Engine Control System - 4.6L (LH2) (Troubleshooting): Diagnosis Cadillac STS I

Important Preliminary Inspections Before Starting

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

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»(ref-197634-S11623240522005101200000) .
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. If the intermittent condition exists as a start and then stall, inspect for any DTCs related to the theft deterrent system. Refer to «Diagnostic System Check - Vehicle»(ref-197532-S30271296932005101200000) in Vehicle DTC Information.
7. Verify the proper installation of any of the following non-original equipment accessories: Lights Cellular phone Remote starter system Non-factory installed alarm

1. Use the following tables when diagnosing a symptom concern: «Poor Fuel Fill Quality»(ref-197588-S00464204122005101200000) «Hard Start»(ref-197588-S10149694092005101200000) «Surges/Chuggles»(ref-197588-S06026117892005101200000) «Lack of Power, Sluggishness, or Sponginess»(ref-197588-S22470101362005101200000) «Detonation/Spark Knock»(ref-197588-S30795494842005101200000) «Hesitation, Sag, Stumble»(ref-197588-S04277202942005101200000) «Cuts Out, Misses»(ref-197588-S18547581992005101200000) «Poor Fuel Economy»(ref-197588-S41155127572005101200000) «Rough, Unstable, or Incorrect Idle and Stalling»(ref-197588-S27716170772005101200000) «Dieseling, Run-On»(ref-197588-S02276855072005101200000) «Backfire»(ref-197588-S00639248162005101200000)
2. If the condition can not be isolated using the appropriate table, refer to «Intermittent Conditions»(ref-197588-S12485493972005101200000) for further diagnosis.

Circuit Description

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

Voltage is supplied to the malfunction indicator lamp (MIL) internally by the instrument panel cluster (IPC). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.

The main relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the powertrain relay coil and the armature contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit, via an internal integrated circuit, called an output driver module. When the ECM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allows current to flow from the battery to the following fuses and relays.

1. V8 ECM fuse
2. Post O2
3. ODD coils fuse
4. EVEN coils fuse
5. Pre O2/CAM fuse
6. S/P fan relay
7. Low speed fan relay
8. High speed fan relay

When the ignition switch is turned to the OFF position, power is interrupted to the output driver module in the ECM, and the powertrain relay electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which interrupts current flow to the fuses and relays.

If the powertrain relay fails to close, the engine will crank, but will not run. The GMLAN and class II data communications will be available, with the use of a CANdi module and scan tool.

Diagnostic Aids

1. The main relay will remain powered up for 15 seconds after the ignition switch is turned OFF.
2. The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to «Battery Inspection/Test»(ref-197559-S36532900252005101200000) in Engine Electrical.

Powertrain Relay Diagnosis

When you turn the ignition switch ON, the control module energizes the fuel pump relay which applies power to the in-tank fuel pump. The fuel pump relay will remain ON as long as the engine is running or cranking and the control module is receiving reference pulses. If no reference pulses are present, the control module de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped.

Listen for an audible hiss from the fuel pump when the fuel pump relay is commanded ON. A vibration in the fuel feed line when the fuel pump relay is commanded ON indicates that the fuel pump is operating.

For an intermittent condition, refer to Intermittent Conditions .

The control module enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

1. Excessive resistance in the fuel injector ignition 1 voltage circuit or the fuel injector control circuit may cause the following symptoms: Lean condition Misfire Rough idle
2. Monitoring the misfire current counters, or misfire graph, may help isolate the fuel injector that is causing the condition.
3. Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
4. Perform the fuel injector coil test within the conditions of the customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Fuel Injector Coil Test

1. Operate the vehicle under the condition of the customers concern. Under high temperature conditions, fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J 44175-3 Instruction Manual.
2. If water appears in the fuel sample, perform the following steps: Clean the fuel system. Refer to «Fuel System Cleaning»(ref-197553-S12815630142005101200000) . Replace the fuel filter. Refer to «Fuel Filter Replacement»(ref-197553-S37996048952005101200000) .
3. Subtract 50 from the reading on the DMM in order to obtain the percentage of alcohol in the fuel sample. Refer to the examples in the Fuel Composition Test Examples table.
4. If the fuel sample contains more than 15 percent ethanol, add fresh, regular gasoline to the vehicle's fuel tank.
5. Test the fuel composition.
6. If testing shows the ethanol percentage is still more than 15 percent, replace the fuel in the vehicle. Refer to «Fuel Tank Draining Procedure»(ref-197548-S19614244172005101200000) .

