual Fuel Rail Pressure parameter more than the specified value?	10 MPa (1,450 psi)	Go to Step 13	Go to Step 12
12	Prime the fuel manager to 10 psi. Attempt to start the engine while the prime is still above 8 psi. Does the engine start?		Go to Fuel System Diagnosis	Go to Fuel System Diagnosis - High Pressure Side
13	IMPORTANT: If there is high resistance in the signal or low reference circuits of the crankshaft position (CKP) sensor the Engine Speed parameter of the scan tool will display a value more than 0. It will not be an accurate measure of engine speed, and can cause an Engine Cranks but does Not Run condition. Test the CKP sensor signal and low reference circuits for high resistance. Refer to Circuit Testing in Wiring Systems.Did you find and correct the condition?		Go to Step 26	Go to Step 14
14	Inspect for the following conditions: A plugged air filter A collapsed air intake duct The fuel heater is inoperative. If the customer concern is that the engine will not start when ambient temperatures are less than 2-4°C (35-40°F), refer to Fuel Heater Inoperative . A restricted exhaust system-Refer to Symptoms - Engine Exhaust in Engine Exhaust. Did you find and correct the condition?		Go to Step 26	Go to Diagnostic Aids
15	Disconnect the fuel rail pressure sensor. Observe the Actual Fuel Rail Pressure parameter on the scan tool. Does the Actual Fuel Rail Pressure parameter measure more than the specified value?	175 MPa	Go to Step 17	Go to Step 16
16	Test the fuel rail pressure sensor signal circuit for a short to ground. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition?		Go to Step 26	Go to Step 21
17	Test the fuel rail pressure sensor circuits for high resistance. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition?		Go to Step 26	Go to Step 19
18	Test the ignition 1 voltage circuit of the engine control module (ECM) for a short to ground, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Replace the fuse, if necessary. Did you find and correct the condition?		Go to Step 26	Go to Step 20
19	Test for an intermittent or for a poor connection at the fuel rail pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?		Go to Step 26	Go to Step 24
20	Clean and tighten the ECM shared ground. Refer to Power and Grounding Component Views in Wiring Systems. Attempt to start the engine. Does the engine start?		Go to Step 26	Go to Step 21
21	Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?		Go to Step 26	Go to Step 25
22	IMPORTANT: When the fuel injector pressure lines are removed, debris will fall on the fuel injector inlet fitting. Vacuum the debris from the area to prevent the debris from falling in the fuel injector. Replace the fuel injectors on the affected cylinders. Refer to Fuel Injector Replacement (Left) or Fuel Injector Replacement (Right) .Did you complete the replacement?		Go to Step 26
23	IMPORTANT: Before replacing the fuel filter/heater element housing, inspect the fuel vent screw for damage or cross threading. Replace the vent screw w/O-ring if either condition is found. Replace the fuel filter/heater element housing. Refer to Fuel Filter/Heater Element Housing Replacement .Did you complete the replacement?		Go to Step 26
24	Replace the fuel rail pressure sensor. Refer to Fuel Rail Pressure (FRP) Sensor Replacement . Did you complete the replacement?		Go to Step 26
25	Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement?		Go to Step 26
26	Clear any DTCs with a scan tool. Attempt to start the engine. Does the engine start and continue to run?		Go to Step 27	Go to Step 2
27	Allow the engine to idle until normal operating temperature is reached. Observe the DTC Information with a scan tool. Are any DTCs displayed?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK

IMPORTANT
If there is high resistance in the signal or low reference circuits of the crankshaft position (CKP) sensor the Engine Speed parameter of the scan tool will display a value more than 0. It will not be an accurate measure of engine speed, and can cause an Engine Cranks but does Not Run condition.

IMPORTANT
When the fuel injector pressure lines are removed, debris will fall on the fuel injector inlet fitting. Vacuum the debris from the area to prevent the debris from falling in the fuel injector.

IMPORTANT
Before replacing the fuel filter/heater element housing, inspect the fuel vent screw for damage or cross threading. Replace the vent screw w/O-ring if either condition is found.

Engine Cranks but Does Not Run

Fuel Pressure Regulator Diagnosis

The Fuel Pressure Regulator graphing procedure offers valuable information on regulator performance by comparing desired and actual fuel rail pressure. An almost perfect comparison between actual rail pressure and desired rail pressure is found on a fairly new, low mileage engine. A minor ripple is acceptable behavior for the fuel rail pressure regulator and is seen on high mileage engines. A "shark tooth" fluctuation in actual fuel rail pressure indicates a sticking pressure regulator.

Set up the following Min/Max ranges for graphing the fuel rail pressure on the scan tool. Engine Speed Min/Max range is 0-1,000 RPM. Actual Fuel Rail Pressure Min/Max range is 1-160 MPa. Desired Fuel Rail Pressure Min/Max is 1-160 MPa.
Start and idle the engine.
Observe the live plot for sharp changes or shark tooth pattern in the Actual Fuel Rail Pressure while performing the following actions: Idling the engine Shifting the transmission from Park to Drive and back to Park Turning the steering from left stop position to right stop position Turning the air conditioning ON and OFF
If there is a violent fluctuation in the Actual Fuel Rail Pressure, as seen in the surging graph below, replace the fuel pressure regulator. Refer to «Fuel Pressure Regulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) .

Scheme 217

Callout	Component Name
1	Engine Speed
2	Actual Fuel Rail Pressure
3	Desired Fuel Rail Pressure

Scheme 218

Callout	Component Name
1	Engine Speed
2	Actual Fuel Rail Pressure
3	Desired Fuel Rail Pressure

Scheme 219

Callout	Component Name
1	Engine Speed
2	Actual Fuel Rail Pressure
3	Desired Fuel Rail Pressure

Fuel System Description

Fuel is drawn by the supply pump through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame. The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter/heater element housing, which combines a water separator, a prime pump, a fuel heater element and a filter element. The fuel is then delivered to the high-pressure pump. An integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes the fuel supply pump and the high-pressure pump. If the fuel system is not suppling enough fuel, a driveability concern may occur. If air is being drawn into the fuel injection system, a Cranks But Will Not Run or Hart Start symptom could exist.

High Pressure System

The much larger section of the pump assembly is the high-pressure fuel injection pump. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the pressurized flows to the left common fuel rail. A balance pipe from the center of the left rail then feeds the right common fuel rail. Each common fuel rail supplies one bank of 4 fuel injectors. The fuel rail pressure sensor is mounted in the middle of the right common fuel rail.

