Engine Control System & Fuel System - 6.6l (Lbz and Lly) - Troubleshooting & Diagnosis Chevrolet Chevy Express H1500

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Symptoms Description

Symptoms covers conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under Additional Symptoms Testing. Perform the Symptoms Testing before using the Additional Symptoms Testing.

Symptoms Verification

Before using the Symptom tables, perform the following inspections

1. Ensure that the engine control module (ECM) and malfunction indicator lamp (MIL) are operating correctly.
2. Ensure that there are no DTCs that are stored.
3. Ensure that the scan tool data is within a normal operating range. Refer to «Scan Tool Data List (Engine Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-engine-control) or «Scan Tool Data List (Glow Plug Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-glow-plug) .
4. Verify the customer concern.
5. Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition.

Identifying Intermittent Conditions

Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movements of a component. Refer to the following for a list of issues that may cause an intermittent condition

1. Moisture and water intrusion in connectors, terminals, and components
2. Incomplete connector mating
3. Poor terminal contact
4. High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component.
5. Harness that is too short or tight
6. Wire insulation that is chaffed or cut
7. High or low ambient temperature
8. High or low engine coolant temperatures
9. High underhood temperatures
10. Heat build up in component or circuit due to circuit resistance, poor terminal contact, or high electrical load
11. High or low system voltage
12. High vehicle load conditions
13. Rough road surfaces
14. Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge
15. Incorrect installation of aftermarket, add on accessories

Visual/Physical Check

1. Ensure that the control module grounds are clean, tight, and correctly located. Refer to «Power and Grounding Schematic Icons»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-introduction__power-and-grounding-schematic-icons) and «Power and Grounding Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/electrical-component-locations/#wiring-systems-and-power-management-component-locator-power-ground-and-splice-pack-connector-end-views) .
2. Ensure that the air filter is clean and free from restrictions.
3. Ensure that there is no water intrusion in connectors terminals and components.
4. Inspect the air intake ducts for the following conditions: Collapsed Damaged areas Looseness Incorrect installation Leaking
5. Inspect for air leaks at the throttle body mounting area, the MAF sensor and intake manifold sealing surfaces.
6. Inspect the wiring harness for the following conditions: Poor connections Pinches Cuts
7. Inspect for loose, damaged, unseated, or missing sensors/components.
8. Inspect the terminals for corrosion and correct contact.

Symptoms Testing

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

1. Test for the following conditions: The sensor systems for the following: Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to «Mass Airflow Sensor/Intake Air Temperature Sensor Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . 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 Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure parameters. If the pressure difference is more than 2 MPa, a fuel control issue may exist. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) . Inspect the CKP sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement, the reluctor wheel retaining bolts are loose. Inspect the engine coolant temperature (ECT) sensor. Use the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself. The Fuel System for the following: 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»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect the fuel system for a plugged fuel filter, high vacuum, air in the fuel system, etc. Refer to «Fuel System Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect for air in the fuel system. Refer to «Fuel System Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect for external fuel leaks. Refer to «Fuel Leak Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect for low fuel pressure. Command the fuel pressure to 180 MPa with a scan tool while the engine is at idle. If 180 MPa is not achieved, perform «Fuel System Diagnosis - High Pressure Side»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . 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»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect the fuel supply system vacuum while the problem exists. Refer to «Fuel System Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect the fuel quality. Refer to «Contaminants-in-Fuel Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__contaminants-in-fuel-diagnosis) and «Fuel System Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . Observe the actual verses desired fuel rail pressure with a scan tool, with the engine idling. Inspect the engine speed signal circuit for high resistance. If the ECM or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to «Fuel Injector Flow Rate Programming»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . Inspect for restricted or plugged fuel injectors. Refer to «Fuel Injector Balance Test with Tech 2 (Automatic Transmission)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) or «Fuel Injector Balance Test with Tech 2 (Manual Transmission)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-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»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__fuel-pressure-regulator-diagnosis) . Inspect the fuel tank cap vent for proper operation. Engine mechanical for the following. Improper valve timing Bent pushrods Worn rocker arms-Refer to «Valve Rocker Arm and Shaft Cleaning and Inspection»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-4-of-5__valve-rocker-arm-and-shaft-cleaning) . Low engine compression-Refer to «Engine Compression Test»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5__engine-compression-test) . Broken or weak valve springs Worn camshaft lobes-Refer to «Camshaft and Bearings Cleaning and Inspection»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-4-of-5) . Excessive oil in the combustion chamber-Leaking valve seals-Refer to «Oil Consumption Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5__oil-consumption-diagnosis) .
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.

Additional Symptoms Tests

Hard Start

1. Verify that the ECT has not shifted in value. Refer to «Temperature Versus Resistance (ECT Sensors)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-ect-sensors) or «Temperature Versus Resistance (Fuel Temperature Sensor)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-fuel-temperature-sensor) or «Temperature Versus Resistance (IAT Sensor 2)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-iat-sensor-2) or «Temperature Versus Resistance (IAT Sensor 1)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-iat-sensor-1) .
2. Inspect for a slow cranking speed. Refer to «Symptoms - Engine Electrical»(/chevrolet/chevy-express-h1500/2003-2012/remont/charging-system/#battery-charging-system-and-starting-system__symptoms-engine-electrical) .
3. Verify the engine electrical system for correct operation. Refer to «Symptoms - Engine Electrical»(/chevrolet/chevy-express-h1500/2003-2012/remont/charging-system/#battery-charging-system-and-starting-system__symptoms-engine-electrical) .
4. Verify that the driver is using the correct starting procedure as described in the owners manual.
5. Inspect for a restriction in turbocharger inlet duct.
6. Inspect for a restriction or a leak in the intake manifolds.
7. Inspect the exhaust system for a possible restriction. Refer to «Restricted Exhaust»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) .
8. Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor.

Hesitation, Sag, Stumble

1. Test the generator. Refer to «Symptoms - Engine Electrical»(/chevrolet/chevy-express-h1500/2003-2012/remont/charging-system/#battery-charging-system-and-starting-system__symptoms-engine-electrical) . Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts.
2. Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor.

