Engine Controls and Fuel - 6.6l (Lgh) - Description and Operation Chevrolet Express G1500

Diesel Exhaust Fluid (DEF) Warning Strategy (DEF Level)

An adequate on-board supply of Diesel Exhaust Fluid (DEF) is critical for the reduction of exhaust Oxides of Nitrogen (NOx) levels within the Selective Catalyst Reduction (SCR) stage. This vehicle provides the driver with an elaborate series of prompts and warnings that are initiated when the DEF level falls below a calibrated value.

The Engine Control Module (ECM) monitors the DEF level and consumption rate in order to calculate an estimated range in miles remaining until the DEF reservoir is empty. DEF levels are detected by the 3-position solid-state DEF level sensor. Typically, DEF warnings begin once the estimated mileage falls below 1,609 km (1,000 mi). Once initiated, DEF warnings grow increasingly more serious as the remaining mileage decreases without a DEF refill. The vehicle's current DEF warning level is displayed on the scan tool as Reductant Level Warning Indicator Command Level 1 through Level 14.

Warning Level 1

Warning Level 1 is triggered when the DEF level falls below the top-most position of the DEF Level Sensor and the estimated range remaining is greater than 1609 km (1000 mi). No prompts or warnings are presented to the driver.

Warning Level 2

Warning Level 2 is triggered when the estimated range remaining falls below 1,609 km (1,000 mi) based on current DEF consumption rates. The Driver Information Center (DIC) displays the message Exhaust Fluid Range X MI, where X is the estimated range remaining in miles. This message remains on the DIC until acknowledged by the driver.

Warning Level 3

Warning Level 2 automatically advances to Warning Level 3 when the ECM detects an ignition ON to ignition OFF event. A level 3 warning remains active as long as the estimated range remaining is greater than 483 km (300 mi) based on current DEF consumption rates.

Warning Level 4

Warning Level 4 is triggered when the estimated range remaining falls below 483 km (300 mi) based on current DEF consumption rates. The message Exhaust Fluid Range X MI, where X is the estimated range remaining in miles is displayed in the DIC. This message is also displayed at the beginning of each ignition cycle. This message remains on the DIC until acknowledged by the driver.

Warning Level 5

Warning Level 5 is triggered when the estimated range remaining is less than approximately 121 km (75 mi) based on current DEF consumption rates. The message Exhaust Fluid Low - Speed Limited Soon, is displayed on the DIC. This message is also displayed at the beginning of each ignition cycle. This message remains in the DIC until acknowledged by the driver.

Warning Level 6

Warning Level 6 is triggered when the estimated range remaining is less than approximately 0 km (0 mi) based on current DEF consumption rates. The driver will hear 4 chimes on entering Warning Level 6. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. 644 km (400 miles) until 105 km/h (65 mph) Max Speed

The messages are also displayed at the beginning of each ignition cycle. The Exhaust Fluid Empty Refill Now message remains on the DIC until acknowledged by the driver. The 644 km/h (400 mph) until 105 km/h (65 mph) Max Speed mileage countdown until speed limitation will remain displayed in the DIC.

The DEF Indicator in the instrument panel is continuously illuminated. The vehicle remains in Warning Level 6 until the DEF reservoir is refilled or the first mileage countdown expires.

After the first mileage countdown expires, the system will advance from Warning Level 6 to Warning Level 7.

Warning Level 7

Warning Level 7 is active after the first mileage countdown expires. The driver will hear 4 chimes on entering Warning Level 7. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Transitioning to 105 km/h (65 mph) Max Speed

The messages are alternately displayed every 5 seconds on the DIC. Exhaust Fluid Empty Refill Now remains on the DIC until acknowledged by the driver; however, the Transitioning to 105 km/h (65 mph) Max Speed remains displayed in the DIC.

The DEF Indicator in the instrument panel is continuously illuminated.

Vehicle speed limit is ramping down from Max Speed limit to the limit of 105 km/h (65 mph).

Warning Level 8

Warning Level 8 is triggered after the speed limit ramp-down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 8. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Speed Limited to 105 km/h (65 mph)
3. 120 km (75 miles) until 89 km/h (55 mph) Max Speed

The messages are alternately displayed every 5 seconds on the DIC. The Exhaust Fluid Empty Refill Now message remains in the DIC until acknowledged by the driver and occurs every ignition cycle. The speed limited and mileage countdown for speed limitation remain displayed in the DIC

The DEF Indicator in the instrument panel is continuously illuminated. The vehicle remains in Warning Level 8 until the DEF reservoir is refilled or the second mileage countdown expires.

Vehicle speed is limited to 105 km/h (65 mph).

Warning Level 9

Warning Level 9 is triggered after the second mileage countdown expires without a refill of the DEF reservoir. The driver will hear 4 chimes on entering Warning Level 9. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Transitioning to 89 km/h (55 mph) Max Speed

The messages are alternately displayed every 5 seconds on the DIC. Exhaust Fluid Empty Refill Now remains in the DIC until acknowledged by the driver; however, the Transitioning to 89 km/h (55 mph) Max Speed message remains displayed in the DIC.

The DEF Indicator in the instrument panel flashes continuously.

Vehicle speed limit is ramping down from 105 km/h (65 mph) Max Speed limit to 89 km/h (55 mph).

Warning Level 10

Warning Level 10 is triggered after the speed limit ramp-down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 10. The 4 chimes are repeated 2 more times during this ignition cycle. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Speed Limited to 89 km/h (55 mph)
3. 120 km (75 miles) until 7 km/h (4 mph) Max Speed

The messages are alternately displayed every 5 seconds in the DIC. Exhaust Fluid Empty Refill Now remains in the DIC until acknowledged by the driver; however, the speed limited and mileage countdown for speed limitation remain displayed in the DIC.

The DEF Indicator in the instrument panel flashes continuously. The vehicle remains in Warning Level 10 until the DEF reservoir is refilled or the third mileage countdown expires.

Vehicle speed is limited to 89 km/h (55 mph).

Warning Level 11

Warning Level 11 is not used.

Warning Level 12

Warning Level 12 is not used.

Warning Level 13

Warning Level 13 is triggered after the third mileage countdown expires without a refill of the DEF reservoir. The driver will hear 4 chimes on entering Warning Level 13. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Transitioning to 7 km/h (4 mph) Max Speed

The messages are alternately displayed every 5 seconds in the DIC. Exhaust Fluid Empty Refill Now remains in the DIC until acknowledged by the driver; however, the Transitioning to 7 km/h (4 mph) Max Speed message remains displayed in the DIC.

The DEF Indicator in the instrument panel flashes continuously. Vehicle speed limit is ramping down from 89 km/h (55 mph) max speed limit to 7 km/h (4 mph).

Warning Level 14

Warning Level 14 is triggered after the speed limit ramp-down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 14. The 4 chimes are repeated every 3 minutes. The DIC displays the following messages

1. Exhaust Fluid Empty Refill Now
2. Speed Limited to 7 km/h (4 mph)

The messages are alternately displayed every 5 seconds in the DIC. Exhaust Fluid Empty Refill Now remains in the DIC until acknowledged by the driver; however, the Speed Limited to 7 km/h (4 mph) message remains displayed in the DIC.

The DEF Indicator in the instrument panel flashes continuously. The vehicle remains in Warning Level 14 until the DEF reservoir is refilled.