Return System

The fuel return system routes fuel from the fuel injectors and the fuel injection pump. The fuel rail pressure relief valve is located in the rear of the left common rail. The return fuel travels to the fuel cooler and then to the fuel tank. This fuel is used to cool and lubricate the injection pump and the injectors.

The following conditions may cause an air leak into the fuel supply system

Deformed or cut O-rings at the fuel supply line connections
Improperly seated fuel supply line fittings
Porous or weathered rubber fuel supply lines

Step	Action	Yes	No
1	IMPORTANT: Ensure that a sufficient amount of fuel is in the fuel tank to run the vehicle. Install the J 44638 Vacuum Gage to the fuel system service port on the right front side of the engine. Special Tools . Prime the fuel system until 10 psi is indicated on the J 44638 . Special Tools . IMPORTANT: It may be necessary to remove engine components for the visual inspections. Visually inspect the following items for restrictions or leaks: Fuel injector control module fuel line connections Hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel Fuel leaks between the fuel filter/heater element housing and the fuel injection pump Did you find and correct the condition?	Go to Step 21	Go to Step 2
2	Does the fuel system pressure drop below 2 psi in less than 1 minute?	Go to Step 12	Go to Step 3
3	Disconnect the fuel supply line at the engine. Refer to Quick Connect Fitting(s) Service (Metal Collar) . Cap off the fuel supply pipe on the engine with a rubber plug and clamp. Disconnect the fuel return line at the engine. Refer to Quick Connect Fitting(s) Service (Metal Collar) . Install a J 23738-A Mityvac on the fuel return pipe on the engine. Apply at least 25 inches Hg of vacuum to the fuel return pipe and wait for at least 1 minute for the system to stabilize. Repeat this step 6 additional times. Does the J 23738-A gage indicate that vacuum dropped below 8 inches Hg of vacuum within 10 minutes?	Go to Step 7	Go to Step 4
4	Connect the fuel supply line at the engine. Disconnect the chassis fuel supply line from the fuel sender at the fuel tank. Refer to Quick Connect Fitting(s) Service (Metal Collar) . Plug the chassis fuel supply line. Apply at least 25 inches Hg of vacuum to the fuel return pipe with the J 23738-A and wait more than 1 minute for the system to stabilize. Repeat the previous step 10 times. Observe the J 23738-A . Does the vacuum drop below 8 Hg of vacuum within 10 minutes?	Go to Step 15	Go to Step 5
5	Reconnect the return line at the engine. Install a transparent hose between the fuel injection control module (FICM) outlet and the fuel filter inlet with a vertical loop to observe the incoming fuel for air bubbles. Install all components and lines that were previously disconnected or removed. Prime the fuel system 30 times to remove the air from the fuel hoses. Attempt to start the engine. Did the engine start?	Go to Step 6	Go to Step 12
6	Run the engine for at least 10 minutes to allow the fuel system to stabilize, and purge any air from the system. Observe the fuel in the transparent hose. Are there any air bubbles entering the transparent hose?	Go to Step 10	Go to Step 21
7	Disconnect the fuel outlet hose from the outlet pipe of the fuel filter/heater element housing. Open the drain on the fuel filter/heater element housing and drain the fuel into a suitable container. Close the drain. Install a J 23738-A on the outlet port of the fuel filter/heater element housing. Apply 15 inches Hg of vacuum to the fuel pipe and observe the gage. Does the vacuum drop?	Go to Step 13	Go to Step 8
8	Connect the fuel supply line at the engine. Remove the J 23738-A from the outlet port of the fuel filter assembly and install it on the fuel outlet hose. Remove the supply hose from the fuel injection pump and plug the hose. Apply 15 inches Hg of vacuum and observe the reading. Does the vacuum drop?	Go to Step 16	Go to Step 9
9	Disconnect the fuel injection pump return hose. Cap off the fuel return pipe on the fuel injection pump with a rubber plug, and clamp the plug. Install a J 23738-A to the fuel inlet pipe of the fuel injection pump. Apply 20 inches Hg of vacuum and observe the reading. Does the vacuum drop?	Go to Step 18	Go to Step 17
10	Remove the front fuel tank. Refer to Fuel Tank Replacement (Pickup) or Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . Remove the fuel sender from the fuel tank. Refer to Fuel Sender Assembly Replacement . Remove the strainer from the fuel sender and plug the bottom end of the pickup tube. Install a J 23738-A to the upper end of the pickup tube. Apply 15 inches Hg of vacuum and observe the reading. Does the vacuum drop?	Go to Step 20	Go to Step 11
11	Install the fuel sender, fuel tank and connect all fuel system connections that were previously disconnected. Refer to Fuel Sender Assembly Replacement and Fuel Tank Replacement (Pickup) or Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . Prime the fuel system 30 times, or until fuel pressure is 10 psi, to remove the air from the fuel system. Air will be forced out of the system within 2 minutes. Start and run the engine. Observe the fuel entering the transparent hose for air bubbles. Are any air bubbles present in the transparent hose?	Go to Diagnostic Aids	Go to Step 21
12	Prime the fuel system 30 times, or until fuel pressure is 10 psi, to remove the air from the fuel system. Air will be forced out of the system within 2 minutes. Remove the hose from the fuel filter/heater element housing outlet fitting and plug the hose. Verify that the J 44638 is installed. Special Tools . Remove the ignition 1 relay. Crank the engine 2-3 times in 15-second intervals and observe the J 44638 . Special Tools . Does the J 44638 indicate more than 5 inches Hg of vacuum?. Special Tools .	Go to Step 21	Go to Step 18
13	Disconnect the fuel supply line from the fuel filter/heater element housing port. Install the J 23738-A to the fuel supply line. Apply 15 inches Hg of vacuum and observe the reading. Does the vacuum drop?	Go to Step 14	Go to Step 19
14	Repair the air leak in the fuel supply pipe on the engine. Did you complete the repair?	Go to Step 21
15	Repair the air leak in the fuel supply line between the engine and the fuel tank sending unit. Did you complete the repair?	Go to Step 21
16	Repair the leak between the fuel filter/heater element housing outlet and the fuel injection pump inlet. Did you complete the repair?	Go to Step 21
17	Replace the fuel injection pump inlet supply hose. Refer to Fuel Hose Replacement - Fuel Injection Pump to Fuel Feed Block . Did you complete the replacement?	Go to Step 21
18	Replace the fuel injection pump. Refer to Fuel Injection Pump Replacement . Did you complete the replacement?	Go to Step 21
19	IMPORTANT: Before replacing the fuel filter/heater element housing, inspect the fuel vent screw for damage or cross threading. Replace the vent screw with O-ring if either condition is found. Replace the fuel filter/heater element housing. Refer to Fuel Filter/Heater Element Housing Replacement .Did you complete the replacement?	Go to Step 21
20	Replace the fuel tank sending unit. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement?	Go to Step 21
21	Remove the transparent hose, if necessary, and attach any disconnected components or fuel lines. Clean any fuel spills. Prime the fuel system 30 times to remove the air in the fuel hoses. Start the engine. If the engine starts and stalls, prime fuel system an additional 30 times. Run the engine to ensure no fuel leaks exist. Is the customer concern corrected?	System OK	Go to Symptoms - Engine Controls

IMPORTANT
Ensure that a sufficient amount of fuel is in the fuel tank to run the vehicle.