Poor Fuel Economy

1. Heavy loads being carried or towed
2. Acceleration rate too much or too often
3. Inspect the brake system for brake drag.
4. Inspect the tires for the correct air pressure.
5. Inspect for incorrect operation of the speedometer.
6. Inspect for an air leak in the charge air cooler. Refer to «Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) or «Charge Air Cooler Diagnosis (Full System Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .
7. Inspect the air conditioning system for proper operation.
8. Suggest to the owner to fill the fuel tank and inspect the fuel economy.
9. Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual.
10. Verify that the ECT has not shifted in value. Refer to «Temperature Versus Resistance (ECT Sensors)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-ect-sensors) or «Temperature Versus Resistance (Fuel Temperature Sensor)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-fuel-temperature-sensor) or «Temperature Versus Resistance (IAT Sensor 2)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-iat-sensor-2) or «Temperature Versus Resistance (IAT Sensor 1)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__temperature-versus-resistance-iat-sensor-1) .

Lack of Power, Hesitation, or Cut Out

1. Inspect the engine electrical system for correct operation. Refer to «Symptoms - Engine Electrical»(/chevrolet/chevy-express-h1500/2003-2012/remont/charging-system/#battery-charging-system-and-starting-system__symptoms-engine-electrical) .
2. Inspect for auxiliary fuel filters. Refer to «Fuel Injection Line Routing Diagram»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) for proper fuel filter locations. Aftermarket fuel filters may restrict fuel flow.
3. Compare the vehicle with a similar unit. Ensure the vehicle has an actual problem.
4. Inspect for a proper transmission operation.
5. Inspect the engine oil level and quality.
6. Inspect for an air leak in the charge air cooler. Refer to «Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) or «Charge Air Cooler Diagnosis (Full System Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .
7. Inspect for a worn or damaged turbo charger turbine wheel, shaft or compressor wheel.
8. Inspect for a restriction in the charge air cooler.
9. Inspect for a skewed mass air flow (MAF) sensor. Refer to Diagnostic Aids in «DTC P0101»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-dtc-p0016-to-dtc-p0341) .
10. Inspect that the exhaust gas recirculation (EGR) valve is fully closing. Remove the EGR valve and visually inspect that there is no light seen between the valves and the valve seats.
11. Ensure that the EGR valve does not bind when manually moving the valve.
12. Inspect the torque converter clutch (TCC) operation.
13. Inspect the air conditioning system for proper operation. Refer to «Air Conditioning (A/C) System Performance Test»(/chevrolet/chevy-express-h1500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-ac-system-performance-test) .

Rough, Unstable, or Incorrect Idle and Stalling

1. Inspect the engine mounts. Refer to «Engine Mount Inspection»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-2-of-5__engine-mount-inspection) .
2. Inspect the intake and exhaust manifolds for casting flash.
3. The exhaust system for damaged or collapsed pipes
4. The exhaust manifold for a collapsed inner wall
5. The mufflers for heat distress or possible internal failure
6. 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.
7. Inspect the park neutral position (PNP) switch circuit.

Surges/Chuggles

1. Ensure the driver understands the torque converter clutch (TCC) operation.
2. Ensure the driver understands the A/C compressor operation.
3. 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.

Fuel Knock/Combustion Noise

1. Inspect for obvious overheating problems. Refer to «Engine Overheating»(/chevrolet/chevy-express-h1500/2003-2012/remont/cooling-system-mechanical/#engine-cooling-system__engine-overheating) .
2. Inspect for a low engine coolant level.
3. Inspect for any restricted air flow through the radiator. Refer to «Radiator Cleaning»(/chevrolet/chevy-express-h1500/2003-2012/remont/cooling-system-mechanical/#engine-cooling-system__radiator-cleaning) .
4. Inspect for a malfunctioning or incorrect thermostat.
5. Inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Excessive Smoke (Black)

1. Normal Operation During light to moderate acceleration there should be no black smoke. During the 2-3 hard accelerations after normal light load driving there may be some black smoke momentarily but should not last for more than 5 seconds. During hard acceleration there may always be a very faint puff of black smoke.
2. Abnormal Operation Black smoke during light to moderate acceleration Heavy black smoke during hard acceleration that lasts for more than 5 seconds Heavy black smoke during every hard acceleration and/or during transmission shift transitions Inspect for an air leak in the charge air cooler or the air ducts between the turbocharger and the intake manifold. Refer to «Charge Air Cooler Diagnosis (Charge Air Cooler Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) or «Charge Air Cooler Diagnosis (Full System Air Leak Test)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . Inspect for a restriction in the turbocharger charge air cooler. Inspect for a restriction in the intake manifold. Inspect that the EGR valve is fully closing. Remove the EGR valve and visually inspect that there is no light seen between the valves and the valve seats. Ensure that the EGR valve does not bind when manually moving the valve. Inspect for excessive oil entering the combustion chamber. Refer to «Oil Consumption Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5__oil-consumption-diagnosis) .

Excessive Smoke (White)

1. 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»(/chevrolet/chevy-express-h1500/2003-2012/remont/cooling-system-mechanical/#engine-cooling-system__loss-of-coolant) .
2. If excessive smoke is present, inspect for a stuck open fuel injector by performing the following procedure: Disconnect the CKP sensor. Remove the glow plugs. Refer to «Glow Plug Replacement - Bank 1»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) and «Glow Plug Replacement - Bank 2»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-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.
3. If the ECM glow plug control module (GPCM) or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to «Fuel Injector Flow Rate Programming»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
4. Inspect the fuel injectors. Refer to «Fuel Injector Balance Test with Tech 2 (Automatic Transmission)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) or «Fuel Injector Balance Test with Tech 2 (Manual Transmission)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit/System Description

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

The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The engine control module (ECM) performs a self test for the MIL lamp and its circuitry by commanding the MIL ON and OFF every time the engine is started. The ECM monitors the MIL control circuit for conditions that are incorrect for the commanded states of the MIL.

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.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

1. «Engine Controls Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Engine Controls Component Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
3. «Engine Control Module Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

1. «Scan Tool Data List (Engine Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-engine-control) or «Scan Tool Data List (Glow Plug Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-glow-plug)
2. «Scan Tool Data Definitions»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-definitions)
3. «Scan Tool Output Controls»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-output-controls)

Circuit/System Verification

The MIL should turn ON and OFF when commanded with a scan tool.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the instrument panel cluster (IPC).
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the IPC.
3. Connect a test lamp between the control circuit and the ignition circuit.
4. Command the MIL On and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
5. If all circuits test normal, replace the IPC.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM and IPC replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

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.