Fuel Composition Test Examples

Alcohol in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If alcohol contamination is suspected, use the following procedure to test the fuel quality

1. Fill the cylinder with fuel to the 90 ml (3.04 oz) mark with a 100 ml (3.38 oz) specified cylinder with 1 ml (0.34 oz) graduation marks.
2. Add 10 ml (0.34 oz) of water in order to bring the total fluid volume to 100 ml (3.38 oz) and install a stopper.
3. Shake the cylinder vigorously for 10-15 seconds.
4. Carefully loosen the stopper in order to release the pressure.
5. Re-install the stopper and shake the cylinder vigorously again for 10-15 seconds.
6. Put the cylinder on a level surface for approximately 5 minutes in order to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer that now contains both alcohol and water will be more than 10 ml (0.37 oz). For example, if the volume of the lower layer is increased to 15 ml (0.51 oz), this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.

Particulate Contaminants in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any contaminants present in the tank will be detected. The sample should be bright and clear. If the sample appears cloudy or contaminated with water as indicated by a water layer at the bottom of the sample, use the following procedure to diagnose the fuel.

1. Draw approximately 0.5 liter (0.53 qt) of fuel with an approved fuel container.
2. Place the cylinder on a level surface for approximately 5 minutes in order to allow settling of the particulate contamination.

Particulate contamination will show up in various shapes and colors. Sand will typically be identified by a white or light brown crystals. Rubber will appear as black and irregular particles. If particles are found, clean the entire fuel system thoroughly. Refer to Fuel System Cleaning .

The ignition system utilizes an individual module/coil for each spark plug. The following 4 circuits support each ignition module/coil assembly.

1. The ignition 1 voltage circuit
2. The ground circuit
3. Ignition control (IC) circuit
4. Low reference circuit

Each ignition module/coil connects directly to its spark plug through a wire spring conductor internal to the spark plug boot. The IC circuits transmits timing pulses from the engine control module (ECM) to each ignition module/coil assembles in the proper sequence for the spark plug firing event. The ECM monitors each IC circuit for improper voltage levels. If an improper voltage level is detected on an IC circuit a DTC will set.

1. This Electronic Ignition (EI) System Diagnostic table assumes that the battery is fully charged. Refer to «Battery Inspection/Test»(ref-197559-S36532900252005101200000) in Engine Electrical.
2. Other electrical, fuel, or mechanical conditions can cause an engine to crank but does not run, or set a DTC P0300 misfire code.
3. An ignition coil, boots, or spark plugs may misfire only when moisture is present. Although difficult to test on this engine, selectively wetting down parts of the ignition system and monitoring for a misfire may help in isolating an intermittent condition. Replace any worn or torn spark plug boots or seals.
4. If the ODD coils or EVEN coils fuse opens, this will also result in the loss of ignition 1 voltage to the odd or even fuel injectors.

Electronic Ignition (EI) System Diagnosis

Conditions for Running

1. The barometric pressure (BARO) is more than 74 kPa.
2. The start-up intake air temperature is between 4-32°C (39-90°F).
3. The difference between the start-up engine coolant temperature (ECT) and the start-up intake air temperature (IAT) is less than 4.5°C (8°F).
4. The battery voltage is more than 10.5 volts.
5. The fuel level is between 15-85 percent.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as heated oxygen sensor (HO2S) heater and evaporative emission (EVAP) system from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures. Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows most of the diagnostics to run and the remaining tests can be performed using the individual System Set Procedures.

The scan tool can be used to monitor each of the I/M System Status indicators during the I/M Complete System Set Procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step even if the remaining portion of the test is not complete. For example, step 3 is designed to run the EVAP, secondary air injection (AIR), and HO2S tests. The procedure instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If all 3 tests have updated to YES within 4 minutes, it is not necessary to continue with the enable conditions and testing can advance to the next step.

Inspection/Maintenance (I/M) System DTC Table

Inspection/Maintenance (I/M) System DTC Table

1. The barometric pressure (BARO) is more than 74 kPa.
2. The engine coolant temperature (ECT) is more than 63°C (145°F).
3. The engine is in closed loop fuel control.

The control module runs a maximum of 12 tests per trip until the Catalyst System Status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

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

1. The barometric pressure (BARO) is more than 74 kPa.
2. The start-up intake air temperature (IAT) is between 4-32°C (39-90°F).
3. The difference between the start-up engine coolant temperature (ECT) and the start-up IAT is less than 4.5°C (8°F).
4. The fuel level is between 15-85 percent.
5. The battery voltage is more than 10.5 volts.
6. The engine is in closed loop fuel control.

If there is an impending failure, the system may require more time to run the diagnostic than allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as cooling fan or an A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure

1. The barometric pressure (BARO) is more than 74 kPa.
2. The engine coolant temperature (ECT) reaches more than 63°C (144°F).
3. The engine is running in closed loop fuel control.

If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor/Oxygen Sensor (HO2S/O2S) System Set Procedure

The battery voltage is more than 10 volts.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor (HO2S) Heater System Set Procedure