Vehicle speed is limited to 7 km/h (4 mph).

Diesel Exhaust Fluid (DEF) Warning Strategy (DEF Quality)

A supply of clean, fresh Diesel Exhaust Fluid (DEF) is critical for optimum Selective Catalyst Reduction (SCR) efficiency. SCR efficiency is determined by monitoring the Nitrogen Oxide (NOx) sensors located upstream and downstream of the SCR. This vehicle provides the driver with an elaborate series of prompts and warnings that are initiated when the Engine Control Module (ECM) detects a drop in the SCR NOx reduction efficiency suggesting a diluted or contaminated DEF supply.

When contaminated or diluted DEF is suspected, the ECM initiates the DEF Quality warning process. Once initiated, DEF quality warnings grow increasingly more serious as the vehicle continues to be driven. The vehicle's current DEF quality warning status is displayed on the scan tool. When a drop in SCR efficiency is detected, the normally OFF Reductant Field Quality Warning Indicator Command will display Warning Level 1 through Warning Level 11 depending on the number of miles driven. The series of DEF Quality Warnings alert the driver that DEF system service is urgently needed.

Warning Level 1 is triggered when the ECM first detects the SCR efficiency is below a calibrated value. The Driver Information Center (DIC) displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. 160 km (99 miles) until 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the mileage countdown remains displayed in the DIC. The DEF Indicator in the instrument panel is illuminated.

Warning Level 2 is triggered after the first mileage countdown expires without a DEF fluid service. The driver will hear 4 chimes on entering Warning Level 2. The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Transitioning to 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the Transitioning to 105 km/h (65 mph) Max Speed remains displayed in the DIC. The DEF Indicator in the instrument panel is illuminated. Vehicle speed limit is ramping down from max speed limit to the limit of 105 km/h (65 mph).

Warning Level 2 automatically advances to Warning Level 3 after speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 3. The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Speed Limited to 105 km/h (65 mph)
4. 120 km (75 miles) Until 89 km/h (55 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the speed limitation and mileage countdown remains displayed on the DIC. The DEF Indicator in the instrument panel is illuminated.

Vehicle speed is limited to 105 km/h (65 mph).

Warning Level 4 is triggered after the second mileage countdown expires without a DEF fluid service. The driver will hear 4 chimes on entering Warning Level 4. The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Transitioning to 89 km/h (55 mph)

The messages alternate every 5 seconds until acknowledged by the driver; however, the Transitioning to 89 km/h (55 mph) remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously. Vehicle speed limit is ramping down from 105 km/h (65 mph) max speed limit to 89 km/h (55 mph).

Warning Level 5 is triggered after the speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 5. The series of 4 chimes will repeat 3 additional times every 3 minutes . The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Speed Limited to 89 km/h (55 mph)
4. 120 km (75 miles) Until 7 km/h (4 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the speed limitation and mileage countdown remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously.

Vehicle speed is limited to 89 km/h (55 mph).

Warning Level 6 is not used.

Warning Level 7 is not used.

Warning Level 8 is not used.

Warning Level 9 is not used.

Warning Level 10 is triggered after the third mileage counter expires without a DEF fluid service. The driver will hear 4 chimes on entering Warning Level 10. The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Transitioning to 7 km (4 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the Transitioning to 6 km/h (4 mph) Max Speed remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously. Vehicle speed limit is ramping down from 89 km/h (55 mph) max speed limit to 7 km/h (4 mph).

Warning Level 11 is triggered after the speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes every 3 minutes on entering Warning Level 11. The series of 4 chimes will repeat every 3 minutes. The DIC displays the following messages

1. Exhaust Fluid Quality Poor
2. See Owner's Manual Now
3. Speed Limited to 7 km (4 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the Speed Limited to 7 km (4 mph) Max Speed remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously.

Vehicle speed is limited to 7 km/h (4 mph).

Diesel Exhaust Fluid (DEF) Warning Strategy (Anti-Tampering)

The reductant system supplies the Selective Catalyst Reduction (SCR) stage of the vehicle's exhaust after treatment system with the Diesel Exhaust Fluid (DEF) required to reduce exhaust Oxides of Nitrogen (NOx) levels. The Engine Control Module (ECM) continuously monitors the performance of the reductant system during operation.

When the conditions associated with an attempt to disable reductant system operation are detected, the ECM activates the anti-tampering feature and presents the driver with a series of prompts and warnings.

Once initiated, anti-tampering warnings grow increasingly more serious as the vehicle continues to be driven. The vehicle's current warning status is displayed on the scan tool. When tampering is suspected, the normally OFF Reductant System Malfunction Warning Indicator Command will display Warning Level 1 through Warning Level 11 depending on the number of miles driven. The series anti-tampering warnings alert the driver that reductant system service is urgently needed.

Warning Level 1 is triggered when the ECM first detects an abnormal value on a reductant system circuit. The Driver Information Center (DIC) displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. 160 km (99 miles) until 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds in the DIC until acknowledged by the driver; however, the mileage countdown message remains in the DIC. The DEF Indicator in the instrument panel is illuminated.

Warning Level 2 is triggered after the first mileage counter expires. The driver will hear 4 chimes on entering Warning Level 2. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Transitioning to 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds in the DIC until acknowledged by the driver; however, the Transitioning to 105 km/h (65 mph) Max Speed remains in the DIC. The DEF Indicator in the instrument panel is illuminated. Vehicle speed limit is ramping down from max speed limit to the limit of 105 km/h (65 mph).

Warning Level 2 automatically advances to Warning Level 3 after the speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 3. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Speed Limited to 105 km/h (65 mph)
4. 120 km (75 miles) Until 89 km/h (55 mph) Max Speed

The messages alternate every 5 seconds in the DIC until acknowledged by the driver; however, the Speed Limited to 105 km/h (65 mph) remains in the DIC. The DEF Indicator in the instrument panel is illuminated.

Vehicle speed is limited to 105 km/h (65 mph).

Warning Level 4 is triggered after the second mileage counter expires. The driver will hear 4 chimes on entering Warning Level 4. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Transitioning to 89 km/h (55 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the Transitioning to 89 km/h (55 mph) Max Speed remain displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously. Vehicle speed limit is ramping down from 105 km/h (65 mph) max speed limit to 89 km/h (55 mph).

Warning Level 4 automatically advances to Warning Level 5 after speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 5. The series of 4 chimes will repeat 3 times every 3 minutes during each ignition cycle until the vehicle is serviced. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Speed Limited to 89 km/h (55 mph)
4. 120 km (75 miles) Until 7 km/h (4 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the speed limitation and mileage countdown remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously.

Vehicle speed is limited to 89 km/h (55 mph)

Warning Level 6 is not used

Warning Level 7 is not used

Warning Level 8 is not used

Warning Level 9 is not used

Warning Level 5 automatically advances to Warning Level 10 after third mileage counter expires or a key cycle. The driver will hear 4 chimes on entering Warning Level 10. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Transitioning to 7 km/h (4 mph)

The messages alternate every 5 seconds until acknowledged by the driver; however, the Transitioning to 7 km/h (4 mph) remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously. Vehicle speed limit is ramping down from 89 km/h (55 mph) max speed limit to 7 km/h (4 mph).