IMPORTANT
It may be necessary to remove engine components for the visual inspections.

IMPORTANT
Before replacing the fuel filter/heater element housing, inspect the fuel vent screw for damage or cross threading. Replace the vent screw with O-ring if either condition is found.

Fuel System Diagnosis

Fuel is drawn by the supply pump through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame. The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter/heater element housing, which combines a water separator, a prime pump, fuel heater element and a filter element. The fuel is then delivered to the high-pressure pump. An integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes the fuel supply pump and the high-pressure pump. If the fuel system is not suppling enough fuel a driveability concern may occur. If air is being drawn into the fuel injection system, a Cranks But Will Not Run or Hart Start symptom could exist.

The much larger section of the pump assembly is the high-pressure fuel injection pump. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the pressurized flows to the left common fuel rail. A balance pipe from the center of the left rail then feeds the right common fuel rail. Each common fuel rail supplies one bank of 4 fuel injectors. The fuel rail pressure (FRP) sensor is mounted in the middle of the right common fuel rail.

The Fuel Return System routes fuel from the fuel injectors and the fuel injection pump. The FRP relief valve is located in the rear of the left common rail. The return fuel travels to the fuel cooler and then to the fuel tank. This fuel is used to cool and lubricate the injection pump and the injectors.

Bent or pinched fuel return lines on the engine can cause a restricted fuel return flow.

Step	Action	Yes	No
1	IMPORTANT: Do not apply more than the specified air pressure to the return line. Disconnect the return line at the engine. Refer to Quick Connect Fitting(s) Service (Metal Collar) . Remove the fuel filler cap. Apply 1 psi air at the fuel return line that leads back to the tank. Listen at the filler tube for air flowing from the tank. Did air flow from the filler tube?	Go to Step 6	Go to Step 2
2	Disconnect the return line at the fuel sender assembly. Retest using 1 psi at the fuel return line back to the tank. Did air flow from the return line?	Go to Step 3	Go to Step 4
3	Replace the fuel sender assembly. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement?	Go to Step 6
4	Lift the vehicle. Refer to Lifting and Jacking the Vehicle in General Information. Inspect the return line for restrictions between the fuel tank and engine. Did you find and correct the condition?	Go to Step 6	Go to Step 5
5	Replace the fuel return line between the engine and the fuel tank. Refer to Fuel Return Pipe Replacement . Did you complete the replacement?	Go to Step 6
6	Install and connect all components or fuel lines that were previously removed or disconnected. Operate the vehicle in order to verify the repairs. Did you correct the condition?	System OK	Go to Diagnostic Aids

IMPORTANT
Do not apply more than the specified air pressure to the return line.

Fuel Return System Diagnosis

Fuel Leaks

Remove the air cleaner assemble. Refer to «Air Cleaner Assembly Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) .
Clean all of the fuel lines between the fuel injection pump and the fuel injectors using brake cleaning solvent, and let dry.
Add 8 ounces of oil dye to the fuel tank. On dual tanks, add the dye to the front, or primary tank. Refer to «Fuel System Description»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction__fuel-system-description) .
Start and idle the engine for 3-5 minutes.
Command the fuel pressure control to 160 MPa (23,206 psi) with a scan tool.
Inspect for fuel leaks around the fuel injection pump, fuel rails, and fuel injector supply lines with a J 28428-E High Intensity Black Light Kit. Tighten or replace any leaking lines or components. Refer to the following: «Fastener Tightening Specifications»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction__fastener-tightening-specifications) «Fuel Injection Line Routing Diagram»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Injector Return Pipe Replacement - Left»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Injector Return Pipe Replacement - Right»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Return Pipe Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Rail Assembly Replacement - Bank 1»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Rail Assembly Replacement - Bank 2»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Return Junction Block Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Injection Pump Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Injector Replacement (Left)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) «Fuel Injector Replacement (Right)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction)
A fuel leak may be caused by restricted return fuel lines. Refer to «Fuel Return System Diagnosis»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-troubleshooting-diagnosis) .

Supply System

The fuel flows through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame. The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter assembly, which combines a water separator, a hand prime pump and a filter element. Within the assembly, there is also a fuel heater. The integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes a fuel supply pump and a high-pressure pump. Fuel is drawn to the supply pump from the primary fuel tank by the supply pump and delivered to the high-pressure pump.

The much larger section of the fuel injection pump assembly is the high-pressure pump. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the fuel flows to the 2 common fuel rails. Each common fuel rail supplies one bank of 4 fuel injectors.

The fuel return system routes fuel from the fuel injectors, the pressure relief valve, and the fuel injection pump. The return fuel travels to the fuel cooler and then to the fuel tank. This fuel is used to cool and lubricate the injection pump and the injectors.

The fuel return volumes vary based on the American Petroleum Institute (API) rating of the diesel fuel.
A fuel injector may have high fuel return flow only at higher engine temperatures.