Diagnostic Aids

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

1. 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/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-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.
2. The correct cranking speed is 100 RPM cold and 180 RPM hot.
3. A basic engine problem
4. Low engine coolant may cause the engine to shut down.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

1. «Engine Control Module Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Engine Controls Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

1. «Scan Tool Data List (Engine Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-engine-control) or «Scan Tool Data List (Glow Plug Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-glow-plug)
2. «Scan Tool Data Definitions»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-definitions)

Special Tools Required

CH-48027 Vacuum Gage. See Special Tools .

1. If DTCs P0090, P0191, P0193, P0335, P0336, P0340, P0602, P0603, P0604, P0606, P0642, P0643, P064C, P0698, P0699, P2510 are set, diagnose those DTCs first.
2. The engine starts and runs. If the engine does not start and run perform the Circuit/System Testing.

1. Inspect for the following conditions: Fuel smell or leak-Refer to «Fuel Leak Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . A plugged air filter collapsed air intake duct-Refer to «Air Cleaner Element Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . A restricted exhaust system-Refer to «Symptoms - Engine Exhaust»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system__symptoms-engine-exhaust) . Contaminants in fuel-Refer to «Contaminants-in-Fuel Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__contaminants-in-fuel-diagnosis) .
2. Install the CH-48027 to the fuel rail service port and crank the engine. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . If more than 5 inches Hg of vacuum was present during cranking, replace the fuel filter and inspect the fuel system restrictions.
3. Perform the Engine Compression Test. Refer to «Engine Compression Test»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5__engine-compression-test) . IMPORTANT: During the replacement of the injectors, inspect the inlet and outlet fittings for corrosion or contamination. Refer to «Contaminants-in-Fuel Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__contaminants-in-fuel-diagnosis) . If any fuel vapor was emitted during the engine compression test, replace the affected fuel injector. Refer to «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right) .
4. Assemble all disconnected components. Prime the fuel system to at least 10 psi. Attempt to start the engine. If the engine does start, refer to «Fuel System Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . If the engine does not start, refer to «Fuel System Diagnosis - High Pressure Side»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Injector Replacement (Left) or Fuel Injector Replacement (Right)

Repair Verification

The engine starts and runs.

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

Fuel Pump Electrical Circuit Diagnosis

An electric fuel pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel pump is part of the diesel fuel conditioning module (DFCM) assembly. The fuel pump is powered by the fuel pump relay. The fuel pump relay is controlled by the engine control module (ECM). The ECM enables the fuel pump when the ignition is turned ON, and will continue to run for two minutes, or until the engine starts. If the engine does not start due to low fuel pressure, and the ignition is left in the ON position, the pump will run for up to two minutes or until the ignition is turned OFF. The ECM will also turn OFF the fuel pump if incorrect voltage is detected on the control circuit. The ECM will need to be powered down with a key cycle during diagnosis or after repairs, before it will command the fuel pump ON again.

The following conditions may cause the fuel pump fuse to open

1. A faulty fuse
2. An intermittent short to ground in the supply voltage circuit of the fuel pump
3. The fuel pump has an intermittent internal condition

Schematic Reference

Engine Controls Schematics

Connector End View Reference

1. «Inline Harness Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-starting-point-and-in-line-harness-connector-end-views)
2. «Engine Controls Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

1. «Scan Tool Data List (Engine Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-engine-control) or «Scan Tool Data List (Glow Plug Control Module)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-list-glow-plug)
2. «Scan Tool Data Definitions»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-data-definitions)
3. «Scan Tool Output Controls»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-1-of-2__scan-tool-output-controls)

Special Tools Required

CH-48027 Digital Pressure Gage. See Special Tools .

Install the CH-48027 to the fuel system service port on the right front side of the engine. See Special Tools . Command the fuel pump ON with a scan tool and observe the fuel pressure gage. You should either hear or feel the relay click and the fuel pump should turn ON and OFF with each command. Fuel pressure should be a minimum of 69 kPa (10 psi) with the fuel pump running.

1. Inspect the fuel pump fuse. If the fuel pump fuse is open, test the battery positive voltage circuit and the fuel pump supply voltage circuit for a short to ground or a faulty fuel pump.
2. Turn ON the ignition, with the engine OFF.
3. Command the fuel pump ON and OFF with a scan tool. The fuel pump relay should click and turn ON and OFF with each command. If the fuel pump operates continuously, test for a faulty relay or a short to voltage in the fuel pump supply voltage circuit. If the fuel pump does not turn ON and OFF, replace the fuel pump relay.
4. Probe the battery positive voltage circuit of the fuel pump relay with a test lamp that is connected to a good ground. If the test lamp does not illuminate, repair the open in the battery positive voltage circuit.
5. Connect a fused jumper wire between the battery positive voltage circuit and the supply voltage circuit of the fuel pump relay. If the fuel pump operates, test for an intermittent and for a poor connection at the fuel pump relay, or a faulty fuel pump relay. If the fuel pump does not operate, test for an open or high resistance in the supply voltage circuit, or ground circuit of the fuel pump. If all circuits test normal and the fuel pump relay operates properly, replace the DFCM housing containing the fuel pump.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Primary Fuel Filter Replacement

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.

1. 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.
2. Start and idle the engine.
3. 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
4. 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/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .

Scheme 313

Scheme 314

Scheme 315

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Fuel is drawn by the fuel injection pump through a pre-filter screen in the tank. Fuel flows to the diesel fuel conditioning module (DFCM), which combines a water separator, an electric fuel prime pump, fuel heater element, and a filter element. The fuel is then delivered to a second screw on fuel filter and the high-pressure pump. An integrated electric fuel prime pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The mechanical fuel injection pump at the front of the engine valley includes the fuel supply pump and the high-pressure pump.

High Pressure System

The much larger section of the fuel injection 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 fuel flows to the left fuel rail. A balance pipe from the center of the left fuel rail then feeds the right fuel rail. Each fuel rail supplies one bank of 4 fuel injectors. The fuel rail pressure (FRP) sensor is mounted in the right fuel rail.