Warning Level 10 automatically advances to Warning Level 11 after speed limit ramp down is complete or a key cycle. The driver will hear 4 chimes on entering Warning Level 11. The series of 4 chimes will repeat every 3 minutes until the vehicle is serviced. The DIC displays the following messages

1. Service Exhaust Fluid System
2. See Owner's Manual Now
3. Speed Limited to 7 km/h (4 mph)

The messages alternate every 5 seconds until acknowledged by the driver; however, the Speed Limited to 7 km/h (4 mph) remains displayed in the DIC. The DEF Indicator in the instrument panel flashes continuously.

Vehicle speed is limited to 7 km/h (4 mph).

Diesel Exhaust Fluid (DEF) Warning Strategy (Emission Control)

The reductant system supplies the Selective Catalyst Reduction (SCR) stage of the vehicle's exhaust aftertreatment system with the Diesel Exhaust Fluid (DEF) required to reduce exhaust Oxides of Nitrogen (NOx) levels. The Engine Control Module (ECM) continuously monitors the performance of the emission system during operation

When the conditions associated with a fault in the emission system operation are detected, the ECM activates the emission control feature and presents the driver with a series of prompts and warnings.

Once initiated, emission control warnings grow increasingly more serious as the vehicle continues to be driven. The vehicle's current warning status is not displayed on the scan tool. The series emission control warnings alert the driver that EGR/SCR system service is urgently needed.

Warning Level 1 is triggered when the ECM first detects an EGR or SCR dosing inhibit fault. The Driver Information Center (DIC) displays the following messages

1. Service Emission System
2. See Owner's Manual Now
3. 282 km (175 miles) until 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds and remain in the DIC until acknowledged by the driver, however the mileage countdown remains displayed in the DIC.

Warning Level 2 is triggered after the first mileage countdown expires without vehicle service. The driver will hear 4 chimes on entering Warning Level 2. The DIC displays the following messages

1. Service Emission System
2. See Owner's Manual Now
3. Transitioning to 105 km/h (65 mph) Max Speed

The messages alternate every 5 seconds in the DIC until acknowledged by the driver.

Warning Level 2 automatically advances to Warning Level 3 after speed limit ramp down is complete or a key OFF for at least 2 minutes. The driver will hear 4 chimes on entering Warning Level 3. The DIC displays the following messages

1. Service Emission System
2. See Owner's Manual Now
3. Speed Limited to 105 km/h (65 mph)
4. 120 km (75 miles) Until 89 km/h (55 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver; however, the Speed Limited to 105 km/h (65 mph), remains displayed in the DIC.

Vehicle speed is limited to 105 km/h (65 mph).

Warning Level 4 is not used.

Warning Level 5 is not used.

Warning Level 6 is triggered when the second mileage countdown expires without vehicle service. The driver will hear 4 chimes on entering Warning Level 6. The DIC displays the following messages

1. Service Emission System
2. See Owner's Manual Now
3. Transitioning to 89 km/h (55 mph) Max Speed

The messages alternate every 5 seconds until acknowledged by the driver.

Warning Level 6 automatically advances to Warning Level 7 after speed limit ramp down is complete or a key OFF for at least 2 minutes. The driver will hear 4 chimes upon entering Warning Level 7. The series of 4 chimes will repeat every 3 minutes until the vehicle is serviced. The DIC displays the following messages

1. Service Emission System
2. See Owner's Manual Now
3. Speed Limited to 89 km/h (55 mph)

The messages alternate every 5 seconds until acknowledged by the driver, however, the Speed Limited to 89 km/h (55 mph), remains displayed in the DIC.

Engine Control Module Description

The Engine Control Module (ECM) interacts with many emission related components and systems, and monitors emission related components and systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance degrades. The ECM is part of a network and communicates with various other vehicle control modules.

Malfunction indicator lamp (MIL) operation and DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC is emissions related. Type C is a non-emissions related DTC.

The ECM is the control center of the engine controls system. Review the components and wiring diagrams in order to determine which systems are controlled by the ECM.

The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect engine performance and emissions. The ECM also performs diagnostic tests on various parts of the system and can turn on the MIL when it recognizes an operational problem that affects emissions. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified by the particular DTC that is set. This aids the technician in making repairs.

ECM Function

The ECM can supply 5 V or 12 V to various sensors or switches. This is done through pull-up resistors to regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeter will not give an accurate reading due to low input resistance. Therefore, a digital multimeter (DMM) with at least 10 megaohms input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits by controlling the ground or the power feed circuit through transistors or a device called an output driver module.

EEPROM

The electronically erasable programmable read only memory (EEPROM) is an integral part of the ECM. The EEPROM contains program and calibration information that the ECM needs in order to control engine operation.

Special equipment, as well as the correct program and calibration for the vehicle, are required in order to reprogram the ECM.

Data Link Connector (DLC)

The data link connector (DLC) provides serial data communication for ECM diagnosis. This connector allows the technician to use a scan tool in order to monitor various serial data parameters, and display DTC information. The DLC is located inside the driver's compartment, underneath the instrument panel.

Malfunction Indicator Lamp (MIL)

The malfunction indicator lamp (MIL) is inside the instrument panel cluster (IPC). The MIL is controlled by the ECM and illuminates when the ECM detects a condition that affects vehicle emissions.

ECM Service Precautions

The ECM, by design, can withstand normal current draws that are associated with vehicle operations. However, care must be used in order to avoid overloading any of these circuits. When testing for opens or shorts, do not ground or apply voltage to any of the ECM circuits unless the diagnostic procedure instructs you to do so. These circuits should only be tested with a DMM unless the diagnostic procedure instructs otherwise.

Emissions Diagnosis For State I/M Programs

This OBD II equipped vehicle is designed to diagnose any conditions that could lead to excessive levels of the following emissions

1. Hydrocarbons (HC)
2. Carbon monoxide (CO)
3. Oxides of nitrogen (NOx)
4. Evaporative emission (EVAP) system losses

Should this vehicle's on-board diagnostic system (ECM) detect a condition that could result in excessive emissions, the ECM turns ON the MIL and stores a DTC that is associated with the condition.

Aftermarket (Add-On) Electrical And Vacuum Equipment

Aftermarket, add-on, electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicle's electrical or vacuum systems. No allowances have been made in the vehicle design for this type of equipment.

Add-on electrical equipment, even when installed to these strict guidelines, may still cause the powertrain system to malfunction. This may also include equipment not connected to the vehicle electrical system, such as portable telephones and radios. Therefore, the first step in diagnosing any powertrain condition is to eliminate all of the aftermarket electrical equipment from the vehicle. After this is done, if the problem still exists, the problem may be diagnosed in the normal manner.

Electrostatic Discharge (ESD) Damage

Note. In order to prevent possible electrostatic discharge damage to the ECM, DO NOT touch the connector pins on the ECM.

The electronic components that are used in the control systems are often designed to carry very low voltage. These electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 V of static electricity can cause damage to some electronic components. By comparison, it takes as much as 4,000 V for a person to even feel a static discharge.

There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat.

Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite polarity. Static charges can cause damage, therefore, it is important to use care when handling and testing electronic components.

Emissions Control Information Label

The underhood Vehicle Emissions Control Information Label contains important emission specifications. This identifies the year, the displacement of the engine in liters, and the class of the vehicle.