Step	Action	Yes	No
1	Were you referred to this test from the Engine Cranks but Does Not Run diagnostic?	Go to Step 3	Go to Step 2
2	Remove the fuel return rubber hose from the rear of the left fuel rail and plug the hose to prevent fuel leakage. Install a section of rubber fuel hose on the fuel pressure relief valve connection and place it in a clean fuel container. Start and idle the engine. Command the fuel rail pressure to 160 MPa with a scan tool. Observe the fuel hose and container for fuel leakage. Did fuel flow into the container?	Go to Step 12	Go to Step 4
3	IMPORTANT: If you were not referred to this test from another diagnostic, do not perform this procedure. Only perform this test when the fuel is more than 18°C (65°F). Remove the air duct from the air cleaner assembly and the turbo inlet. Remove the fuel return rubber hose from the rear of the left fuel rail and plug the hose to prevent fuel leakage. Remove the relay that supplies ignition 1 voltage to the fuel injection control module (FICM). Crank the engine for 15 seconds while observing the fuel pressure relief valve hose connection for fuel leakage. Did fuel leak from the fuel pressure relief valve at the hose connection?	Go to Step 12	Go to Step 4
4	IMPORTANT: The engine cranking speed must be more than 150 RPM during the cranking portion of this test. Always replace the fuel return hose retaining clips on the fuel injectors with new clips after removing. Remove the relay that supplies the ignition 1 voltage to the FICM, if it was not previously removed. Remove the fuel return hose from the fuel injectors of the right cylinder bank. Refer to Fuel Injector Return Pipe Replacement - Right . Connect the yellow hoses from the J 45873 Fuel Return Volume Test Kit to the J 45873-30 Fuel Injector Test Adapters. Special Tools . Connect the J 45873-30 with yellow hoses to each fuel injector return port of the right cylinder bank, and install the retaining clips. Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical order. Special Tools . Connect the fuel return hoses to the J 45873-30 to prevent leakage. Crank the engine in 15-second intervals, with 1 minute cooling time between intervals, until fuel starts to flow into all of the graduated cylinders. Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container. Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical order. Special Tools . Crank the engine for 15 seconds. Measure the quantity of fuel in each of the graduated cylinders. Refer to Fuel System Specifications for the desired quantities. Were any of the fuel quantities more than the specified values?	Go to Step 5	Go to Step 6
5	Remove the fuel feed pipes from any fuel injectors that have high return flow and install the EN 47589 Fuel Pressure Adapter Cap to the fuel rail outlets. Special Tools . Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container. Install the 4 yellow hoses in the graduated cylinders in numerical order. Crank the engine for 15 seconds. Using the Retesting Fuel Injector Return Flow Values table, measure the quantity of fuel in each of the graduated cylinders. Refer to Fuel System Specifications for the desired quantities. Remove the fuel feed pipes from any uncapped fuel injectors that have high return flow and install the EN 47589 to the fuel rail outlets. Special Tools . Did you complete the action?	Go to Step 6
6	IMPORTANT: The engine cranking speed must be more than 150 RPM during the cranking portion of this test. Always replace the fuel injector return hose retaining clip. Remove the fuel return hoses from the fuel injectors of the left cylinder bank. Refer to Fuel Injector Return Pipe Replacement - Left . Connect the yellow hoses from the to the J 45873-30. Connect the J 45873-30 with yellow hoses to each fuel injector return port of the left cylinder bank, and install the retaining clips. Connect the fuel return hoses to the J 45873-30 to prevent leakage. Crank the engine in 15-second intervals, with 1 minute cooling time between intervals, until fuel starts to flow into all of the graduated cylinders. Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container. Install the 4 yellow hoses in the graduated cylinders in numerical order. Crank the engine for 15 seconds. Measure the quantity of fuel in each of the graduated cylinders. Refer to Fuel System Specifications for the desired quantities. Were any of the fuel quantities more than the specified values?	Go to Step 8	Go to Step 7
7	Were any fuel injector lines capped off during either cylinder bank testing?	Go to Step 10	Go to Step 11
8	Remove the fuel feed pipes from any fuel injectors that have high return flow and install the EN 47589 to the fuel rail outlets. Special Tools . Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container. Install the 4 yellow hoses in the graduated cylinders in numerical order. Crank the engine for 15 seconds. Using the Retesting Fuel Injector Return Flow Valves table, measure the quantity of fuel in each of the graduated cylinders. Refer to Fuel System Specifications for the desired quantities. Were the fuel quantities more than the specified value at the uncapped fuel injectors?	Go to Step 9	Go to Step 10
9	Repeat the fuel injector return flow test with capping until no fuel injectors have high return fuel flow. Did you complete the action?	Go to Step 10
10	Replace the fuel injectors that had capped off lines. Refer to Fuel Injector Replacement (Left) or Fuel Injector Replacement (Right) . Install all disconnected and removed fuel system components. Start and idle the engine. You may have to prime the fuel system before the engine will start. Command the fuel pressure control to 160 MPa with a scan tool. Is the fuel pressure more than 145 MPa?	Go to Step 13	Go to Step 11
11	Replace the fuel injection pump. Refer to Fuel Injection Pump Replacement . Did you complete the replacement?	Go to Step 13
12	Replace the fuel pressure relief valve. Refer to Fuel Pressure Relief Valve Replacement . Did you complete the replacement?	Go to Step 13
13	IMPORTANT: The fuel system may have to be primed before starting the engine. Install and connected all fuel system components that were previously removed or disconnected. Operate the vehicle in order to verify the repairs. Did you correct the condition?	System OK	Go to Symptoms - Engine Controls

IMPORTANT
If you were not referred to this test from another diagnostic, do not perform this procedure. Only perform this test when the fuel is more than 18°C (65°F).

IMPORTANT
The engine cranking speed must be more than 150 RPM during the cranking portion of this test. Always replace the fuel return hose retaining clips on the fuel injectors with new clips after removing.

IMPORTANT
The engine cranking speed must be more than 150 RPM during the cranking portion of this test. Always replace the fuel injector return hose retaining clip.

IMPORTANT
The fuel system may have to be primed before starting the engine.

Fuel System Diagnosis - High Pressure Side

The Fuel Injector Balance test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical DTCs. During the Cylinder Power Balance portion of the test, the engine control module (ECM) turns OFF individual injectors while the engine is running and the scan tool displays engine RPM. The ECM adjusts for the drop in engine speed, so the power contribution of each cylinder must be felt by the technician. If a fuel injector is turned OFF and there is a different power contribution observed when compared to the other cylinders, that cylinder is identified with the complaint. If the customer complaint occurs during idle or during off-idle tip in acceleration, the balance rates are used to identify the cylinder with a fault related to the fuel injector or engine compression. If a fuel injector is turned OFF and the engine noise or smoke disappears, that cylinder has a fuel injector or engine compression condition.

The numbers below refer to the step numbers on the diagnostic table.

4: The balance rate adjustments are utilized by the ECM only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. A positive value indicates that fuel is being added to each cylinder event, such as with poor engine compression or a fuel injector that is not flowing enough fuel. A negative value indicates fuel being removed from each cylinder event, such as a fuel injector that is flowing too much fuel. The balance rates will change depending on if the transmission is in Neutral or Drive.
5: This step determines if the ECM can control a stable fuel pressure. A high balance rate may be caused by a fuel injector or compression only if the ECM can control fuel pressure.
6: The Cylinder Power Balance Test may be performed at any engine speed or load from idle to wide open throttle (WOT). There is a 5 minute time limit for each test. The ECM and scan tool must both be powered down to reset the timer.

