Engine Controls - Self Diagnostics - 6.6L: Other Chevrolet Silverado 1500 HD

Code Types

There are 3 types of DTC categories

1. Type "A" Emissions related. Illuminates MIL the first time DTC sets.
2. Type "B" Emissions related. Illuminates MIL if fault is active for 2 consecutive driving cycles.
3. Type "C" Non-emissions related. Does not illuminate MIL, but may illuminate a SERVICE light.

Freeze Frame/Failure Records

ECM stores one freeze frame record (failure record "0") for the first failed test that sets a DTC and illuminates MIL. Freeze frame will not be overwritten unless a misfire or fuel trim DTC is set. Failure records are stored when any DTC is set. Six additional failure records can be stored in ECM. Failure records will be stored for all types of codes, whether or not the MIL is illuminated. If more than 6 DTCs are set, oldest DTC is deleted as newest DTC is stored. Typical failure record data includes

1. Air/fuel ratio.
2. Airflow rate.
3. Fuel trim.
4. Engine speed.
5. Engine load.
6. Engine coolant temperature.
7. Vehicle speed.
8. Throttle position angle.
9. Manifold absolute pressure.
10. Injector base pulse width.
11. Loop status.

Monitors

1. Comprehensive Component Monitor Monitors ECM systems for opens, shorts, grounds and out-of-range sensors. Also monitors rationality of sensors. Rationality is whether the sensors value is consistent with the operating conditions of the other sensors.
2. Misfire Monitor Monitors engine misfire using crankshaft sensor to determine location and severity of misfire. A catalyst damaging misfire will flash the MIL, and a non-catalyst damaging misfire is a normal type "B" code.
3. Fuel Trim Monitor Monitors short and long term fuel trim for being at maximum lean or rich limit.
4. Oxygen Sensor Monitor Monitors all oxygen sensors for maximum voltage level, minimum voltage level and lean rich/rich lean switching rate.
5. Oxygen Sensor Heater Monitor Monitors oxygen sensor heater by watching sensor's time-to-activity after a cold start.
6. Catalyst Monitor Monitors catalyst efficiency by comparing activity rate of precatalyst oxygen sensor and postcatalyst oxygen sensor.
7. EGR Monitor Monitors operation and flow rate of EGR system.
8. EVAP Monitor Monitors EVAP system for large leaks, small leaks and purge flow.
9. Secondary Air Monitor Monitors secondary air operation.

INTERMITTENT CONDITIONS

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated.

Preliminary

Perform the Diagnostic System Check-Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .

Control Module Power & Grounds, & Component Power & Grounds

Poor power or ground connections can cause widely varying symptoms.

1. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test lamp or a Digital Multimeter (DMM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See POWER DISTRIBUTION in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
2. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See GROUND DISTRIBUTION in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

Temperature Sensitivity

1. An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
2. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
3. If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
4. If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
5. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

Incorrect ECM Programming

1. There are only a few situations when reprogramming a ECM is appropriate, such as the following: A new service ECM is installed. A ECM from another vehicle is installed. Revised software or calibration files have been released for this vehicle.
2. Verify that the ECM contains the correct software or calibration. If incorrect programming is found, reprogram the ECM with the most current software or calibration. See «ENGINE CONTROL MODULE»(ref-158516-S10218600282003100300000) under PROGRAMMING.

Duplicating Failure Conditions

1. If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
2. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear the DTCs using the scan tool. Turn the key to OFF and wait 15 seconds. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running DTC. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
3. An alternate method is to drive the vehicle with the Digital Multimeter (DMM) connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs, may help you locate the problem.

Vehicle Data Recorder

The J 42598 Vehicle Data Recorder is connected to the Data Link Connector (DLC) and sent with the customer. The J 42598 captures data for later retrieval and analysis by the technician. Refer to the vehicle data recorder user instructions for more information.

Disconnect Battery

Note. On many OBD-II systems, ECM will retain memory for an extended period of time with battery disconnected. Memory may be retained for several days.