This label is located in the engine compartment of every General Motors vehicle. If the label has been removed, it can be ordered from GM service parts operations (GMSPO).

Exhaust Gas Recirculation (EGR) System Description

The Exhaust Gas Recirculation (EGR) System is used to reduce the amount of nitrogen oxide (NOx) emission levels caused by high combustion temperatures. At temperatures above 1,371°C (2,500°F), oxygen and nitrogen combine to form NOx. Introducing small amounts of exhaust gas back into the combustion chamber displaces the amount of oxygen entering the engine. With less oxygen in the air/fuel mixture, the combustion pressures are reduced, and as a result, combustion temperatures are decreased, restricting the formation of NOx.

The EGR system on the LGH engine consists of single or dual EGR coolers, an EGR valve and a Mass Air Flow (MAF) sensor.

The EGR system on the LML engine utilizes dual EGR coolers, an EGR valve, MAF sensor and an EGR cooler bypass valve, which is controlled by the ECM, to prevent coking of the EGR coolers during light load and idling.

The EGR and EGR cooler bypass valve motors are Direct Current (DC) motors utilizing a multi-stage gear drive connected to the valve stem. The motors are controlled by the ECM and actively force the valves open and closed. Each valve contains an integral valve position sensor which reflects the true position of the valve. The MAF sensor signal is used by the Engine Control Module (ECM) to detect the proper amount of EGR flow. The ECM continually does a consistency check on the indicated EGR flow by comparing the desired MAF to the actual MAF. If the actual MAF is less than or greater than a calibrated threshold level, the amount of EGR flow is determined to be out of range and a DTC will set.

Scheme 133

The EGR valve is controlled by the ECM through the EGR motor high control and EGR motor low control circuits. The ECM supplies voltage that is near ignition voltage to the high and low control circuits at all times. This voltage is used by the ECM as a reference voltage during non EGR operation in order to detect circuit failures. The ECM Pulse Width Modulates (PWM) the low control circuit to ground when the EGR valve is commanded open. A lower pulse width increases the open position of the valve. In order to close the EGR valve, the ECM will PWM the high control circuit to ground.

When the ignition is turned OFF, the EGR valve executes a series of clean and learn operations. The valve goes through a number of full sweeps, (cleaning operation), followed by a number of learn events that pushes the poppet just off the seat and then pulls it into the seat to determine the correct sensor position voltage. Certain environmental conditions, such as low temperature, may inhibit the clean and learn operations, so they may not occur during every ignition cycle.

The EGR valve has an integral position sensor that feeds back to the ECM. The sensor is located on the output gear of the actuator and is a non-contacting type sensor. The ECM uses the position sensor to determine the position of the valve. The ECM sends a reference voltage through the 5-volt reference circuit to the EGR position sensor. The ECM provides a voltage return path for the sensor through the low reference circuit. A variable voltage signal, based on the EGR valve position, is sent from the sensor to the ECM through the EGR position sensor signal circuit.

The ECM commands the required valve position based on engine requirements. The outlet of the EGR valve flows directly into the intake manifold.

Scheme 134

The EGR Cooler Bypass Valve (if equipped) is fed off of the passenger side rear exhaust bank. The ECM commands the Bypass Valve to one of two positions - HOT EGR or COLD EGR, depending on engine operating conditions. Under normal to high engine load and temperature conditions the intake system requests COLD EGR and the bypass valve is commanded to the COLD EGR position. The exhaust flow is directed into the two EGR coolers in series and then to the EGR Valve. Under light load/idle conditions, the intake system requests HOT EGR and the bypass valve is commanded to the HOT EGR position. The exhaust flow is directed through the bypass pipe directly into the EGR valve to prevent fouling of the EGR coolers.

When the ignition is turned OFF, the EGR Cooler Bypass Valve executes its own clean and learn operation. The bypass valve switches from seat to seat several times, effectively cleaning the stem while learning the seat position. Certain environmental conditions, such as low temperature, may inhibit the clean and learn operation, so it may not occur during every ignition cycle.

The EGR Cooler Bypass Valve has an integral position sensor that feeds back to the ECM. The sensor is located on the output gear of the actuator and is a non-contacting type sensor. The ECM uses the position sensor to determine the position of the valve. The ECM sends a reference voltage through the 5-volt reference circuit to the position sensor. The ECM provides a voltage return path for the sensor through the low reference circuit. A variable voltage signal, based on the valve position, is sent from the sensor to the ECM through the position sensor signal circuit.

EGR Valve Control Enabling Conditions

Exhaust gas recirculation (EGR) valve control will only be enabled during idle and cruising conditions when the following conditions are met

1. The Intake Air Temperature (IAT) is greater than -5°C (23°F). EGR valve control will remain enabled until the IAT is less than -8°C (17.6°F). Once disabled the IAT must increase to greater than -5°C (23°F) before EGR valve control is re-enabled.
2. The IAT is less than 80°C (176°F). Once disabled the IAT must decrease to less than 70°C (158°F) before EGR valve control is re-enabled.

LML ECT Enable Thresholds for EGR Valve Control

LML ECT Disable Thresholds for EGR Valve Control

1. The ECT is greater than 45°C (113°F) (LGH applications only). EGR valve control will be disabled when ECT decreases to less than 41°C (106°F)
2. The ECT is less than 108°C (226°F) (all applications). Once disabled ECT must decrease to less than 105°C (221°F) before EGR valve control is re-enabled.
3. The Barometric Pressure (BARO) is greater than 74 kPa (10.7 psi). EGR valve control will remain enabled until the BARO is less than 72 kPa (10.4 psi). Once disabled the BARO must increase to greater than 74 kPa (10.7 psi) before EGR valve control is re-enabled.
4. The battery voltage is greater than 8.0 V.
5. No active air system faults are present.

Scheme 135

The diesel exhaust aftertreatment system is designed to reduce the levels of hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter remaining in the vehicle's exhaust gases. Reducing these pollutants to acceptable levels is achieved through a 3 stage process

1. A diesel oxidation catalyst (DOC) stage
2. A selective catalyst reduction (SCR) stage
3. A diesel particulate filter (DPF) stage

In stage 1, the DOC removes exhaust HC and CO through an oxidation process. After the stage 1 treatment, diesel exhaust fluid (DEF), also known as reductant or urea, is injected into the exhaust gases prior to entering the SCR stage. Within the SCR, NOx is converted to nitrogen (N2), carbon dioxide (CO2) , and water vapor (H20) through a catalytic reduction fueled by the injected DEF. In the final or stage 3 process, particulate matter consisting of extremely small particles of carbon remaining after combustion are removed from the exhaust gas by the large surface area of the DPF.

Scheme 136

1. NOx Sensor 1
2. EGT 1
3. Diesel Oxidation Catalyst (DOC)
4. EGT 2
5. Selective Catalyst Reduction (SCR)
6. EGT 3
7. NOx Sensor 2
8. Diesel Particulate Filter (DPF)
9. EGT 4
10. Exhaust Cooler
11. DPF Differential Pressure Sensor
12. Reductant Heater (3)
13. Reductant Pressure Sensor
14. Reductant Level/Temperature Sensor
15. Reductant Purge Valve
16. Reductant Pump
17. Reductant Injector
18. Hydrocarbon Injector (HCI)

Diesel Oxidation Catalyst (DOC) Operation

The DOC functions much like the catalytic converter used with gasoline fueled engines. As with all catalytic converters, the DOC must be hot in order to effectively convert the exhaust HC and CO into CO2 and H20. On cold starts, the exhaust gases are not hot enough to create temperatures within the DOC high enough to support full HC and CO conversion. The temperature at which full conversion occurs is known as light-off.