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?		Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Are any DTCs set other than P0300, P0301-P0308?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 3
3	Does the customer concern occur at idle or during tip-in acceleration off-idle?		Go to Step 4	Go to Step 6
4	Start and run the engine until the engine coolant temperature (ECT) is more than 82°C (180°F). Turn OFF all accessories. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied. Place the transmission in Drive. Idle the engine for more than 30 seconds. Record the Balancing Rate Cyl.1-8 parameters from the scan tool while the engine is at idle speed. Repeat steps 2-6 with the transmission in Neutral. Are all of the Balancing Rate parameters within the first specified range in Drive, and the second specified range in Neutral?	6 mm 3 and +6 mm 3 -4 mm 3 and +4 mm 3	Go to Step 6	Go to Step 5
5	Graph the Fuel Pressure Regulator. Refer to Fuel Pressure Regulator Diagnosis . Is the fuel pressure regulator graph normal?		Go to Step 7	Go to Step 9
6	IMPORTANT: The fuel Cylinder Power Balance Test must be performed under the conditions for which the concern occurred. The concern must be duplicated during the test. IMPORTANT: DO NOT operate the cruise control during this test. Cruise control reactivation after the test may cause a brief extreme increase in engine speed. Observe the cylinder power contribution or other customer concern. Perform the Cylinder Power Balance Test in Special Functions. Do any of the cylinders indicate a different cylinder power contribution than the others, or lessen the customer concern?		Go to Step 7	System OK
7	IMPORTANT: A fuel injector leak into the combustion chamber may result in mechanical damage to the cylinder. If any fuel spray comes out of a glow plug hole during the compression test, replace the fuel injector of the affected cylinder. Perform the Engine Compression test. Refer to Engine Compression Test in Engine Mechanical - 6.6L.Do any of the cylinders have low compression?		Go to Symptoms - Engine Mechanical in Engine Mechanical - 6.6L	Go to Step 8
8	IMPORTANT: Refer to Injection System Components in Engine Controls Component Views . Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector. Replace the fuel injectors on the cylinders that had poor cylinder power contribution, high balance rates, or a noise/smoke change. Refer to Fuel Injector Replacement (Left) or Fuel Injector Replacement (Right) .Did you complete the replacements?		Go to Step 10
9	Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Did you complete the replacement?		Go to Step 10
10	Operate the vehicle under the conditions in which the concern occurred. Does the system operate normally, with no DTCs or symptoms?		System OK	Go to Symptoms - Engine Controls

IMPORTANT
The fuel Cylinder Power Balance Test must be performed under the conditions for which the concern occurred. The concern must be duplicated during the test.

IMPORTANT
DO NOT operate the cruise control during this test. Cruise control reactivation after the test may cause a brief extreme increase in engine speed.

IMPORTANT
A fuel injector leak into the combustion chamber may result in mechanical damage to the cylinder. If any fuel spray comes out of a glow plug hole during the compression test, replace the fuel injector of the affected cylinder.

IMPORTANT
Refer to Injection System Components in Engine Controls Component Views . Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector.

Fuel Injector Balance Test with Tech 2 (with Automatic Transmission)

The numbers below refer to the step numbers on the diagnostic table.

2: If the majority of the balance rates are positive and high, the dual-mass flywheel is causing a harmonic vibration that is affecting the engine fuel control system.
3: A dual mass flywheel concern will cause the balance rates to be inaccurate. The transmission concerns must be repaired before any fuel system diagnostic can be performed.
4: The balance rates are only to be used to diagnose these specific concerns.
5: The balance rate adjustments are utilized by the ECM only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. A positive value indicates that fuel is being added to each cylinder event, such as with poor engine compression or a fuel injector that is not flowing enough fuel. A negative value indicates fuel being removed from each cylinder event, such as a fuel injector that is flowing too much fuel.
6: This step determines if the ECM can control a stable fuel pressure. A high balance rate may be caused by a fuel injector or compression only if the ECM can control fuel pressure.
7: The Cylinder Power Balance Test may be performed at any engine speed or load from idle to wide open throttle. There is a 5 minute time limit for each test. The ECM and scan tool must both be powered down to reset the timer.

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?		Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Start and run the engine until the engine coolant temperature is more than 82°C (180°F). Turn OFF all accessories. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied. Idle the engine for more than 30 seconds. Record the Balancing Rate Cyl.1-8 parameters from the scan tool while the engine is at idle speed. Are at least 5 of the Balancing Rate parameters more than the specified value?	+4 mm 3	Go to Engine Flywheel Replacement (Automatic Transmission) or Engine Flywheel Replacement (Manual Transmission) in Engine Mechanical - 6.6L	Go to Step 3
3	Are any DTCs set other than P0300, P0301-P0308?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 4
4	Does the customer concern occur at idle or during tip-in acceleration off-idle?		Go to Step 5	Go to Step 7
5	Start and run the engine until the engine coolant temperature (ECT) is more than 82°C (180°F). Turn OFF all accessories. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied. Idle the engine for more than 30 seconds. Record the Balancing Rate Cyl.1-8 parameters from the scan tool while the engine is at idle speed. Are all of the Balancing Rate parameters within the specified range?	4 mm 3 and +4 mm 3	Go to Step 7	Go to Step 6
6	Graph the fuel pressure regulator. Refer to Fuel Pressure Regulator Diagnosis . Is the fuel pressure regulator graph normal?		Go to Step 8	Go to Step 10
7	IMPORTANT: The fuel Cylinder Power Balance test must be performed under the conditions for which the concern occurred. The concern must be duplicated during the test. IMPORTANT: DO NOT operate the cruise control during this test. Cruise control reactivation after the test may cause a brief extreme increase in engine speed. Observe the cylinder power contribution or other customer concern. Perform the Cylinder Power Balance test in Special Functions. Do any of the cylinders indicate a different cylinder power contribution than the others, or lessen the customer concern?		Go to Step 8	System OK
8	IMPORTANT: A fuel injector leak into the combustion chamber may result in mechanical damage to the cylinder. If any fuel spray comes out of a glow plug hole during the compression test, replace the fuel injector of the affected cylinder. Perform the Engine Compression test. Refer to Engine Compression Test in Engine Mechanical - 6.6LDo any of the cylinders have low compression?		Go to Symptoms - Engine Mechanical in Engine Mechanical - 6.6L	Go to Step 9
9	IMPORTANT: Refer to Injection System Components in Engine Controls Component Views . Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector. Replace the fuel injectors on the cylinders that had poor cylinder power contribution, high balance rates, or a noise/smoke change. Refer to Fuel Injector Replacement (Left) or Fuel Injector Replacement (Right) .Did you complete the replacements?		Go to Step 11
10	Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Did you complete the replacement?		Go to Step 11
11	Operate the vehicle under the conditions in which the concern occurred. Does the system operate normally, with no DTCs or symptoms?		System OK	Go to Symptoms - Engine Controls

IMPORTANT
The fuel Cylinder Power Balance test must be performed under the conditions for which the concern occurred. The concern must be duplicated during the test.