Disconnecting ECM power or battery ground will clear all ECM memory including DTCs, freeze frame, failure records, adaptive learning and system monitors.

Warm-up Cycles

If fault that caused DTC to set is repaired, ECM will begin to count warm-up cycles. After 40 consecutive warm-up cycles with no further faults, ECM will automatically clear DTC from memory.

ENGINE CONTROL MODULE

Note. Service of the ECM should normally consist of either replacement of the ECM or EEPROM programming. If the diagnostic procedures call for the ECM to be replaced, the ECM should be checked first to see if it is the correct part. If it is, remove the faulty ECM and install the new service ECM. The service ECM EEPROM will not be programmed. DTC P0601 and P0602 indicates the EEPROM is not programmed or has malfunctioned.

Note. Programing Engine Control Module requires a compatible scan tool and a Techline® terminal. Procedure uses a Tech 2® scan tool.

Remote Programming

Note. DO NOT program a control module unless you are directed by a service procedure or you are directed by a technical service bulletin. Programming a control module at any other time will not permanently correct a customer's concern.

1. Connect the Tech 2® to the vehicle and obtain the module information using the following procedure: Connect the Tech 2® to the vehicle data link connector (DLC), with the engine and the Tech 2® OFF. Turn ON the Tech 2®. Press Enter at the title screen. Turn ON the ignition, with the engine OFF. Select Service Programming System at the Main Menu. NOTE: Select Request Info Again if a vehicle identification number (VIN) was previously stored in the Tech 2®. Select Request Info. Enter the vehicle description by following the on-screen instructions. Turn OFF all accessories and select Continue. NOTE: Select No and write down the VIN if the VIN is incorrect. Verify that the correct VIN is entered on the Tech 2® and select Yes.
2. Turn OFF the Tech 2®.
3. Disconnect the Tech 2® from the vehicle.
4. Turn OFF the ignition.
5. Transfer the data from the terminal to the Tech 2® using the following procedure: Connect the Tech 2® to the terminal. NOTE: The TIS supports service programming with the Tech 2® scan tool only. Launch the TIS application at the terminal. Select the Service Programming System at the main screen. Highlight the following information on the Select Diagnostic Tool and Programming Process Screen: Select Diagnostic Tool--Select Tech 2® Select Programming Process--Identify whether an existing module is being reprogrammed or a module is being replaced with a new one. Select ECU Location--Select vehicle. Select Next. Verify the connections and select Next. NOTE: You may receive a message stating that the control module could be a service control module if you selected NO to the VIN being correct. Click OK. Verify the VIN and select Next. Select the appropriate controller for the vehicle being serviced. NOTE: When selecting the Vehicle Configuration Index (VCI) programming type, a valid VCI number for the vehicle must be entered. This number may be obtained from the Techline Customer Support. Select the type of programming to be performed from the following categories: Normal--Used for updating an existing calibration or programming a new controller. Vehicle Configuration Index (VCI)--Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure--Used to reconfigure a vehicle for changes in tire size and axle ratios. Select Next NOTE: Refer to Service bulletins before service programming is performed if the bulletins are listed along with the calibration files. Select the appropriate calibration file for the vehicle being serviced. Select Next. NOTE: Select Cancel if you receive a message stating that the calibration selected is already the current calibration in the control module and reprogramming with the same download is not allowed. Verify your selection on the Summary screen. Select Next.
6. Perform the Crankshaft Position Variation Relearn Procedure using the Special Functions feature, if applicable.
7. Close the application and return to the TIS application Selection screen after the download is complete.
8. Turn OFF the Tech 2®.
9. Disconnect the Tech 2® from the terminal.
10. Transfer the data from the Tech 2® to the control module using the following procedure: Connect the Tech 2® to the vehicle DLC, with the engine and the Tech 2® OFF. Turn ON the Tech 2®. Press Enter at the Title screen. Turn ON the ignition, with the engine OFF. Select Service Programming System. Select the Program ECU function on the Tech 2®. Verify the VIN and calibration numbers, select Continue. Follow the on-screen instructions and select Continue. Select continue and exit the program after the Tech 2® displays Programming was Successful.
11. Turn OFF the ignition.
12. Turn OFF the Tech 2®.
13. Disconnect the Tech 2® from the vehicle.
14. Verify programming.

