Engine Controls - 6.6L - Troubleshooting & Diagnosis: Diagnosis GMC Sierra 1500

Important Preliminary Inspections Before Starting

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

1. The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
2. Diagnostic trouble codes (DTCs) are not stored.
3. The scan tool data is within the normal operating range. Refer to «Scan Tool Data List (Engine Control Module)»(ref-238297-S10359974192006072400000) or «Scan Tool Data List (Glow Plug Control Module)»(ref-238297-S11797710032006072400000) .
4. Verify the customer concern and locate the correct symptom. Inspect the items indicated under that symptom.
5. Several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely important, and can lead to correcting a condition without further inspections and can save valuable time.
6. Verify the proper installation of any of the following non-original equipment accessories: Lights Cellular phone Remote starter system Non-factory installed alarm

Visual and Physical Inspection

Inspect the following items

1. The control module grounds for being clean, tight, and in their proper location.
2. The vacuum hoses for splits, kinks, and proper connections, as shown on the Vehicle Emission Control Information label.
3. The wiring for the following items: Proper connections Pinches Cuts
4. Inspect for the installation of any Power Enhancing Devices. It may be necessary to remove these items for proper diagnosis.
5. The following symptom tables contain groups of possible causes for each symptom. The order of these procedures is not important. If the scan tool readings do not indicate the problems, then proceed in a logical order, easiest to inspect or most likely to cause first. In order to determine if a specific vehicle is using a particular system or component, refer to «Engine Controls Schematics»(ref-238192-S32866946162006072400000) for an application.

Diagnostic Fault Information

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Testing

1. With the ignition OFF, disconnect the ECM, turn ON the ignition with the engine OFF. If the MIL remains illuminated, test the MIL control circuit for a short to ground. If the MIL control circuit tested OK and the MIL remained illuminated, replace the instrument panel cluster (IPC). If the MIL control circuit tested OK and the MIL turned OFF when the ECM was disconnected, replace the ECM.
2. With the ignition ON, measure the MIL control circuit for 12 volts at the ECM harness connector to a ground. If there is less than 12 volts, test the MIL ignition voltage and MIL control circuits for the following: An open A short to ground An open fuse
3. Remove the fuse that supplies power to the MIL with a DMM, measure for less than 1 volt from the MIL control circuit in the ECM harness connector to a good ground. If there is more than 1 volt, test the MIL control circuit for a short to voltage or a faulty IPC.
4. Install MIL fuse, the MIL should illuminate when a 3-amp fused jumper wire is connected between the MIL control circuit and a good ground. If the MIL does not illuminate, test the MIL control and MIL voltage circuits for less than 10 ohms of resistance. If the resistance is over 10 ohms, repair the high resistance in the circuit that measured over 10 ohms. If the MIL control and voltage circuit tests OK, replace the IPC. If the MIL illuminates, but does not illuminate when commanded ON with a scan tool, replace the ECM.

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»(ref-238231-S04268144272006072400000) . 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.

1. Inspect for the following conditions: Fuel smell or leak-Refer to «Fuel Leaks»(ref-238231-S22702585102006072400000) . A plugged air filter collapsed air intake duct-Refer to «Air Cleaner Element Replacement»(ref-238192-S34645687802006072400000) . A restricted exhaust system-Refer to «Symptoms - Engine Exhaust»(ref-238286-S14081409412006072400000) . Contaminants in fuel-Refer to «Contaminants-in-Fuel Diagnosis»(ref-238231-S39787907302006072400000) .
2. Observe that the Ignition 1 signal parameter is B+. If the ignition 1 signal is not B+ test the ignition 1 voltage circuit of the ECM for a short to ground, high resistance an open, or a faulty ECM.
3. With the ignition ON and the engine OFF observe that the Actual Fuel Rail Pressure parameter is 1.2-1.9 MPa. If the Actual Fuel Rail Pressure parameter is not 1.2-1.9 MPa, refer to «DTC P0191 - P0193»(ref-238266-S18804841622006072400000) .
4. Crank the engine for 15 seconds. If the Actual Fuel Rail Pressure parameter is less than 10 MPa while cranking the engine, refer to «Fuel System Diagnosis»(ref-238231-S37426576602006072400000) .
5. Perform the Engine Compression Test. Refer to «Engine Compression Test»(ref-238285-S29245004382006072400000) . IMPORTANT: During the replacement of the injectors, inspect the inlet and outlet fittings for corrosion or contamination. Refer to «Contaminants-in-Fuel Diagnosis»(ref-238231-S39787907302006072400000) . If any fuel vapor was emitted during the engine compression test, replace the affected fuel injector. Refer to «Fuel Injector Replacement (Left)»(ref-238192-S20160282322006072400000) or «Fuel Injector Replacement (Right)»(ref-238192-S09868187502006072400000) . If no fuel vapor was emitted during the compression test and the compression tested normal refer to «Fuel System Diagnosis - High Pressure Side»(ref-238231-S18675343932006072400000)

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»(ref-238192-S31949039162006072400000) .