IMPORTANT
DO NOT operate the cruise control during this test. Cruise control reactivation after the test may cause a brief extreme increase in engine speed.

IMPORTANT
A fuel injector leak into the combustion chamber may result in mechanical damage to the cylinder. If any fuel spray comes out of a glow plug hole during the compression test, replace the fuel injector of the affected cylinder.

IMPORTANT
Refer to Injection System Components in Engine Controls Component Views . Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector.

Fuel Injector Balance Test with Tech 2 (with Manual Transmission)

Fuel Tank Leak Test

The diagnosis of fuel odor may be a condition of a leaking fuel tank, filler neck or filler cap. A defective filler cap, a plugged or pinched vent pipe can cause a collapsed fuel tank. Loose mounting straps or foreign material in tank may be the cause of a rattle at the fuel tank.

Leak Check Procedure

CAUTION

Place a dry chemical (Class B) fire extinguisher near the area before performing a Fuel Tank Leak Check. Before removing the fuel tank for a suspected leak, make sure that the fuel pipes or the tubes are not leaking onto the tank. Once removed, make sure that the fuel is not leaking around the fuel sender O-ring. Failure to follow these precautions may result in personal injury.

This check requires the fuel sender and the O-ring to be installed.

Disconnect the battery cables.
Drain the fuel tank. Refer to «Fuel Tank Draining Procedure»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) .
Remove the fuel tank. Refer to «Fuel Tank Replacement (Pickup)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) or «Fuel Tank Replacement (Cab/Chassis - Front)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) or «Fuel Tank Replacement (Cab/Chassis - Rear)»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction) .
Cap the fuel feed tube and the fuel return tube on the fuel sender.
Connect a piece of hose to the filler tube nipple and plug the opposite end.
Submerge the tank in water or apply a soap solution to the outside of the tank.
Apply 35 kPa (5 psi) of air pressure to the vent hose of the fuel tank. A leak will show up as bubbles.

Contaminants-In-Fuel Diagnosis

Fungi and other microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system. These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated, when service station tanks are being filled, fungi are distributed throughout the tank and may be pumped into a vehicle.

Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom is fuel filter plugging, however various metal fuel system components including fuel sender assembly, pipes, fuel injectors, and fuel injection pump can corrode.

CAUTION

Avoid physical contact with the biocides in order to avoid personal injury.

If fungi have caused fuel system contamination, use a diesel fuel biocide to sterilize the fuel system. Do not exceed the dosage recommended on the label. Discontinue the use of a biocide when towing a trailer. It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing.

Steam cleaning may be necessary if most of the fungus growth cannot be removed with biocides.

The presence of water or gasoline in diesel fuel may also cause injection pump and fuel injector damage.

This procedure checks for the presence of water and gasoline in diesel fuel that may cause fuel injection pump and fuel injector damage.

Remove and inspect the fuel filter.

If water, gasoline or fungi/bacteria are not present, end the inspection.
If water or fungi/bacteria are present, go to Cleaning Water from the Fuel System. Refer to «Fuel System Cleaning»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction__fuel-system-cleaning) .
If gasoline is present, go to Cleaning Gasoline from the Fuel System. Refer to «Fuel System Cleaning»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/testing-diagnostics/#engine-controls-66l-introduction__fuel-system-cleaning) .

Description

Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the inspection/maintenance (I/M) emission inspection in order to renew license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that complies with the local area requirements.

Conditions for Updating the I/M System Status

Each system monitor requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a DTC. A system monitor completes when either all DTCs comprising the monitor have run and passed, or any DTC comprising the monitor has illuminated the malfunction indicator lamp (MIL). Once the monitor completes, the I/M System Status display will indicate YES in the Completed column. For example, when the Misfire Monitoring System Status display indicates YES, all of the misfire components have been diagnosed. The I/M System Status will indicate NO in the Completed column when any of the required DTCs for that system have not run. The following is a list of conditions that would set the I/M System Status indicators to NO

The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the system monitor.
The battery has been disconnected or discharged below operating voltage.
The control module power or ground has been interrupted.
The control module has been reprogrammed.
The control module DTCs have been cleared as part of a service procedure.

Monitored Emission Control Systems

The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following

Comprehensive component monitoring - Emission related inputs and outputs
EGR system
Misfire monitoring

For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table .

Step	Action	Yes	No
1	Perform the Diagnostic System Check - Vehicle in Vehicle DTC Information. IMPORTANT: Any DTCs set, even those not listed in the Inspection/Maintenance system DTC table, may prevent the required DTCs from running. Repair any DTCs or driveability concerns. Did you find and repair a DTC or driveability concern?	Go to Step 3	Go to Step 2
2	Review any service bulletins for software updates that may prevent the required DTCs from running. Perform any reprogramming or repairs indicated by the service bulletins. Was a reprogramming or repair service required?	Go to Inspection/Maintenance (I/M) Complete System Set Procedure	Go to Step 3
3	Observe the I/M System Status display, with a scan tool. Is more than one system indicating a NO status?	Go to Inspection/Maintenance (I/M) Complete System Set Procedure	Go to the I/M System Set Procedure for the indicated system that did not update to YES

IMPORTANT
Any DTCs set, even those not listed in the Inspection/Maintenance system DTC table, may prevent the required DTCs from running.

Inspection/Maintenance (I/M) System Check

Inspection/Maintenance (I/M) System DTC Table

System	DTCs Required to Set System Status to YES
EGR	DTC P0401
Misfire Monitoring	DTC P0300 (Federal Emissions) or DTC P0300 (California Emissions) DTC P0301-P0308 (Federal Emissions) or DTC P0301-P0308 (California Emissions)

Inspection/Maintenance (I/M) System DTC Table

The purpose of the inspection maintenance (I/M) Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M system monitors. When all system monitors are completed, the I/M System Status indicators are set to YES. Perform this procedure when more than one of the I/M System Status indicators are set to NO.