Off-Board Remote Programming

Note. Ensure the Tech 2® and the terminal are both equipped with the latest software before performing SPS.

1. Obtain the vehicle identification number (VIN) of the vehicle for which the module is being programmed.
2. Launch the TIS application at the terminal.
3. Select the Service Programming System.
4. Highlight the following information on the Select Diagnostic Tool and Programming Process screen: Select Diagnostic Tool-Select Tech 2® Select Programming Process-Identify whether an existing module is being reprogrammed or replaced with a new one. Select ECU location-select Off-Board Programming Adapter.
5. Select Next.
6. Follow the directions on the Preparing for Communication screen for connecting the following components: The control module. The Off-Board Programming Adapter (OBPA)--Refer to the TIS Users Guide for a listing of the OBPA. The Tech 2®.
7. Select the Service Programming Request Information function on the Tech 2®.
8. Follow the Tech 2® instructions to obtain the module data and security information.
9. After the Tech 2® has received the data from the module, exit the Request Info mode.
10. Disconnect the Tech 2® from the OBPA.
11. Turn OFF the Tech 2®.
12. Connect the Tech 2® to the terminal.
13. Turn ON the Tech 2®.
14. Select Next at the terminal after the Tech 2® start-up screen appears.
15. Enter the VIN of the vehicle that will be receiving the control module.
16. Select Next.
17. Select the type of programming to be performed from the following categories: Normal--Used for updating an existing calibration or programming a new controller. Vehicle configuration index (VCI)--Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure--Used to reconfigure a vehicle for changes in tire size and axle ratios.
18. Select Next.
19. Select a calibration on the Calibration Selection screen, if necessary.
20. Ensure all the desired folder tabs have a green check mark.
21. Select Next.
22. Verify the current and the selected calibration of the control module on the Summary screen.
23. Select Next.
24. Select OK.
25. On model year 1996 and newer controllers, a crankshaft position (CKP) relearn procedure box may appear. Select OK.
26. Follow the on-screen instructions, if any, when the Program Controller/Programming Complete screen appears.
27. Select Close.
28. Turn OFF the Tech 2®.
29. Disconnect the Tech 2® from the terminal.
30. Connect the Tech 2® to the OBPA.
31. Connect the Tech 2® to the OBPA.
32. Turn ON the Tech 2®.
33. Select Enter at the title screen.
34. Select the Service Programming System at the Main Menu.
35. Select the Program ECU function.
36. Select the Program ECU function.
37. Select Continue.
38. Follow the on-screen instructions.
39. Select Continue.
40. Select Exit when the programming is complete.
41. Turn OFF the OBPA.
42. Turn OFF the Tech 2®.
43. Disconnect the OBPA from the Tech 2® and the control module.

Off-Board Pass-Thru Programming

Note. Ensure the Tech 2® and the terminal are both equipped with the latest software before performing SPS.

1. Launch the TIS application in the terminal.
2. Select the Service Programming System.
3. Highlight the following information on the Select Diagnostic Tool and Programming Process Screen: Select Diagnostic Tool--Select Pass-Thru. Select Programming Process--Identify whether an existing module is being reprogrammed, or a module is being replaced with a new one. Select ECU location--Select Off-Board Programming Adapter.
4. Select Next.
5. Complete all terminal-directed data at the Preparing for Communication/Determine Vehicle screen until Next is highlighted.
6. Complete all terminal-directed data at the Preparing for Communication/Determine Vehicle screen until Next is highlighted.
7. Select Next.
8. Follow the on-screen instructions for connecting the following components: The control module. The Off-Board Programming Adapter (OBPA)--Refer to the TIS Users Guide for a listing of OBPA. The Tech 2®.
9. Select Next.
10. Pass-Thru displays the VIN stored in the control module. If a new control module is being programmed, enter the correct VIN of the vehicle.
11. Select Next.
12. Select the appropriate options if the Options screen appears.
13. Select Next.
14. Select the type of programming to be performed from the following categories: Normal--Used for updating an existing calibration or programming a new controller. Vehicle configuration index (VCI)--Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure--Used to reconfigure a vehicle for changes in tire size and axle ratios.
15. Select Next.
16. Select a calibration selection on the Calibration Selection screen, if necessary.
17. Ensure all the desired calibration folder tabs have a green check mark.
18. Select Next.
19. Verify the current and selected calibration of the control module on the Summary screen.
20. Select Next.
21. Select OK.
22. Select OK.
23. When programming is complete, a Program Controller/Programming Complete screen appears. Follow the on-screen instructions, if any.
24. Select Close.
25. Turn OFF the OBPA.
26. Turn OFF the scan tool.
27. Disconnect the OBPA from the Tech 2® and the control module.