Scheme 591

Callouts For (Scheme 591)

Scheme 592

Callouts For (Scheme 592)

Scheme 593

Callouts For (Scheme 593)

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
4. Fuel filter vent screw not tighten or cross threaded
5. Fuel filter not tighten properly

1. Install the J 44638 to the fuel system service port on the right front side of the engine. See «Special Tools»(ref-238192-S04527813552006072400000) .
2. Prime the fuel system until 10 psi is indicated on the J 44638 . See «Special Tools»(ref-238192-S04527813552006072400000) .
3. Visually inspect the following items for restrictions or leaks: Hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel Fuel leaks between the fuel filter/heater element housing and the fuel injection pump
4. Repair any leaks or replace any components found to be damaged or leaking.
5. Disconnect the fuel supply line at the engine and cap off the pipe on the engine with a rubber plug and clamp. Refer to «Quick Connect Fitting(s) Service (Metal Collar)»(ref-238192-S41378990882006072400000) .
6. Remove the ignition 1 relay and crank the engine 2-3 times in 15-second intervals while observing the J 44638 . See «Special Tools»(ref-238192-S04527813552006072400000) . If more than 5 inches Hg of vacuum was not observed on the vacuum gage during cranking, replace the fuel injection pump. Refer to «Fuel Injection Pump Replacement»(ref-238192-S12947664392006072400000) .
7. Disconnect the fuel return pipe and install a J 23738-A .
8. Apply 25 inches Hg of vacuum to the fuel return pipe and wait for at least one minute for the system to stabilize. Repeat this step 6 additional times. If vacuum drops below 8 inches Hg of vacuum within 10 minutes, repair the air leak at fuel filter/heater element housing connections or at the fuel hoses/pipes, on the engine.
9. Disconnect and plug the chassis fuel supply line at the fuel tank. Refer to «Quick Connect Fitting(s) Service (Metal Collar)»(ref-238192-S41378990882006072400000) .
10. Apply at least 25 inches Hg of vacuum to the supply hose with the J 23738-A and wait more than one minute for the system to stabilize. Repeat this action 10 times. If the vacuum drops below 8 inches Hg of vacuum within 10 minutes, repair the air leak in the fuel supply line between the engine and fuel tank.
11. Except for the fuel supply line, install all components and lines that were previously removed or disconnected.
12. Install the EN-47969 on the fuel supply line at the engine. See «Special Tools»(ref-238192-S04527813552006072400000) . Create a vertical loop in the hose to observe the incoming fuel for air bubbles.
13. Prime the fuel system 30 times to remove the air from the fuel hoses. Continue to prime the fuel system until the engine starts and runs.
14. Run the engine for at least 10 minutes to allow the fuel system to stabilize, and purge any air from the system.
15. Observe the fuel entering the EN-47969 for air bubbles. See «Special Tools»(ref-238192-S04527813552006072400000) . If air bubbles were observed entering the transparent hose, test the fuel sender for leaks. Refer to «Fuel Sender Assembly Replacement»(ref-238192-S35996463152006072400000) .
16. 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»(ref-238192-S04527813552006072400000) . Prime the fuel system 30 times to remove the air from the fuel hoses. Continue to prime the fuel system until the engine starts and runs. Observe the fuel entering the transparent hose. If air bubbles are still present, refer to «Diagnostic Aids»(ref-238231-S18856179352006072400000) . If no air bubbles are present, remove the EN-47969 and run the engine to ensure no fuel leaks exist. See «Special Tools»(ref-238192-S04527813552006072400000) .

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

1. Disconnect the fuel return line at the engine. Refer to «Quick Connect Fitting(s) Service (Metal Collar)»(ref-238192-S41378990882006072400000) .
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.

1. If no air flow was present, inspect for a restricted or a damaged fuel return line. Repair or replace the fuel return line.

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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.

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. 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»(ref-238192-S21031218502006072400000) . 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»(ref-238192-S21031218502006072400000) .
3. Remove the fuel return hose from the fuel injectors of the right cylinder bank. Refer to «Fuel Injector Return Pipe Replacement - Right»(ref-238192-S09151704722006072400000) .
4. Connect the yellow hoses from the J 45873 to the Fuel Injector Test Adapters. See «Special Tools»(ref-238192-S04527813552006072400000) .
5. Connect the Fuel Injector Test Adapters with yellow hoses to each fuel injector return port of the right cylinder bank, and install the retaining clips.
6. Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical order. See «Special Tools»(ref-238192-S04527813552006072400000) .
7. Connect the fuel return hoses to the J 45873-31 to prevent leakage. 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»(ref-238192-S04527813552006072400000) . 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»(ref-238192-S35286702122006072400000) for the desired quantities. If high return flow was recorded, remove the fuel feed pipes from any fuel injectors that have high return flow and install the EN 47589 to the fuel rail outlets. See «Special Tools»(ref-238192-S04527813552006072400000) .
11. Retest the fuel return flow, using the «Fuel System Specifications»(ref-238192-S35286702122006072400000) , and cap any additional high return flow injectors.
12. 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. Replace the fuel injectors that had capped off lines. Refer to «Fuel Injector Replacement (Left)»(ref-238192-S20160282322006072400000) or «Fuel Injector Replacement (Right)»(ref-238192-S09868187502006072400000) .
13. Start and idle the engine. You may have to prime the fuel system before the engine will start.
14. Command the fuel pressure control to 180 MPa with a scan tool. If the fuel pressure in less than 145 MPa replace the fuel injection pump. Refer to «Fuel Injection Pump Replacement»(ref-238192-S12947664392006072400000) .
15. 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.
16. Operate the vehicle in order to verify the repairs.