Conditions for Running

Cold start

The battery voltage is between 11-18 volts.
The engine coolant temperature (ECT) is between 60-96.75°C (140-206.2°F).
The intake air temperature (IAT) is more than 5.25°C (41.5°F).
The barometric pressure (BARO) is more than 74 kPa.

Step	Action	Values	Yes	No
1	Did you perform the Inspection/Maintenance (I/M) System Check?		Go to Step 2	Go to Inspection/Maintenance (I/M) System Check
2	Ensure the vehicle is within the Conditions for Running specified in the supporting text. Turn OFF all of the accessories, e.g., A/C, blower fan, etc. Set the vehicle parking brake. Verify the transmission is in PARK for automatic transmissions and NEUTRAL for manual transmissions. Start and allow the engine to idle for the specified time. Observe the I/M System Status with a scan tool. Did both of the I/M System Status indicators update to YES?	2 minutes	Go to Step 3	Go to the I/M System Set Procedure for the systems that did not update to YES
3	Observe the emission related DTC portion of the I/M System Status with a scan tool. Does the scan tool indicate any emission related DTCs set?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK

Inspection/Maintenance (I/M) Complete System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute an Inspection/Maintenance (I/M) system monitor for the Exhaust Gas Recirculation (EGR) system. The system monitor is comprised of the test results from one or more DTCs. This procedure may be used to set the EGR I/M System Status display on the scan tool to YES. The EGR I/M System Status display indicated whether or not the control module has completed the system monitor. The system monitor completes when either all DTCs comprising the monitor run and pass, or any DTC comprising the monitor illuminates the malfunction indicator lamp (MIL). If one of the DTCs comprising the monitor is set and the MIL is not illuminated, the necessary trips are required to illuminate the MIL before the monitor will complete. Once the monitor completes, the EGR I/M System Status display will be updated to YES.

The barometric pressure (BARO) is more than 74 kPa.
The engine coolant temperature (ECT) is between 60-96.75°C (140-206.2°F).
The intake air temperature (IAT) is more than 5.25°C (41.5°F).
The battery voltage is between 11-18 volts.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the system set procedure. If any DTCs do not run and no DTC is set, review the appropriate scan tool data list and service information. This will give an indication of why the DTCs do not run. Some may abort due to changes in the conditions while running. For example, changes in engine load, such as a cooling fan or A/C compressor clutch turning ON, may cause a DTC to abort. If the EGR I/M System Status does not update to YES, the procedure can be repeated until a YES status is achieved.

Step	Action	Yes	No
1	Did you perform the Inspection/Maintenance (I/M) System Check?	Go to Step 2	Go to Inspection/Maintenance (I/M) System Check
2	Ensure that the vehicle is within the Conditions for Running specified in the supporting text. Turn OFF all of the accessories, e.g., A/C, blower fan, etc. Start and allow the engine to idle for 2 minutes. Observe the I/M System Status display with a scan tool. Did the Exhaust Gas Recirculation (EGR) System Status update to YES?	Go to Step 5	Go to Step 3
3	Observe the DTC Information with a scan tool. Does the scan tool indicate any failed DTCs?	Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 4
4	Refer to Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run in order to update the EGR I/M System Status to YES. Observe the Not Ran Since Code Cleared display with a scan tool. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the Specific DTC menu of the scan tool. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC. Repeat numbers 4 and 5 of this step for any additional required DTCs that have not run. Observe the I/M System Status display with a scan tool. Did the EGR System Status update to YES?	Go to Step 5	Go to Diagnostic Aids
5	Observe the emission related DTC portion of the I/M System Status display with a scan tool. Does the scan tool indicate any emission related DTCs set?	Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK

Inspection/Maintenance (I/M) Exhaust Gas Recirculation (EGR) System Set Procedure

The purpose of this procedure is to satisfy the enable criteria necessary to execute an Inspection/Maintenance (I/M) system monitor for the misfire monitoring system. The system monitor is comprised of the test results from one or more DTCs. This procedure may be used to set the Misfire Monitoring I/M System Status display on the scan tool to YES. The Misfire Monitoring I/M System Status display indicates whether or not the control module has completed the system monitor. The system monitor completes when either all DTCs comprising the monitor run and pass, or any DTC comprising the monitor illuminates the malfunction indicator lamp (MIL). If one of the DTCs comprising the monitor is set and the MIL is not illuminated, the necessary trips are required to illuminate the MIL before the monitor will complete. Once the monitor completes, the Misfire Monitoring I/M System Status display will be updated to YES.

The engine coolant temperature (ECT) is between 57-104°C (133-219°F).

If there is an impending failure, the system may require more time than was allotted in the system set procedure. If any DTCs do not run and the DTC is set, review the appropriate scan tool data list and service information. This will give an indication of why the DTCs do not run. Some may abort due to changes in the conditions while running. For example, changes in engine load, such as a cooling fan or A/C compressor clutch turning ON, may cause a DTC to abort. If the Misfire Monitoring I/M System Status does not update to YES, the procedure can be repeated until a YES status is achieved.

Step	Action	Values	Yes	No
1	Did you perform the Inspection/Maintenance (I/M) System Check?		Go to Step 2	Go to Inspection/Maintenance (I/M) System Check
2	Ensure the vehicle is within the Conditions for Running specified in the supporting text. Set the vehicle parking brake. Verify the transmission is in PARK for automatic transmissions and NEUTRAL for manual transmissions. Turn OFF all of the accessories, e.g., A/C, blower fan, etc. Start and allow the engine to idle for the specified time. Did the Misfire Monitoring I/M System Status update to YES?	2 minutes	Go to Step 5	Go to Step 3
3	Observe the DTC information with a scan tool. Does the scan tool indicate any failed DTCs?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	Go to Step 4
4	Refer to the Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run in order to update the Misfire Monitoring I/M System Status to YES. Observe the Not Ran Since Code Cleared parameter with a scan tool. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the Specific DTC menu of the scan tool. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC. Repeat numbers 4 and 5 of this step for any additional required DTCs that have not run. Observe the I/M System Status with a scan tool. Did the Misfire Monitoring System Status update to YES?		Go to Step 5	Go to Diagnostic Aids
5	Observe the emission related DTC portion of the I/M System Status with a scan tool. Does the scan tool indicate any emission related DTCs set?		Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK

Inspection/Maintenance (I/M) Misfire Monitoring System Set Procedure

The fuel manager/filter assembly consists of the fuel heater, the water-in-fuel sensor, and a filter. The filter contains the coalescer, the device that combines small droplets of water into larger ones, and the filter/separator.