Pass-Thru Programming

Note. The TIS supports service programming with the Tech 2® scan tool only.

1. Launch the TIS application at the terminal. Select the Service Programming System. Highlight the following information on the Select Diagnostic Tool Programming Process screen: Select Diagnostic Tool--Select Pass-Thru Select Programming Process--Identify whether an existing module is being reprogrammed or a module is being replaced with a new one. Select ECU Location--Select vehicle.
2. Select Next.
3. Complete all terminal-directed data on the Preparing for Communication/Determine Vehicle screen until Next is highlighted.
4. Select Next.
5. Follow the instructions on the Preparing for Communication screen.
6. Select Next.
7. Verify the VIN on the Validate Vehicle Identification Number screen.
8. Select Next.
9. If an option screen appears, verify the vehicle configuration and/or RPO information.
10. Select Next.
11. Highlight the appropriate control module and programming type on the Supported Controllers screen.
12. Select Next.
13. Select the proper calibrations on the Calibration Selection screen.
14. Ensure all the folder tabs have a green check mark.
15. Select Next.
16. Verify the current calibrations with the selected calibrations.
17. Select Next.
18. The Transfer Data screen will appear until the progress bar reaches 100 percent. This may take up to 30 minutes.
19. Complete all of the terminal-directed data on the Programming Complete screen.
20. Turn OFF the Tech 2® Disconnect the Tech 2® from the vehicle.
21. Turn OFF the Tech 2®. Disconnect the Tech 2® from the vehicle.

THEFT DETERRENT PASSWORD LEARN PROCEDURE

Note. The Body Control Module (BCM) must be programmed with the proper RPO configurations before performing learn procedures. See PROGRAMMING in appropriate BODY CONTROL MODULES article. If replacing the BCM with a GM Service Parts Operations (SPO) replacement part, the module will learn Passlock® sensor data code immediately. The existing ECM however, must learn the new fuel continue password when the BCM is replaced. If replacing a ECM with a GM Service Parts Operations (SPO) replacement part, after programming, these modules will learn the incoming fuel continue password immediately upon receipt of a password message. Once a password message is received, and a password is learned, a learn procedure must be performed to change this password again. A ECM which has been previously installed in another vehicle will have learned the other vehicle's fuel continue password and will require a learn procedure after programming to learn the current vehicle's password.

Use this procedure after replacing

1. Passlock® Sensor
2. BCM
3. ECM

10-Minute Learn Procedure

Note. This procedure requires a Tech 2® scan tool and a Techline® terminal with current SPS (Service Programming System) software.

1. Connect the Tech 2® to the vehicle.
2. Select "REQUEST INFORMATION" under "SERVICE PROGRAMMING".
3. Disconnect the Tech 2® from the vehicle and connect it to a Techline® terminal.
4. On the Techline® terminal, select "THEFT MODULE RE-LEARN" under "SERVICE PROGRAMMING".
5. Disconnect the Tech 2® from the Techline® terminal and connect it to the vehicle.
6. Turn ON the ignition, with the engine OFF.
7. Select "PROGRAM ECU" under "SERVICE PROGRAMMING".
8. Attempt to start the engine, then release the key to ON (vehicle will not start).
9. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF (the vehicle is now ready to relearn the Passlock® Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK).
10. Turn OFF the ignition, and wait 5 seconds.
11. Start the engine (the vehicle has now learned the password).
12. With the Tech 2® (scan tool), clear any DTCs.