Return System

Fuel is used to cool and lubricate the fuel injectors and fuel injection pump. The fuel return system is designed to return this fuel to the fuel tank. If the high side fuel pressure becomes excessive, the fuel rail pressure relief valve releases the fuel into the fuel return system. The return fuel travels through the diesel fuel conditioning module and the fuel cooler, then to the fuel tank.

A Cranks But Will Not Run or Hard Start symptom may exist if air is being drawn into the fuel injection system due to the following conditions

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

Special Tools Required

1. CH-48027 Digital Pressure Gage. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
2. J 35555 Metal MityVac. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
3. EN-47969 Fuel Supply Diagnostic Hose. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
4. J 44581 Fuel Line Disconnect Tool. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

Observe the Actual Fuel Rail Pressure parameter with a scan tool. During engine cranking, the pressure should be at least 10 MPa. With the engine running at idle the pressure should be close to the Desired Fuel Rail Pressure. As the engine RPM's increase, the Desired Fuel Rail Pressure and the Actual Fuel Rail Pressure should closely match each other.

1. Remove the engine cover. Refer to «Engine Cover Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
2. Clean all of the fuel lines between the fuel injection pump and the fuel injectors using brake cleaning solvent, and let dry.
3. Install the CH-48027 to the fuel system service port on the right front side of the engine. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
4. Command the fuel pump ON with a scan tool and observe the fuel pressure gage to ensure that fuel pressure is present. Visually inspect the engine and chassis for leaks or damage to the fuel hoses, fuel lines, and fuel system components. Repair any leaks or replace any components found to be damaged or leaking. If the fuel pump did not run and fuel pressure was not observed, refer to «Fuel Pump Electrical Circuit Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) . If the fuel pump did run and fuel pressure was not observed, inspect the fuel feed line for a vacuum leak between the DFCM and the fuel tank sender.
5. If leaks or damage were not found on the fuel system, turn OFF the fuel pump and disconnect the fuel supply line at the engine. Refer to «Metal Collar Quick Connect Fitting Service»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__metal-collar-quick-connect-fitting-service) .
6. Cap off the fuel supply pipe on the engine with a rubber plug and a clamp.
7. Remove the fuel pump relay. Crank the engine and observe the CH-48027 to see if the fuel injection pump is creating at least 10 inches Hg of vacuum. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . If vacuum is present during cranking but bleeds off rapidly, repair the leak in the fuel supply line. If vacuum is not present during cranking, replace the fuel injection pump. Refer to «Fuel Injection Pump Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
8. Remove the rubber plug from the fuel supply line and install the EN-47969 . See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . Create a vertical loop in the hose to observe the incoming fuel for air bubbles. Command the Fuel Pump ON with a scan tool and prime the fuel system until all air has been purged. Start and run the engine for at least 10 minutes to allow the fuel system to stabilize. At a stabilized idle, observe the fuel entering the EN-47969 for air bubbles. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . If air bubbles were observed entering the transparent hose, test the fuel sender for leaks. Refer to «Fuel Sender Assembly Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
9. Install the fuel sender, fuel tank, and all fuel system connections and components that were previously disconnected. Leave the EN-47969 connected to the fuel supply line. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . Command the fuel pump ON with a scan tool and prime the fuel system until all air is purged. Start and run the engine, while observing the fuel entering the transparent hose. If air bubbles are still present, refer to Diagnostic Aids. If no air bubbles are present, remove the EN-47969 and run the engine to ensure no fuel leaks exist. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fuel Injection Pump Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Fuel Sender Assembly Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Fuel is used to cool and lubricate the fuel injectors and fuel injection pump. The fuel return system is designed to return this fuel to the fuel tank. If the high side fuel pressure becomes excessive, the fuel rail pressure relief valve releases the fuel into the fuel return system. The return fuel travels through the diesel fuel conditioning module and the fuel cooler, then to the fuel tank.

Bent or pinched fuel return lines may cause an external fuel leak or engine performance concerns.

Special Tools Required

J 44581 Fuel Line Disconnect Tool. See Special Tools .

Inspect the fuel return hoses and lines on the engine and chassis for any external fuel leaks.

1. Disconnect the fuel return line at the engine. Refer to «Metal Collar Quick Connect Fitting Service»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__metal-collar-quick-connect-fitting-service) .
2. Remove the fuel filler cap.
3. Apply 1 psi of air into the fuel return at the engine and listen for air flowing from the tank at the filler tube.
4. If air flow was not detected, disconnect the fuel return line at the fuel sender and retest using 1 psi of air. If air flow was present, replace the fuel sender assembly. If no air flow was present, inspect for a restricted or a damaged fuel return line. Repair or replace the fuel return line.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fuel Return Pipe Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-return-pipe-replacement)
2. «Fuel Sender Assembly Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit System Testing

1. Remove the air cleaner assemble and engine cover. Refer to «Air Cleaner Assembly Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) and «Engine Cover Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
2. Clean all of the fuel lines between the fuel injection pump and the fuel injectors using brake cleaning solvent, and let dry.
3. Add 8 ounces of oil dye to the fuel tank.
4. Start and idle the engine for 3-5 minutes.
5. Command the fuel pressure control to 180 MPa (23,206 psi) with a scan tool.
6. 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. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . Tighten or replace any leaking lines or components. Refer to the following: «Fastener Tightening Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fastener-tightening-specifications) «Fuel Injection Line Routing Diagram»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Injection Fuel Return Pipe Replacement - Left Side»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Injection Fuel Return Pipe Replacement - Right Side»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Return Pipe Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-return-pipe-replacement) «Fuel Injection Fuel Rail Assembly Replacement - Bank 1»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Injection Fuel Rail Assembly Replacement - Bank 2»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Injection Pump Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right)
7. A fuel leak may be caused by restricted return fuel lines. Refer to «Fuel Return System Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The fuel injection pump at the front of the engine valley includes a fuel supply pump and a high-pressure pump. Fuel is drawn by the fuel supply pump from the primary fuel tank and delivered to the high-pressure pump. The pump is engine-driven by the camshaft gear. High pressure fuel is regulated by the fuel pressure regulator mounted on the fuel injection pump. From the high-pressure pump, the fuel moves to the left and right fuel rails through high pressure metal lines. Each fuel rail distributes high pressure fuel to one bank of 4 fuel injectors. The fuel pressure relief valve is location on the left rail, and relieves excessive fuel pressure which returns to the fuel tank.