As the fuel enters the filter, the fuel passes through the fuel heater. The heater contains a thermostatic switch that opens or closes to turn the heater OFF or ON, depending on the temperature of the fuel.

The fuel then passes through the filter and the water coalescer, where the droplets of water in the fuel combine into larger drops that fall into the water reservoir in the filter. When fuel flows from the fuel manager/filter assembly to the injection pump, the fuel is clean and free of water.

The fuel heater is operated by a built-in thermostatic switch. The thermostatic switch completes the circuit for the fuel heater element when the thermostatic switch senses a temperature below 15.4°C (59.8°F).

The number below refers to the step number on the diagnostic table.

5: This steps checks for a thermostatic switch that completes the circuit.

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics
1	Does the Water In Fuel lamp operate properly?		Go to Step 2	Go to Water-in-Fuel Lamp Always On in Instrument Panel, Gages, and Console
2	Disconnect the fuel heater harness connector from the top of the fuel filter/heater element housing. Turn ON the ignition with the engine OFF. Probe the fuel heater ignition 1 voltage circuit with a test lamp connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems. Does the test lamp illuminate?		Go to Step 3	Go to Step 6
3	Probe the fuel heater ground circuit at the fuel filter/heater element housing with a test lamp connected to B+. Refer to Troubleshooting with a Test Lamp in Wiring Systems. Does the test lamp illuminate?		Go to Step 4	Go to Step 8
4	Remove the fuel filter from the fuel filter/heater element housing. Test the ignition 1 voltage circuit and the ground circuit for an open in the fuel filter/heater element housing. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems. Did either circuit test open?		Go to Step 9	Go to Step 5
5	Remove the fuel filter/heater element housing from the vehicle. Connect the ignition 1 voltage circuit of the fuel heater to battery voltage source and connect the ground circuit of the fuel heater to the ground of the voltage source. Cool the sensor part of the fuel heater with ice. Observe the heating element. Does the thermostatic switch turn ON when the temperature is within the specified range?	8.4 to +15.4°C (+16.9 to +59.8°F)	Go to Step 11	Go to Step 10
6	Repair the open in the ignition 1 voltage circuit between the fuel filter/heater element housing and the fuse. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?		Go to Step 11
7	Repair the short to ground on the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?		Go to Step 11
8	Repair the open in the ground circuit between the fuel filter/heater element housing and chassis ground. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair?		Go to Step 11
9	Replace the fuel filter/heater element housing. Refer to Fuel Filter/Heater Element Housing Replacement . Did you complete the replacement?		Go to Step 11
10	Replace the fuel heater. Refer to Fuel Filter/Heater Element Housing Replacement . Did you complete the replacement?		Go to Step 11
11	Operate the vehicle under which the problem was noted. Does the system operate properly?		System OK	Go to Step 1

Fuel Heater Inoperative

The fuel filter/heater element housing consists of the fuel heater, the water-in-fuel sensor, and a filter.

As fuel enters the fuel filter/heater element housing, it first passes though the fuel heater. The heater contains a thermostatic switch that turns the heater ON and OFF, depending on the temperature of the fuel. When the temperature is below 8°C (46°F), the heater is turned ON. When the temperature is above 15°C (59°F), the heater is turned OFF.

The fuel then passes through the fuel filter and the water separator, where the droplets of water combine into larger drops, then fall into the water reservoir located in the bottom of the filter.

When fuel flows from the fuel filter/heater element housing to the fuel injection pump, the fuel is clean and free of water.

The numbers below refer to the step numbers on the diagnostic table.

2: This step tests for a fuel heater thermostatic switch that is stuck ON.
3: This steps tests for a thermostatic switch that completes the circuit.

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics
1	Does the Water In Fuel lamp operate properly?		Go to Step 2	Go to Water-in-Fuel Lamp Always On in Instrument Panel, Gages, and Console
2	Remove the fuel filter/heater element housing from the vehicle. Refer to Fuel Filter/Heater Element Housing Replacement . With the fuel filter/heater element housing at room temperature, above 15°C (59°F), connect a DMM between the fuel heater ground circuit and the fuel heater voltage supply circuit. Does the DMM display the specified value?		Go to Step 3	Go to Step 4
3	IMPORTANT: The fuel filter/heater element housing must be cooled to below 8°C (46°F) before the thermostatic switch will turn ON. Cool the fuel filter/heater element housing. Connect the fuel heater voltage supply circuit to battery voltage, and the fuel heater ground circuit to a good ground. Observe the heating element. Does the thermostatic switch turn ON and heat the element when the temperature is within the specified range?	8-15°C (46-59°F)	Go to Step 5	Go to Step 4
4	Replace the fuel filter/heater element housing. Refer to Fuel Filter/Heater Element Housing Replacement . Did you complete the replacement?		Go to Step 5
5	Operate the vehicle under which the condition was noted. Does the system operate properly?		System OK	Go to Step 1

IMPORTANT
The fuel filter/heater element housing must be cooled to below 8°C (46°F) before the thermostatic switch will turn ON.

Fuel Heater Always On

Engine Controls - 6.6l (Troubleshooting & Diagnosis) Chevrolet Cab & Chassis Silverado 3500

Important Preliminary Inspections Before Starting

Visual and Physical Inspection

Verify Customer's Concern

Intermittent Conditions

Hard Start

Surges/Chuggles

Lack of Power, Sluggishness, or Sponginess

Fuel Knock/Combustion Noise

Hesitation, Sag, Stumble

Cuts Out, Misses

Poor Fuel Economy

Rough, Unstable, or Incorrect Idle and Stalling

Excessive Smoke (Gray or Blue)

Excessive Smoke (White)

Excessive Smoke (Black)

Circuit Description

MIL Operation

Test Description

Diagnostic Aids

Fuel Pressure Regulator Diagnosis

Scheme 217

Scheme 218

Scheme 219

Fuel System Description

High Pressure System

Return System

Fuel Leaks

Supply System

Fuel Tank Leak Test

Leak Check Procedure

Contaminants-In-Fuel Diagnosis

Description

Conditions for Updating the I/M System Status

Monitored Emission Control Systems

Inspection/Maintenance (I/M) System DTC Table

Conditions for Running

More articles — Engine Performance

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