In addition to reducing emissions, the DOC also generates the exhaust heat needed by the SCR stage. Exhaust gas temperature (EGT) sensors are located upstream (EGT 1) and downstream (EGT 2) of the DOC. By monitoring the temperature differential between these two sensors, the ECM is able to confirm DOC light-off. Light-off is confirmed by a DOC output temperature that is greater than its input temperature.

In order to generate the high exhaust temperatures needed for regeneration, the aftertreatment system increases exhaust temperatures by injecting diesel fuel directly into the exhaust gases entering the DOC. This is accomplished by means of an ECM-controlled fuel injector, called the hydrocarbon injector (HCI), in the exhaust pipe upstream of the DOC. Injecting fuel directly into the exhaust rather than using a post-injection strategy greatly reduces oil/fuel dilution.

Proper DOC function requires the use of ultra-low sulfur diesel (ULSD) fuel containing less than 15 parts-per-million (ppm) sulfur. Levels above 15 ppm will reduce catalyst efficiency and eventually result in poor driveability and one or more DTCs being set.

Selective Catalyst Reduction (SCR) Operation

While diesel engines are more fuel efficient and produce less HC and CO than gasoline engines, as a rule they generate much higher levels of NOx. In order to meet today's tighter NOx limits, an SCR catalyst, along with DEF, is used to convert NOx into N2, CO2, and H2O.

The ECM uses two smart NOx sensors to control exhaust NOx levels. The first NOx sensor is located in the turbocharger outlet and monitors the engine out NOx. The second NOx sensor is located in the exhaust pipe downstream of the SCR and monitors NOx levels exiting the aftertreatment system. The smart NOx sensors communicate with the ECM over the serial data line. Similar to the way the ECM uses oxygen sensor signals to maintain an optimum air/fuel ratio under various loads in gasoline applications, the ECM uses exhaust oxygen and NOx data from the NOx sensors to maintain the desired air/fuel ratio and to calculate the amount of DEF required to reduce exhaust NOx levels.

The NOx sensors incorporate an electric heater to quickly bring the sensors to operating temperature. As moisture remaining in the exhaust pipe could interfere with sensor operation, the ECM delays turning on the heaters until the exhaust temperature exceeds a calibrated value. This allows any moisture remaining in the exhaust pipe to boil off before it can effect NOx sensor operation. Depending on engine temperature at start up, the delay can be less than a minute or as long as two minutes. Typically, NOx sensor 1 will reach operating temperature faster than NOx sensor 2 as it's closer to the engine's hot exhaust. At idle or low engine speeds, NOx sensor 2 may require up to 5 minutes to reach operating temperature. The sensors must be hot before accurate exhaust NOx readings are available to the ECM.

DEF is a mixture of 66% deionized water and 34% urea. Within the SCR, exhaust heat converts the urea into ammonia (NH3) that reacts with NOx to form nitrogen, CO2, and water vapor. Optimum NOx reduction occurs at SCR temperatures above 250°C (480°F). At temperatures below 250°C, the incomplete conversion of urea forms sulfates that can poison the catalyst. To prevent this poisoning, the ECM suspends DEF injection when exhaust temperature falls below a calibrated limit.

The 6.6L (LML) engine uses exhaust gas temperature management to maintain the SCR catalyst within the optimum NOx conversion temperature range of 200-400°C (390-750°F). The ECM monitors EGT sensors located upstream (EGT 2) and downstream (EGT 3) of the SCR in order to determine if the SCR catalyst is within the temperature range where maximum NOx conversion occurs. The 6.6L (LGH) engine does not use exhaust gas temperature management; the ECM calculates SCR temperature based on the engine speed and load. For LGH applications, SCR temperatures are typically at the lower end of the temperature range under normal driving conditions; however, SCR temperatures will increase when hauling a trailer.

The smart NOx sensors provide a serial data message to the ECM with information on exhaust oxygen levels.

Diesel Exhaust Fluid (DEF) System

The DEF system consists of the following components located at the DEF reservoir

1. An electrically-operated reductant pump (16)
2. A reductant purge valve (15)
3. A reductant pressure sensor (13)
4. A integrated reductant level sensor and reductant temperature sensor (14)
5. Reductant system heaters (12)

The remaining DEF system component, an electrically-controlled reductant injector (13), is external to the reservoir.

The on-board reservoir holds approximately 19 liters (5 gallons) of DEF. An ECM controlled pump within the reservoir supplies pressurized DEF to the reductant injector located upstream of the SCR. A smart DEF level sensor within the reductant reservoir sends the ECM a serial data message indicating DEF level. The DEF pressure sensor provides the ECM with a voltage signal proportional to the reductant pressure generated by the DEF pump. The ECM varies the duty-cycle of the pump voltage to maintain reductant pressure within a calibrated range.

The state of the reductant purge valve determines whether DEF from the reductant pump is directed to the reductant injector or returned to the reservoir. In the normally de-energized state, the reductant purge valve directs reductant from the pump to the reductant injector. When the ignition is turned OFF, the ECM energizes both the reductant purge valve and reductant pump for about 30 to 45 seconds in order to purge the supply line of DEF. The ECM also commands the reductant injector to 100% to prevent vacuum from forming during the purge process. Purging prevents the reductant from freezing in the pump or supply line to the reductant injector.

The ECM energizes the reductant injector to dispense a precise amount of reductant upstream of the SCR in response to changes in exhaust NOx levels. Feedback from NOx sensors 1 and 2 allow the ECM to accurately control the amount of reductant supplied to the SCR. If more reductant is supplied to the SCR than is needed for a given NOx level, the excess reductant results in what is called ammonia slip where significant levels of ammonia exit the SCR. Since the NOx sensors are unable to differentiate between NOx and ammonia, ammonia slip will cause NOx sensor 2 to detect higher NOx levels than actually exist.

Cold Weather Operation

As reductant will freeze at temperatures below 0°C (32°F), there are 3 reductant heaters. Reductant heater 1 is in the reductant reservoir, reductant heater 2 is in the supply line to the reductant injector, and reductant heater 3 is at the reductant pump. The ECM monitors the reductant temperature sensor located within the reservoir in order to determine if reductant temperature is below its freeze point. If the ECM determines that the reductant may be frozen, it signals the Glow Plug Control Module (GPCM) to energize the reductant heaters.

Reductant pump operation is disabled for a calibrated amount of time to allow the heaters time to thaw the frozen reductant. Once the thaw period expires, the ECM energizes the reductant pump to circulate warm reductant through the de-energized reductant purge valve and back to the reservoir to speed thawing. The ECM looks for an increase in the reductant temperature to verify that the reductant reservoir heater is working.