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.

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

Special Tools Required

1. J 45873 Fuel Return Volume Test Kit. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
2. J-45873-30 Injector Flow Test Adapter. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

With the engine running at idle the Actual Fuel Pressure should be close to the Desired Fuel Rail Pressure. During engine cranking the Actual Fuel Pressure should be at least 10 MPa. Inspect the fuel return hoses and lines for external leaks or damage.

1. Remove the fuel pressure relief valve return hose and plug the hose to prevent fuel leakage.
2. Install a section of rubber fuel hose on the fuel pressure relief valve connection and place loose end of hose into a clean fuel container. IMPORTANT: Fuel that is contaminated with gasoline may cause permanent damage to the fuel pressure relief valve. Refer to «Contaminants-in-Fuel Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__contaminants-in-fuel-diagnosis) . If the engine cranks but does not start, crank engine for 15 seconds. Observe for fuel leaking from fuel pressure relief valve. If fuel leaks from the fuel pressure relief valve, replace the pressure relief valve. Refer to «Fuel Pressure Relief Valve Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . If the engine starts and runs, idle the engine while commanding the fuel rail pressure to 180 MPa with a scan tool. Observe for fuel leaking from fuel pressure relief valve. If fuel leaks from the fuel pressure relief valve, replace the pressure relief valve. Refer to «Fuel Pressure Relief Valve Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
3. Remove the fuel return hose from the fuel injectors of the right cylinder bank. Refer to «Fuel Injection Fuel Return Pipe Replacement - Right Side»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
4. Connect the yellow hoses from the J 45873 to the J-45873-30 . See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
5. Connect the J-45873-30 with yellow hoses to each fuel injector return port of the right cylinder bank, and install the retaining clips. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
6. Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical order. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
7. Connect the fuel return hoses to the J-45873-30 to prevent leakage. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . If the engine starts and runs, idle the engine until fuel start dripping into all the graduated cylinders and yellow hoses are full of fuel. IMPORTANT: The engine cranking speed must be more than 150 RPM during the cranking portion of this test. If the engine does not start, 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.
8. Elevate the 4 yellow hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container.
9. Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical order. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . If the engine starts and runs, idle the engine for 15 seconds. If the engine does not start, crank the engine for 15 seconds.
10. Measure the quantity of fuel in each of the graduated cylinders. Refer to «Fuel System Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) for the desired quantities. If high return flows were recorded, replace those fuel injectors that had high return flow and retest the fuel return flow, referring to «Fuel System Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . Replace any additional high return flow injectors and proceed to the next number step.
11. Remove the fuel return pipes from the fuel injectors of the left cylinder bank and repeat the fuel return flow test previously preformed on the right cylinder bank. If high return flows were recorded, replace those fuel injectors that had high return flow and retest the fuel return flow, referring to «Fuel System Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) . Replace any additional high return flow injectors and proceed to the next number step.
12. Start and idle the engine. You may have to prime the fuel system before the engine will start. If the engine does not start after priming the fuel system, replace the fuel injection pump. Refer to «Fuel Injection Pump Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
13. Command the fuel pressure control to 180 MPa with a scan tool. The fuel pressure should be able to reach 145 MPa when commanded. If the fuel pressure is less than the specified value, inspect for debris in the inlet of the left fuel rail. No debris should be present. If debris is found in the inlet of the left fuel rail, replace the left fuel rail and the fuel injection pump. If no debris is found in the inlet of the left fuel rail, replace the fuel injection pump.
14. Install and connect all fuel system components that were previously removed or disconnected. IMPORTANT: The fuel system may have to be primed before starting the engine.
15. Operate the vehicle in order to verify the repairs.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fuel Injection Pump Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Fuel Pressure Relief Valve Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
3. «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The fuel injector balance test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical DTCs. This test uses the Balance Rate and Cylinder Power Balance test to identify cylinders that are not producing the designed power output. The balance rate adjustments are utilized by the engine control module (ECM) only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. The balance rates will change depending on if the transmission is in Neutral or Drive. During the Cylinder Power Balance portion of the test, the ECM turns OFF individual injectors while the engine is running. The ECM adjusts for the drop in engine RPM during cancellation and may not change on the scan tool display. The lack of power at the cancelled cylinder will feel like a misfiring cylinder or vibration. If a fuel injector is turned OFF and there is a no difference felt when compared to the other cylinders, that cylinder is identified with the concern. If the customer concern 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.

1. 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.
2. A high balance rate may be caused by a fuel injector or compression only if the ECM can control fuel pressure.

1. Start and run the engine until the coolant temperature is more than 82°C (180°F). Turn OFF all accessories.
2. Perform the fuel pressure regulator test, refer to «Fuel Pressure Regulator Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__fuel-pressure-regulator-diagnosis) .
3. Apply the parking brake and hold the brake pedal in the fully applied position. A hissing noise will be noticeable when the brake pedal is fully applied. Place the transmission in Drive and idle the engine for a minimum of 30 seconds. With a scan tool, observe the balancing rates parameters for cylinders 1-8 while the engine is at idle speed. Repeat this procedure with the transmission in the Park or Neutral position. Balance Rates should be between +4 mm 3 and -4mm 3 in Park or Neutral and +6mm 3 and -6mm 3 in Drive.
4. Perform the Cylinder Power Balance Test with a scan tool. During cylinder cancellation a noticeable power difference will feel like a misfiring cylinder or vibration.

Perform the engine compression test. Refer to Engine Compression Test .

1. If the compression indicated any of the cylinders had low compression, refer to «Symptoms - Engine Mechanical»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5) .
2. If the engine did not have low compression on any of the cylinders, replace the fuel injectors on the cylinders that had low cylinder power contribution, high balance rates, or a noise/smoke change during cancellation.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fuel Pressure Regulator Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The fuel injector balance test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical DTCs. This test uses the Balance Rate and Cylinder Power Balance test to identify cylinders that are not producing the designed power output. The balance rate adjustments are utilized by the engine control module (ECM) only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. The balance rates will change depending on if the transmission is in Neutral or Drive. During the Cylinder Power Balance portion of the test, the ECM turns OFF individual injectors while the engine is running. The ECM adjusts for the drop in engine RPM during cancellation and may not change on the scan tool display. The lack of power at the cancelled cylinder will feel like a misfiring cylinder or vibration. If a fuel injector is turned OFF and there is a no difference felt when compared to the other cylinders, that cylinder is identified with the concern. If the customer concern 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 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.