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.

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»(ref-238231-S35768631632006072400000) . If the fuel pressure regulator graph was not normal, replace the fuel pressure regulator «Fuel Pressure Regulator Replacement»(ref-238192-S31949039162006072400000) .
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 (Automatic Transmission)»(ref-238224-S02655580572006072400000) or «Engine Flywheel Replacement (Manual Transmission)»(ref-238224-S26900248102006072400000) . 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 indicate a cylinder with a different power contribution, refer to «Diagnostic Aids»(ref-238231-S01721443432006072400000) .
9. Perform the engine compression test. Refer to «Engine Compression Test»(ref-238285-S29245004382006072400000) . If the compression test indicated any of the cylinder had low compression, refer to «Symptoms - Engine Mechanical»(ref-238285-S03174357612006072400000) .
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)»(ref-238192-S20160282322006072400000) or «Fuel Injector Replacement (Right)»(ref-238192-S09868187502006072400000) .
11. Operate the vehicle under the conditions in which the concern occurred.

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 engine coolant temperature (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»(ref-238231-S35768631632006072400000) . If the fuel pressure regulator graph was not normal, replace the fuel pressure regulator. Refer to «Fuel Pressure Regulator Replacement»(ref-238192-S31949039162006072400000) .
4. Apply the parking brake and place the transmission in Drive.
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. Observe the Balancing Rate parameters with a scan tool and record the values for Cylinders 1-8.
8. Repeat steps 4-7 with the transmission in Neutral. Balance Rates should be between +4 mm 3 and -4 mm 3 in Neutral or Park and between +6 mm 3 and -6 mm 3 in Drive. Perform the Cylinder Power Balance Test in Special Functions if not within the specifications.
9. 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»(ref-238231-S26970393752006072400000) .
10. Perform the engine compression test. Refer to «Engine Compression Test»(ref-238285-S29245004382006072400000) . If the compression test indicated any of the cylinder had low compression, refer to «Symptoms - Engine Mechanical»(ref-238285-S03174357612006072400000) .
11. 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)»(ref-238192-S20160282322006072400000) or «Fuel Injector Replacement (Right)»(ref-238192-S09868187502006072400000) .
12. Operate the vehicle under the conditions in which the concern occurred.

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.

Contaminants-in-Fuel Diagnosis

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

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

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

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

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

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

Remove and inspect the fuel filter.

1. If water, gasoline or fungi/bacteria are not present, end the inspection.
2. If water or fungi/bacteria are present, go to Cleaning Water from the Fuel System. Refer to «Fuel System Cleaning»(ref-238192-S22532537292006072400000) .
3. If gasoline is present, go to Cleaning Gasoline from the Fuel System. Refer to «Fuel System Cleaning»(ref-238192-S22532537292006072400000) .

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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»(ref-238231-S28427568612006072400000) .

Inspection/Maintenance (I/M) System DTC Table

Inspection/Maintenance (I/M) System DTC Table

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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.

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»(ref-238231-S07294803142006072400000) 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»(ref-238231-S25161757752006072400000) .
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»(ref-238177-S17723883262006072400000) .

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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 top of the fuel filter/heater element 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 short to ground or open in the ignition 1 voltage circuit.
4. Probe the fuel heater ground circuit at the fuel filter/heater element housing with a test lamp connected to battery voltage. If the test lamp did not illuminate repair the open in the ground circuit between the fuel filter/heater element housing and the engine ground.
5. Remove the fuel filter from the fuel filter/heater element housing. Test the ignition 1 voltage circuit and the ground circuit for an open in the fuel filter/heater element housing. If either circuit tested open replace the fuel filter/heater element housing.
6. If all circuits test normal, test the fuel heater thermostatic switch for proper operation. Refer to «Component Testing»(ref-238231-S20363038002006072400000) .

Component Testing

1. Remove the fuel filter/heater element housing from the vehicle.
2. Connect the ignition 1 voltage circuit of the fuel heater to a battery voltage source and connect the ground circuit of the fuel heater to a ground.
3. Cool the thermostatic switch of the fuel heater with ice.
4. Observe the heating element. If the thermostatic switch does not turn on the heater element when the temperature is between -8.4°C and +15.4°C (+16.9°F and +59.8°F) replace the fuel filter/heater element housing.

Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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

1. Turn ON the ignition, with the engine OFF.
2. Disconnect the fuel heater connector.
3. With the fuel temperature above 21°C (70°F), test for continuity between the ignition 1 voltage terminal and the fuel filter/heater element housing. If continuity was present, the thermostatic switch is stuck ON. Replace the fuel filter/heater element housing.