Scheme 137

The DPF captures diesel exhaust gas particulates, also known as soot, preventing their release into the atmosphere. This is accomplished by forcing particulate-laden exhaust through a filter substrate consisting of thousands of porous cells. Half of the cells are open at the filter inlet but are capped at the filter outlet. The other half of the cells are capped at the filter inlet and open at the filter outlet. This forces the particulate-laden exhaust gases (1) through the porous walls of the inlet cells into the adjacent outlet cells trapping the particulate matter. The DPF is capable of removing more than 90% of particulate matter, or soot carried in the exhaust gases.

Differential Pressure Sensor (DPS)

Pressure connections at the DPF inlet and outlet allow the differential pressure sensor (DPS) to measure the pressure drop across the filter. This pressure drop increases as trapped soot collects in the cells of the DPF during vehicle operation. The rate at which soot collects varies with the power demands placed on the engine. If left unchecked, the increasing backpressure will eventually result in a drivability problem.

Normal DPF Regeneration

Over time, the soot trapped on the cell walls acts to restrict exhaust flow through the DPF reducing its effectiveness as well as reducing engine efficiency. This restriction in exhaust flow produces a pressure drop across the DPF that increases as the once porous cell walls become saturated with trapped soot. A DPS monitors the pressure drop across the DPF and provides the ECM with a voltage signal proportional to soot buildup. Once soot buildup reaches a specified limit, as signaled by the increased pressure drop across the DPF, the ECM commands a regeneration event to burn-off the collected soot during normal vehicle operation. Regeneration events occurring during vehicle operation are known as normal regenerations as they occur automatically and without driver knowledge. In general, the vehicle will need to be operating continuously at speeds above 48 km/h (30 mph) for approximately 20-30 minutes for a full and effective regeneration to complete.

The frequency of normal DPF regeneration is a function of the engine run time, miles driven, and fuel consumed since the last regeneration event. To initiate a regeneration event, the ECM commands the HCI to inject additional fuel upstream of the DOC in order to create the additional exhaust heat necessary to promote regeneration and burn-off the collected soot.

During regeneration exhaust temperatures may exceed 550°C (1,022°F) due to the rapid catalytic combustion of soot within the DPF. Conversely, under low engine speed or light loads, exhaust temperatures may be too low to promote proper regeneration. To protect the DPF catalyst from thermal damage due to excessive soot combustion or from sulfate poisoning at low temperatures, the ECM monitors EGT sensors upstream and downstream of the DPF during regeneration. If the vehicle is slowed to idle speed during a normal DPF regeneration, the engine may maintain an elevated idle of 800 RPM until the DPF is cooled to a calibrated temperature.

Should the EGT sensors indicate that regeneration temperatures have exceeded a calibrated threshold, regeneration will be temporally suspended until the sensors return to a normal temperature. If regeneration temperatures fall below a calibrated threshold, regeneration is terminated and a corresponding DTC is set in the ECM.

Under most conditions, the soot collected within the DPF burns off during normal regeneration cycles. Periodic regeneration prevents the buildup of soot from reaching a level where its burn-off could produce damaging high temperatures within the DPF. Vehicles operated at prolonged low speed or low loads where normal regeneration does not occur will eventually reach a high soot load condition. When the increased pressure drop across the DPF is detected by the DPS, the ECM illuminates the DPF lamp in the instrument cluster and sends a Clean Exhaust Filter message to the driver information center (DIC). The owner manual diesel supplement describes how the vehicle should be driven in order to enable normal regeneration.

Service Regeneration

Should the vehicle operator fail to drive the vehicle within the conditions necessary to initiate a normal regeneration cycle, the ECM illuminates the Service Engine Soon lamp and displays a REDUCED ENGINE POWER message on the DIC once the soot buildup exceeds a calibrated value. The vehicle will remain in the reduced power model until service regeneration is performed.

Service regeneration is required because the amount of soot collected in the DPF, known as soot load, is too high to be burned off without possible thermal damage to the DPF's ceramic substrate.

Service regeneration is one of several output control functions available on the scan tool. When service regeneration is commanded, the ECM takes control of engine operation until the service regeneration is completed in about 35 minutes or until the service regeneration is either cancelled by the technician or is aborted by the ECM when it detects unexpected conditions. The ECM commands the HCI to inject additional fuel upstream of the DOC to burn off the soot.

The service regeneration can be terminated by applying the brake pedal, commanding service regeneration OFF using the scan tool, or disconnecting the scan tool from the vehicle.

Service Regeneration Precautions

Exhaust temperatures at the tailpipe may exceed 300°C (572°F) during service regeneration. Observe the following precautions

1. Service regeneration must be performed outdoors. Most exhaust removal hoses cannot withstand the high exhaust temperatures generated during regeneration.
2. Park the vehicle outdoors and keep people, other vehicles, and combustible material away during service regeneration.
3. Park the vehicle in an area that provides a clearance area of at least 10 feet on all sides of the vehicle and open the hood.
4. Ensure the tailpipe exhaust cooler is not obstructed by mud or debris.
5. Do not leave the vehicle unattended during service regeneration.

The ECM uses two EGT sensors to measure the temperature of the exhaust gases at the inlet (EGT 3) and outlet (EGT 4) of the particulate filter. Optimum particulate filter temperature is crucial for emission reduction and for ensuring complete regeneration. Excessive particulate filter temperatures could damage the ceramic substrate. The ECM monitors the inlet and outlet exhaust gas temperature sensors in order to maintain the particulate filter at its optimum temperature.

Intake Air (IA) Valve

The intake air (IA) valve is located upstream of the intake air heater, and is normally in the open position. The ECM commands the valve to close in order to precisely control combustion temperature control during DPF regeneration. The IA valve will ensure the temperature of the exhaust gas remains in an efficient range under all operating conditions. The IA valve system uses a position sensor located within the valve assembly to monitor the position of the valve. The IA valve uses a motor to move the valve to a closed position and spring tension returns it to the open position. The motor is operated through Motor Control 1 and Motor Control 2 circuits.

Exhaust Cooler

The exhaust system has been designed to lower tailpipe exhaust gas temperatures during regeneration. The exhaust cooler at the end of the tailpipe draws in cooler air as exhaust gases exit the tailpipe. Fresh air mixes with the hot exhaust gases reducing exhaust gas temperatures at the tailpipe outlet.

Ash Loading

Ash is a non-combustible by-product from normal oil consumption. Low Ash content engine oil (CJ-4 API) is required for vehicles with the DPF system. Ash accumulation will eventually cause a restriction in the DPF. Being non-combustible, ash is not burned off during regeneration. An ash loaded DPF will need to be removed from the vehicle and replaced.

Scheme 138

The fuel tank (5) stores the fuel supply. A mechanical fuel injection pump (13), located below the engine intake, includes the fuel supply pump and the high-pressure pump. Fuel is primed through an electric fuel priming pump (6) and is also drawn from the mechanical fuel supply pump through the diesel fuel conditioning module (8), which combines a water separator and filter element, then through a fuel filter vacuum switch (9) to the fuel injection pump. The engine control module (ECM) controls the fuel pump pressures by using two fuel pressure regulators, fuel pressure regulator 1 is located on top of the fuel injection pump and fuel pressure regulator 2 (7) is located on a fuel rail (2). The fuel pressure sensor (4) provides a voltage signal to the ECM to indicated fuel rail pressures. The high pressure fuel is supplied to the fuel injectors (1) through separate high pressure pipes. The fuel injectors supply fuel directly to the combustion chambers of the engine. The fuel that is not injected into the combustion chamber is used to help lubricate and cool the injector and is routed back to the fuel tank. The fuel injector return line pressure regulator (14) maintains fuel pressure on the return side of the fuel injectors. This is required for proper fuel injector operation. In the event the vehicle runs out of fuel a check valve (11) in the exhaust aftertreatment fuel injector (10) supply line opens and the fuel supply pump back fills the return side with fuel.