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.

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.

A high balance rate may be caused by a fuel injector or compression only if the ECM can control fuel pressure.

Observe the Balancing Rate parameters with a scan tool. Normal reading should be between +4 mm 3 and -4 mm 3 at idle. With the engine running at idle, the Actual Fuel Rail Pressure should be close to the Desired Fuel Rail Pressure.

If any DTCs other than DTC P0300, P0301-P0308 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

1. Start and run the engine until the ECT is more than 82°C (180°F).
2. Turn OFF all accessories.
3. Perform the fuel pressure regulator test. Refer to «Fuel Pressure Regulator Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis__fuel-pressure-regulator-diagnosis) . If the fuel pressure regulator graph was not normal, replace the fuel pressure regulator. Refer to «Fuel Pressure Regulator Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
4. Place the transmission in Neutral and apply the parking brake.
5. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied.
6. Idle the engine for more than 30 seconds.
7. Record the Balancing Rate Cyl.1-8 parameters from the scan tool while the engine is at idle speed. If at least 5 of the Balancing Rates are more than +4 mm 3 , refer to «Engine Flywheel Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-3-of-5__engine-flywheel-replacement) . If the Balance Rates are not between +4 mm 3 and -4 mm 3 at idle, perform the Cylinder Power Balance Test in Special Functions.
8. Record any cylinders that indicate a different cylinder power contribution and compare the Balance Rates previously recorded with the Cylinder Power Balance results. If the Balance Rates were not high or the Cylinder Power Balance test did not indicated a cylinder with a different power contribution, refer to Diagnostic Aids.
9. Perform the engine compression test. Refer to «Engine Compression Test»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5__engine-compression-test) . If the compression test indicated any of the cylinder had low compression, refer to «Symptoms - Engine Mechanical»(/chevrolet/chevy-express-h1500/2003-2012/remont/mechanical/#engine-mechanical-66l-1-of-5) .
10. If the engine did not have low compression on any of the cylinders, replace the fuel injectors on the cylinders that had poor cylinder power contribution, high balance rates, or a noise/smoke change during cancellation. Refer to «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right) .
11. Operate the vehicle under the conditions in which the concern occurred.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Fuel Pressure Regulator Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)
2. «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right)

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

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

1. Disconnect the battery cables.
2. Drain the fuel tank. Refer to «Fuel Tank Draining»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-tank-draining) .
3. Remove the fuel tank. Refer to «Fuel Tank Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
4. Cap the fuel feed tube and the fuel return tube on the fuel sender.
5. Connect a piece of hose to the filler tube nipple and plug the opposite end.
6. Submerge the tank in water or apply a soap solution to the outside of the tank.
7. 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. Service station tanks may contain fungi that could be pumped into a vehicle during refueling.

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.

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 due to possible engine power loss. It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing.

Water in fuel will also create drivability concerns and loss of engine power. If water is present in the fuel system, the fuel cannot cool and lubricate the components, causing overheating, rust and corrosion. This can result in component failure. Water can enter the fuel system in several ways, either through a contaminated refueling source, or through long term condensation the vehicle fuel tanks.

Like fungi and water, gasoline contamination will cause drivability concerns and a possible hard starting or a no start condition if the overall content is large enough. Gasoline raises the API rating and reduces cooling and lubrication, resulting in possible component failure.

Inspecting for Fuel Contaminants

1. Test the fuel specific gravity and record the results. Refer to «Fuel System Specifications»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2) .
2. Remove the fuel filter and inspect the inside area of the fuel filter for dirt, water deposits, or other debris.
3. Drain the fuel filter into an approved clear container and allow the contents to settle. Observe the container for contaminant separation.
4. Remove the water-in-fuel sensor from the bottom of the fuel filter and inspect inside the filter for rust deposits, dirt, or other debris.
5. If contaminants are present in the fuel or in any of the inspected areas, remove the fuel lines to the injectors and inspect the fuel injector return outlets and feed inlets for rust or corrosion.

1. Replace the fuel injectors if rust or corrosion is present. Refer to «Fuel Injector Replacement (Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-left) or «Fuel Injector Replacement (Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-injector-replacement-right) and «Fuel System Cleaning»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-system-cleaning) .
2. If rust or corrosion was not present in the injectors, but fungi, water or gasoline was present, refer to «Fuel System Cleaning»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__fuel-system-cleaning) and attempt to start and run the engine after procedure is completed.

Circuit Description

The high idle system is used to provide additional engine power when needed for vehicle accessories. The engine control module (ECM) controls the high idle operation based on various sensor inputs and the high idle switch on the instrument console. This system is not activated by temperatures as is the high idle system for warm up, but the rest of the input and operation are the same. For more information on these parameters, refer to Manual High Idle System Description .

If the high idle system is inoperative but the switch circuit works, inspect for the following conditions

1. The high idle switch option is not programmed-Refer to «High Idle Switch Programming»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__high-idle-switch-programming) .
2. There are DTCs set-Diagnose these first.
3. There is a non-DTC fault in one of the following components or systems: The brake switch The clutch switch The vehicle speed sensor

High Idle Switch Diagnosis (with RPO UF3)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Special Tools

1. J 46091 Charge Air Cooler Tester. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
2. J-46091-10 Charge Air Cooler Tester Adapter. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

Charge Air Cooler Outlet Connection (Engine Air Intake COLD Side)

1. Loosen the charge air cooler (CAC) clamp (1) that fastens the right air cooler duct to the intake air heater (2).
2. Remove the right charge air cooler duct (3) from the intake air heater inlet.
3. Install the J 46091-10 pressure adapter to the charge air duct.
4. Use the clamp to secure the adapter to the charge air duct. Tighten: Tighten the clamp to 8 N.m (70 lb in).
5. Secure the safety cable.