30-Minute Learn Procedure

1. Turn ON the ignition, with the engine OFF.
2. Attempt to start the engine, then release the key to ON (vehicle will not start).
3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
4. Turn OFF the ignition, and wait 5 seconds.
5. Repeat steps 1 - 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock® Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).
6. Start the engine (the vehicle has now learned the Passlock® Sensor Data Code and/or password).
7. With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).

DRIVE CYCLES

See INSPECTION/MAINTENANCE SYSTEM CHECK .

Conditions for Updating I/M System Status

Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a Diagnostic Trouble Code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or any one of the DTCs comprising the monitor have illuminated the Malfunction Indicator Lamp (MIL). Once all of the tests are complete, the I/M System Status display will indicate YES in the Completed column. For example, when the Heated Oxygen Sensor (HO2S) Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
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. Exhaust gas recirculation (EGR) system.
3. Misfire monitoring.

For the specific DTCs required for each system, see

INSPECTION/MAINTENANCE SYSTEM DTCS

table.

INSPECTION/MAINTENANCE SYSTEM DTCS

Procedure

1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158516-S41425574832003100300000) under SELF-DIAGNOSTIC SYSTEM. Repair any DTCs or driveability concerns that would prevent the I/M System Status tests from completing. Did you find and repair a DTC or driveability concern? If yes, go to step 3 . If no, go to next step.
2. Review any service bulletins for software updates that may prevent I/M readiness. Perform any reprogramming or repairs indicated by the service bulletins. Was a reprogramming or repair service required? If yes, see «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(ref-158516-S09216065312003100300000) . If no, go to next step.
3. With a scan tool, observe the I/M System Status display. Is more than one test indicating a NO status? If yes, see «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(ref-158516-S09216065312003100300000) . If no, go to the I/M System Set Procedure for the indicated system.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-158516-S13422433262003100300000) .
2. Preprogram the scan tool with the vehicle information before the ignition is turned ON. Ensure that the vehicle is within the Conditions for Running specified in the supporting text. Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Set the vehicle parking brake. Verify that the transmission is in Park for automatic transmissions and Neutral for manual transmissions. Start the engine and allow the engine to idle. Allow the engine to idle for 2 minutes. When complete, go to next step.
3. In order for the next group of tests to run, the vehicle must operate in the following conditions: Acceleration at part throttle to 50 MPH with this speed maintained until the engine reaches operating temperature. This may be up to 8-10 minutes depending on the start up coolant temperature. Continued operation under these conditions for an additional 3 minutes. After procedure, go to next step.
4. In order for the next group of tests to run, the vehicle must operate in the following conditions: Acceleration at 75 percent throttle until a speed of 68 MPH (110 km/h) is attained. Deceleration to zero MPH (0 km/h). Engine idling for 2 minutes while the following criteria is maintained: Service brake depressed. Automatic transmission in Drive. Manual transmission in Neutral with the clutch pedal depressed. When complete, go to next step.
5. Observe the I/M System Status with a scan tool. Did all of the I/M System Status indicators update to YES? If YES, go to next step. If no, go to the I/M System Set Procedure for the indicated systems.
6. With a scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does the scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158516-S25875883752003100300000) . If no, system is okay.

SUMMARY

If no Diagnostic Trouble Codes (DTCs) are present and a no-start condition exists, proceed to NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 6.6L SIERRA & SILVERADO - DIESEL article. If no DTCs are present and a driveability condition exists, diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.). See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 6.6L SIERRA & SILVERADO - DIESEL article.

MIL Function

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

MIL Illumination

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

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

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

SIERRA 2500HD

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

SIERRA 3500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

SILVERADO 2500HD

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

SILVERADO 3500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.