Scheme 139

The fuel tank stores the fuel supply. The fuel tank is located on the left side of the vehicle. The fuel tank is held in place by 2 metal straps (2) that attach to the frame. The fuel tank are molded from high density polyethylene.

Scheme 140

The fuel filler cap has a torque-limiting device that prevents the cap from being over tightened. To install , turn the cap clockwise until you hear audible clicks. This indicates that the cap is fully seated.

Scheme 141

The fuel sender assembly is mounted in the fuel tank and consists of a fuel strainer (2) and a fuel level sensor (1).

Fuel Strainer

The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment.

Fuel Level Sensor

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor card. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the amount of fuel in the fuel tank. The engine control module (ECM) sends the fuel level information via the class 2 circuit to the instrument panel cluster. This information is used for the instrument panel (I/P) fuel gauge and the low fuel warning indicator, if applicable. The ECM also monitors the fuel level input for various diagnostics.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

Fuel Pipe O-Rings

O-rings seal the connections in the fuel system. Fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.

Fuel Feed and Return Pipes

The fuel feed pipe carries fuel from the fuel tank to the fuel injector control module. The fuel return pipe carries fuel from the fuel rail assemblies back to the fuel tank. The fuel pipes consist of 2 sections

1. The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of steel with sections of rubber hose covered with braiding.
2. The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the fuel rail pipes. These pipes are constructed of steel with sections of rubber hose covered with braiding.

Scheme 142

The fuel conditioning module is located on the right side frame rail and consists of a fuel filter (1) and water in fuel sensor. Fuel from the tank or return line system is drawn through the conditioning module by the fuel injection pump. Some return line fuel from the fuel rail is cycled back through the conditioning module to heat the incoming fuel.

Fuel Filter

The paper filter element traps particles in the fuel that may damage the fuel injection system. A CHANGE FUEL FILTER will appear on the driver information center when a fuel filter change is required. The fuel filter life monitor uses two control paths consistent with driving conditions. The primary control is based on the accumulated fuel burned, and the secondary control is based on the fuel rail deviations and high pressure pump duty cycle. If the fuel has been contaminated with water or other contaminates, the monitor will see erratic system corrections and display the message or warning lamp. If the fuel filter is not changed when the message or warning light is displayed, then a fuel restriction could occur and cause other diagnostics to fail. The filter life monitor does not drive the diagnostics, but is a result of the restriction. You must reset the fuel filter life monitor after each fuel filter change. It will not reset itself. Resetting the filter monitor without changing the filter will cause the fuel filter monitor to be inaccurate until the next fuel filter change and reset.

Water in Fuel Sensor

The water in fuel sensor is a 3 wire sensor the monitors the presence of diesel and water. When water is present the ECM detects low voltage on the signal circuit and sends a serial data message to the instrument panel cluster to display the WATER IN FUEL SERVICE REQUIRED message.

Fuel Priming Pump

An electric fuel prime pump (2) supplies fuel to the low pressure fuel system. The fuel pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. This fuel pump is powered by the fuel pump relay that is controlled by the engine control module (ECM). The pump is part of the diesel fuel conditioning module assembly. The module assembly is located under the vehicle forward of the fuel tank.

Fuel Filter Pressure Switch

The fuel filter pressure switch is a normally closed switch located next to the fuel conditioning module. If fuel supply line vacuum reaches greater than 14 in Hg the switch will open. The engine control module (ECM) monitors the voltage on the fuel filter pressure switch signal circuit and will send a serial data message to the instrument panel cluster to display the FUEL FILTER RESTRICTED message.

Fuel Temperature Sensor 1

The fuel temperature sensor 1 is a thermistor that is located in the back of the fuel injection pump. The ECM monitors the fuel temperature sensor signal circuit in order to calculate the temperature of the fuel entering the engine fuel rail.

Fuel Temperature Sensor 2

The fuel temperature sensor 2 also referred as the fuel rail temperature sensor, is a thermistor that is located in the return line near the quick-connect fittings. The ECM monitors the fuel rail temperature sensor signal circuit in order to calculate the temperature of the fuel leaving the engine fuel rail.

Scheme 143

The high pressure fuel pump (4) is a mechanical high pressure pump. The high pressure fuel pump is located below the intake manifold. Fuel is pumped to the fuel rails at a specified pressure. Fuel pressure is regulated by a valve on the inlet of the fuel pump and one on the fuel rail, both are controlled by the engine control module (ECM). Excess fuel from the high pressure fuel pump returns to the fuel tank through the fuel return pipe.

Exhaust Aftertreatment Fuel Injector

The exhaust aftertreatment fuel injector, also known as the indirect fuel injector is located on the right side cylinder head. The exhaust aftertreatment fuel injector is used to inject fuel into the exhaust system to generate the required heat needed by the diesel oxidation catalyst to function properly and helps to extend engine oil life.

Fuel Rail and Pipes

The left and right fuel rail assemblies attach to the cylinder heads. The fuel rail assemblies distribute pressurized fuel to the fuel injectors through the fuel lines.

Fuel Rail Pressure Sensor

The fuel rail pressure sensor in located in the back of the left side fuel rail assembly. The fuel rail pressure sensor provides the engine control module (ECM) an indication of the actual fuel rail pressure. The ECM uses this information to regulate the fuel pressure, by commanding the fuel pressure regulators to obtain the desired fuel pressure.

Fuel Pressure Regulator 1

The engine control module (ECM) controls the fuel rail pressure using two pulse width modulated fuel rail pressure regulators. Fuel pressure regulator 1 is located on the fuel injection pump and meters the amount of fuel that enters the high pressure side of the pump. From the high pressure pump, the fuel moves to the fuel rail through a high pressure metal line. The fuel rail distributes high pressure fuel to all 4 fuel injectors.

The ECM controls fuel pressure in three different operating modes. The ECM commands fuel pressure regulator 2 to control fuel pressure at idle and commands fuel pressure regulator 1 to control fuel pressure when engine speeds are above 1700 RPM. Under certain conditions both regulators are used to control fuel pressure.

Scheme 144

The engine control module (ECM) controls the fuel rail pressure using two pulse width modulated fuel rail pressure regulators. Fuel pressure regulator 2 is located on the end of the fuel rail and meters the amount of fuel being returned to the fuel tank. The ECM varies the pulse width modulated voltage to the fuel pressure regulator 2 to relieve excessive fuel pressure which returns to the fuel tank. When the ignition is OFF, fuel pressure regulator 2 opens to bleed off the pressure in the fuel rail.

The ECM controls fuel pressure in three different operating modes. The ECM commands fuel pressure regulator 2 to control fuel pressure at idle and commands fuel pressure regulator 1 to control fuel pressure when engine speeds are above 1700 RPM. Under certain conditions both regulators are used to control fuel pressure.