Scheme 316

1. Remove the engine cover. Refer to «Engine Cover Replacement»(/chevrolet/chevy-express-h1500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
2. Loosen the right clamp that fastens the left air cooler duct to turbocharger (1).
3. Remove the left charge air cooler inlet duct connector (4) from the turbocharger.
4. Use the clamp to attach the gage couple from the J 46091 to the charge air hose. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . Tighten: Torque the clamp to 8 N.m (70 lb in).
5. Secure the safety cable.
6. Attach the gage/regulator assembly from the J 46091 to the quick disconnect fitting on the gage coupler. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

Leak Test - Air Pressure Application

1. Connect the filtered air supply to the air valve on the gage/regulator assembly.
2. Open the air valve SLOWLY, increasing the air pressure in 34-69 kPa (5-10 psi) increments while listening for air leaks. Continue increasing the air pressure until the gage reads 205 kPa (30 psi).
3. Close the air valve and monitor the gage for 15 seconds. Note any decrease in air pressure.
4. Repeat the test 3 times to verify the results.

Leak Test Fails

If the pressure drop is more than 34 kPa (5 psi) in 15 seconds, the leak test has failed. Perform the following procedure

1. Inspect for air leaks using a pump spray bottle to apply a soapy solution to the pipes/hoses, charge air cooler hose connections, and charge air cooler core. Observe for bubbles.
2. Replace or tighten the affected component as necessary.
3. Retest the CAC system. If no other leaks are found, assemble the vehicle and clear the DTC information with a scan tool.

Leak Test Passes

If the pressure drop is less than 34 kPa (5 psi) in 15 seconds, the leak test passes. Remove the tester by performing the following procedure

1. Slowly bleed the air from the cooler by depressing the relief valve on the adapter plate.
2. Remove the air hose, gage/regulator assembly, and both adapters.
3. Connect the charge air hose to the turbocharger. Tighten: Torque the clamp to 8 N.m (70 lb in).

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Special Tools Required

1. J 46091 Charge Air Cooler Tester. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
2. J-46091-5 Charge Air Cooler Tester Adapter

Charge Air Cooler Inlet Connection (Engine Air Intake Hot Side)

1. Loosen the clamp (1) that fastens the left air cooler duct (4) to the turbocharger.
2. Remove the left charge air cooler inlet duct connector (4) from the turbocharger.
3. Use the clamp to attach the J-46091-3 (1) from the J 46091 to the duct connector (4). See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) . Tighten: Tighten the clamp to 8 N.m (70 lb in).
4. Secure the J 46091 (1) safety cable (2) to a safe location (3). See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .

Turbocharger Exhaust Pipe Connection

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/hoistjack/#general-information) .
2. Remove the catalytic converter. Refer to «Catalytic Converter Replacement (Dual Exhaust - Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) or «Catalytic Converter Replacement (Dual Exhaust - Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) or «Catalytic Converter Replacement (6.6L (LBZ/LLY))»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) .
3. Install the J-46091-15 Adapter with the exhaust pipe clamp to the turbocharger exhaust pipe using the clamp from the catalytic converter.

Air Pressure Application

1. Attach the gage/regulator assembly from the J 46091 to the quick disconnect fitting on the J-46091-15. See «Special Tools»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2__special-tools) .
2. Connect the air supply to the air valve on the gage/regulator assembly.
3. Open the air supply valve slowly, increasing the air pressure in 34-69 kPa (5-10 psi) increments while listening for air leaks.
4. Continue increasing the air pressure until the air valve is fully open.

If the pressure gage reads less than 158 kPa (23 psi) with constant air pressure, and audible air leaks are present, the leak test has failed. Perform the following procedure

1. Inspect for air leaks by listening for excessive hissing sounds.
2. Inspect for air leaks by using a pump spray bottle to apply a soapy solution, while observing for excessive soapy bubbles at all of the following engine locations: Charge air cooler pipes/hoses connections Charge air cooler core EGR valve gaskets EGR valve cooler gaskets Exhaust manifold gaskets Turbocharger gaskets, inlet and outlet connections Intake manifold gaskets
3. Replace the affected gasket or component, as necessary.
4. Retest the engine system. If no other leaks are found, assemble the vehicle and clear the DTC information with a scan tool.

If the pressure gage reads greater than 158 kPa (23 psi) with a constant air pressure, and audible air leaks are not present, the leak test passes. Remove the tester and adapters by performing the following procedure

1. Slowly bleed the air from the cooler by depressing the relief valve on the adapter plate.
2. Remove the air hose, gage/regulator assembly, and both adapters.
3. Connect the charge air hose to the turbocharger.
4. Install the catalytic converter. Refer to «Catalytic Converter Replacement (Dual Exhaust - Left)»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) or «Catalytic Converter Replacement (Dual Exhaust - Right)»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) or or «Catalytic Converter Replacement (6.6L (LBZ/LLY))»(/chevrolet/chevy-express-h1500/2003-2012/remont/exhaust/#engine-exhaust-system) . Tighten: Tighten the clamp to 8 N.m (70 lb in).

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The purpose of the inspection maintenance (I/M) complete system set procedure is to satisfy the enabled 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 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

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the system monitor.
2. The battery has been disconnected or discharged below operating voltage.
3. The control module power or ground has been interrupted.
4. The control module has been reprogrammed.
5. 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

1. Comprehensive component monitoring-Emission related inputs and outputs
2. The EGR system
3. Misfire monitoring

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

Review the I/M system status indicators. All I/M system status indictors should report YES.

1. Repair any DTCs or driveability concerns.
2. Review any service bulletins for software updates that may prevent the required DTCs from running.
3. Perform any reprogramming or repairs indicated by the service bulletins. If more than one system indicates a NO status or did not update to YES, refer to «Inspection/Maintenance (I/M) Complete System Set Procedure»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Inspection/Maintenance (I/M) System DTC Table

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The purpose of the inspection/maintenance (I/M) complete system set procedure is to satisfy the enabled 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 Meeting a Cold Engine

1. The battery voltage is between 11-18 volts.
2. The engine coolant temperature (ECT) is between 57-104°C (133-219°F).
3. The intake air temperature (IAT) is more than 5.25°C (41.5°F).
4. The barometric pressure (BARO) is more than 74 kPa.

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 I/M system status does not update to YES, the procedure can be repeated until a YES status is achieved.

Review the I/M system status indicators. All I/M system status indictors should report YES.

1. Ensure the vehicle is within the Conditions for Running, as specified in the supporting text.
2. Turn OFF all of the accessories, e.g., A/C, blower fan, etc.
3. Set the vehicle parking brake.
4. Verify the transmission is in PARK for automatic transmissions, and NEUTRAL for manual transmissions.
5. Start and allow the engine to idle for 2 minutes.
6. Refer to «Inspection/Maintenance (I/M) System DTC Table»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-troubleshooting-diagnosis) to determine which DTCs are required to run in order to update the misfire monitoring I/M system status to YES.
7. Observe the Not Ran Since Code Cleared display with a scan tool and determine which of the DTCs required for a YES status have not run.
8. Enter the DTC number in the Specific DTC menu of the scan tool.
9. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC.
10. Repeat steps 8 and 9 for any additional required DTCs that have not run. If the I/M System Status did not update to YES, refer to Diagnostic Aids.
11. Observe the emission related DTC portion of the I/M system status display with a scan tool. If the scan tool indicates any DTCs are set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-trouble-code-dtc-list) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The Diesel Fuel Conditioning Module (DFCM) consists of a water separator, an electric prime pump, fuel heater element and a filter element. Fuel is heated by passing through the fuel heater element, which is operated by a built-in thermostatic switch. The thermostatic switch turns the heater element ON and OFF, depending on the fuel temperature. The fuel heater element has voltage anytime the ignition is turned on. The warmed fuel then passes through the fuel filters to the fuel injection pump.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

1. «Inline Harness Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-starting-point-and-in-line-harness-connector-end-views)
2. «Engine Controls Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Check the Water in Fuel lamp for proper operation. Refer to Water-in-Fuel Lamp Always On .

1. Disconnect the fuel heater harness connector from the fuel DFCM housing.
2. Turn ON the ignition with the engine OFF.
3. Probe the fuel heater ignition 1 voltage circuit with a test lamp connected to a good ground. If the test lamp did not illuminate repair the open or short to ground on the ignition 1 voltage circuit.
4. Probe the fuel heater ground circuit at the DFCM housing with a test lamp connected to battery voltage. If the test lamp did not illuminate repair the open in the ground circuit.
5. If all circuits test normal, test the fuel heater thermostatic switch for proper operation. Refer to Component Testing in this diagnostic.

Component Testing

1. Remove the fuel filter from the DFCM housing.
2. Remove the DFCM housing from the vehicle.
3. Connect a DMM between the ignition 1 voltage circuit and the ground circuit of the fuel heater.
4. Cool the thermostatic switch of the fuel heater with ice or refrigeration.
5. Observe the DMM for continuity. If the thermostatic switch does not turn and complete the circuit when the temperature is between -8.4°C to +15.4°C (+16.9°F to +59.8°F) replace the DFCM housing.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Primary Fuel Filter Replacement

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/chevy-express-h1500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The diesel fuel conditioning module (DFCM) consists of a water separator, an electric prime pump, a fuel heater element, and a filter element. Fuel is heated by passing through the fuel heater element, which is operated by a built-in thermostatic switch. The thermostatic switch turns the heater element ON and OFF, depending on the fuel temperature. The fuel heater element has voltage when the ignition is ON. The warmed fuel then passes through the fuel filters to the fuel injection pump.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

1. «Inline Harness Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/body-electrical/#wiring-systems-and-power-management-diagnostic-starting-point-and-in-line-harness-connector-end-views)
2. «Engine Controls Connector End Views»(/chevrolet/chevy-express-h1500/2003-2012/remont/testing-diagnostics/#engine-control-system-fuel-system-66l-lbz-and-lly-introduction-2-of-2)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/chevy-express-h1500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

1. Inspect the water-in-fuel lamp for proper operation. Refer to «Water-in-Fuel Lamp Always On»(/chevrolet/chevy-express-h1500/2003-2012/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges) .
2. Disconnect the fuel heater harness connector from the fuel DFCM housing.
3. Connect a DMM and test for continuity between the terminals of the fuel heater element.
4. Observing the Fuel Temperature parameter with a scan tool. If the fuel temperature is more than 15.5°C (60°F) and continuity is present, the thermostatic switch is stuck ON. Replace the DFCM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Primary Fuel Filter Replacement

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• Scan Tool Data List (Engine Control Module)
• Scan Tool Data List (Glow Plug Control Module)
• Power and Grounding Schematic Icons
• Power and Grounding Connector End Views
• Mass Airflow Sensor/Intake Air Temperature Sensor Replacement
• Testing for Intermittent Conditions and Poor Connections
• Valve Rocker Arm and Shaft Cleaning and Inspection
• Engine Compression Test
• Camshaft and Bearings Cleaning and Inspection
• Oil Consumption Diagnosis
• Temperature Versus Resistance (ECT Sensors)
• Temperature Versus Resistance (Fuel Temperature Sensor)
• Temperature Versus Resistance (IAT Sensor 2)
• Temperature Versus Resistance (IAT Sensor 1)
• Symptoms - Engine Electrical
• Restricted Exhaust
• DTC P0101
• Air Conditioning (A/C) System Performance Test
• Engine Mount Inspection
• Engine Overheating
• Radiator Cleaning
• Loss of Coolant
• Circuit Testing
• Connector Repairs
• Wiring Repairs
• Scan Tool Data Definitions
• Scan Tool Output Controls
• Diagnostic Repair Verification
• Control Module References
• Special Tools
• Battery Inspection/Test (Non-HP2)
• Engine Cranks Slowly
• Symptoms - Engine Exhaust
• Fuel Injector Replacement (Left)
• Fuel Injector Replacement (Right)
• Inline Harness Connector End Views
• Engine Cover Replacement
• Metal Collar Quick Connect Fitting Service
• Fuel Return Pipe Replacement
• Fastener Tightening Specifications
• Diagnostic Trouble Code (DTC) List - Vehicle
• Symptoms - Engine Mechanical
• Engine Flywheel Replacement
• Fuel Tank Draining
• Fuel System Cleaning
• High Idle Switch Programming
• Charge Air Cooler Caution
• Fastener Notice
• Lifting and Jacking the Vehicle
• DTC P0401
• Water-in-Fuel Lamp Always On
• Fuel System Diagnosis
• Contaminants-in-Fuel Diagnosis
• Fuel Pressure Regulator Diagnosis