Fuel Injectors

The fuel injectors are located above each cylinder and deliver fuel directly into the cylinder. Each injector has a high pressure fuel pipe from the fuel rail and a return line.

The engine control module (ECM) supplies a high voltage supply circuit and a high voltage control circuit for each fuel injector. The injector high voltage supply circuit and the high voltage control circuit are both controlled by the ECM. The ECM energizes each fuel injector by grounding the control circuit and supplying each fuel injector with up to 250 V and 20 amps on the voltage supply circuit to activate the Piezo type fuel injectors. This is controlled by boost capacitors in the ECM. During the 250 V boost phase, the capacitor is used to charge the injector piezo stack, allowing for injector opening. The injector is then held open with this high voltage. At the end of the injection event the ECM closes the injector by discharging the injector piezo stack.

Return Line Pressure Regulator

The fuel injector return line pressure regulator maintains 4-11 bar (58-158 psi) of fuel pressure on the return side of the fuel injectors. This is required for proper fuel injector operation. This return side pressure also supplies the indirect fuel injector with fuel during engine operation. In the event the vehicle runs out of fuel a check valve in the return line opens and the fuel supply pump back fills the return side with fuel.

Glow Plug Operation

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the instant start system glow plugs is accomplished by a glow plug control module and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the glow plug control module within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.

A normal functioning system operates as follows

1. Turn the ignition ON with the engine OFF, and at room temperature.
2. The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.
3. The glow plug wait lamp is ON for 1 second during cold start.
4. The glow plug wait lamp may not illuminate during a warm engine start.
5. If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

The glow plug control module provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

Intake Air Heater

The glow plug control module controls and monitors the intake air heater. The ECM sends commands to the glow plug control module to enable or disable the intake air heater when certain conditions met. The glow plug control module monitors the voltage and feedback circuits of the intake air heater to verify proper operation.

Diesel Exhaust Fluid (DEF) Heater Control

The glow plug control module supplies and monitors voltage to the 3 Diesel Exhaust Fluid heaters. The engine control module (ECM) requests any or all of the heaters to be on depending on ambient temperature. The glow plug control module will disable diesel exhaust fluid heater requests from the ECM during glow plug operation.

SmartNOx Boost

The glow plug control module provides a constant voltage to the SmartNox sensors to ensure proper sensor operation. The glow plug control module has internal voltage boosting circuits that will draw more current from the battery when system voltage is low and supply a higher voltage to the SmartNOx sensors in order to maintain proper operation.

The intake air heater is an electric heating element that heats the air as it is drawn into the engine intake manifold during cold weather operation. The glow plug control module controls and monitors the intake air heater control circuits. The engine control module (ECM) sends commands to the glow plug control module to enable or disable the intake air heater when certain conditions met. The glow plug control module monitors the voltage and feedback circuits of the intake air heater to verify proper operation.

A normal functioning system operates as follows

1. Engine coolant temperature is below 40°C (104°F).
2. Barometer pressure, engine coolant temperature, engine run time, and battery voltage are calculated by the ECM to determine the required duty cycle of the intake air heater.
3. The engine control module (ECM) will send a serial data message requesting intake air heater operation to the glow plug control module.
4. The intake air heater receives the ON command from the glow plug control module and current flows through the heater element.
5. The intake air heater will stay energized for up to 700 seconds or until the intake air temperature reaches 29.8°C (85°F).
6. The ECM monitors the engine coolant temperature and once the temperature is above 49.9°C (121°F), the ECM sends a signal to the glow plug control module to turn OFF the intake air heater.

Manual High Idle

The diesel engine has a high idle system to improve the warm-up time of the engine in cold weather conditions. This system allows the engine control module (ECM) to increase the idle speed above the normal calibrated value. The ECM increases the idle speed using the following adjustments

1. The fuel injection timing is changed
2. The fuel injection quantity is changed
3. The turbocharger vane position is commanded closed-The vane position will be farther closed than any other normal operating condition.

The instrument panel will indicate the high idle system is active one of two ways

1. The driver information center (DIC) will indicate an active high idle.
2. The manual high idle feature comes enabled from the factory. The Elevated Idle function in the scan tool will disable or enable this feature. If the engine does not increase to the calibrated high idle speed after the procedure is performed, use the scan tool to verify the Elevated Idle speed feature is enabled.

Manual High Idle Speed Enable and Disable

To enable or disable the manual high idle system perform the following procedure

1. Turn the ignition ON, with the engine OFF.
2. Depress the accelerator pedal to the floor and hold down.
3. While the accelerator pedal is depressed, depress the brake pedal 3 times in less than 8 seconds.
4. Release the accelerator pedal.
5. Start the engine.

When the procedure is followed the engine idle speed will slowly increased to the calibrated high idle speed of 1,200 RPM.

The idle speed will return to normal if any of the following conditions occur

1. There is brake, clutch, or throttle input from the driver.
2. The automatic transmission is shifted out of Park or Neutral.
3. The air temperature is more than 7°C (45°F).
4. The engine coolant temperature (ECT) is more than 68°C (154°F).
5. The vehicle speed exceeds 0 km/h (0 mph).

The high idle system will reactivate automatically when the following conditions occur

1. The engine has been idling for more than 30 seconds.
2. The transmission is placed in Park or Neutral.
3. The vehicle speed is 0 km/h (0 mph).
4. The ambient air temperature is less than 3°C (37°F).
5. The ECT is less than 68°C (154°F).
6. The brake, clutch and throttle pedals are not depressed.

Scheme 145

Scheme 146

The turbocharger increases engine power by pumping compressed air into the combustion chambers, allowing a greater quantity of fuel to combust at the optimal air/fuel ratio. The turbine spins as exhaust gas flows out of the engine and over the turbine blades, and turns the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.

The ECM controls the turbocharger vanes. The vanes are used to vary the amount of boost pressure and can control the boost pressure independent of engine speed. The vanes mount to a unison ring which is rotated to change the vane angle. The ECM will vary the vane angle which adjusts the boost dependent upon the load requirements of the engine.

The turbocharger vanes are normally open when the engine is not under load. However, the ECM will often close the turbocharger vanes to create back pressure to drive exhaust gas through the Exhaust Gas Recirculation (EGR) valve as required. At extreme cold temperatures, the ECM may close the vanes at low load conditions in order to accelerate engine coolant heating.

The turbocharger is also utilized as a component of the exhaust brake system, if equipped. Under certain conditions, the ECM will automatically close the turbocharger vanes to build back pressure in the exhaust, which reduces engine speed and slows the vehicle without applying the brakes.

During regeneration, the ECM will vary the turbocharger vanes to assist with the exhaust system warm-up, and to maintain proper engine exhaust temperatures needed to properly regenerate the Diesel Exhaust Particulate Filter (DPF).

The turbocharger control system utilizes the following components

Turbocharger Vane Position Control Solenoid Valve

The vane position control solenoid valve (2) works in conjunction with oil pressure to control the turbocharger vanes. The ECM uses a pulse width modulation on both control circuits to control the solenoid valve. The solenoid valve allows the engine oil pressure to move a piston. This piston rotates the unison ring, thus controlling the engine boost dependent upon engine load.

Turbocharger Vane Position Sensor

The ECM uses the turbocharger vane position sensor to monitor the turbocharger vane angle. The voltage is low when the vanes are open and high when the vanes are closed.