Silverado 4500HD, 5500HD, 6500HD Powertrain Operation

The new 2019 Chevrolet Silverado 4500HD, 5500HD, 6500HD chassis cab models are equipped with a standard 6.6L Duramax diesel V8 engine (RPO L5D) and Allison 6-speed automatic transmission. (Fig. 8)

Fig. 8


The turbocharged 6.6L Duramax diesel V8 engine (RPO L5D), which is closely related to the L5P Duramax diesel, but is equipped with a smaller turbocharger and different Engine Control Module (ECM) calibrations. The engine block uses a deep skirt design for increased rigidity while the light-weight aluminum cylinder heads quickly dissipate heat. The four valves per cylinder and ports have a high swirl design to improve combustion.

Depending on the vehicle, the Duramax diesel is paired with one of the following 6-speed transmissions on 2WD and 4WD applications:

  • Allison 1700 with double overdrive
  • Allison 1750 with double overdrive
  • Allison 2700 with double overdrive


Glow Plugs

The engine uses eight ceramic glow plugs. Compared to conventional glow plugs, ceramic glow plugs enable greater efficiency through higher temperature capability and faster preheating time. However, ceramic glow plugs are much more sensitive to damage than conventional glow plugs. As a result, ceramic glow plugs are considered one-time-use. Anytime a ceramic glow plug is removed from the cylinder head, be sure to discard it and install a new glow plug. If the cylinder head is ever removed with the ceramic glow plugs, the ceramic glow plugs must all be replaced with new plugs.

When installing a new ceramic glow plug, clean the glow plug bore. Carbon build-up in the glow plug bore can damage the ceramic glow plugs.


Fuel System

The engine features direct injection with a high-pressure common rail system. High pressure fuel is controlled by the ECM, Fuel Pressure Regulator 1 and Fuel Pressure Regulator 2.

Dual fuel tanks are optional. Each tank must be filled through its own fill port. A fuel transfer pump is located in the secondary fuel tank to transfer fuel to the primary tank. The primary fuel tank contains a 3–phase electric fuel pump that is controlled by the fuel pump driver control module and ECM.


Exhaust Aftertreatment System

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 exhaust gases. The Diesel Oxidation Catalyst (DOC) removes exhaust HC and CO through an oxidation process. Particulate Matter (PM), consisting of extremely small particles of carbon remaining after combustion, are removed from the exhaust gas by the porous barrier in the Diesel Particulate Filter (DPF), which lets the gases pass through and retains the particulates. Diesel Exhaust Fluid (DEF) is injected into the exhaust gases prior to entering the Selective Catalytic Reduction (SCR). Within the SCR, NOx is converted to nitrogen (N2) and water vapor (H2O) through a catalytic reduction fueled by the injected DEF.

Occasionally, the DPF must be cleaned through a regeneration process. The frequency of normal DPF regeneration is determined by soot accumulation using the pressure drop across the DPF and engine run time, which is approximately 18 hours. The L5D diesel engine does not utilize a Hydrocarbon (HC) Injector, so in order to initiate a normal DPF regeneration event, the ECM commands additional post injection diesel fuel in order to create the additional exhaust heat in the DOC necessary to promote regeneration and burn-off the collected soot in the DPF.

If the vehicle is not operated 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 Engine Power mode until service regeneration is performed.

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. A service regeneration is completed in approximately 35 minutes. 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.


Diesel Exhaust Fluid

The DEF fill is located on the right fender behind the front wheel for easy fluid refills. (Fig. 9)

Fig. 9


The DEF system includes an electrically-operated DEF pump, an integrated DEF level sensor and DEF temperature sensor, a DEF control module, a DEF quality sensor and DEF system heaters.

The DEF tank holds approximately 7 gallons (26 liters) of DEF. A pump within the reservoir supplies pressurized DEF to the DEF injector located upstream of the SCR. A DEF level sensor within the DEF reservoir provides the DEF control module a signal indicating DEF level.

When the ignition is turned OFF, the DEF pump will run in reverse for about 45 seconds in order to purge the supply line of DEF. There is a one minute delay between ignition OFF and the start of purge to allow the exhaust system to cool in order to prevent hot exhaust gas from being drawn into the DEF line.


DEF in Cold Weather

A 32.5% solution of urea with 67.5% deionized water will begin to freeze at 12°F (−11°C). The freezing and thawing of DEF will not cause degradation of the product. There are two DEF heaters in the system. DEF Heater 1 is in the DEF reservoir and DEF Heater 2 is in the supply line to the DEF injector. If the DEF control module determines that the DEF may be frozen, it energizes the DEF heaters. DEF pump operation is disabled for a calibrated amount of time to allow the heaters an adequate amount of time to thaw the frozen DEF. The ECM looks for an increase in the DEF temperature to verify that the DEF reservoir heater is working.


DEF Level

The DEF level must be maintained for the vehicle to run properly. As the DEF level becomes low, warnings are displayed on the Driver Information Center. (Fig. 10) As the tank nears empty, vehicle speed will be limited in a series of steps. At least two gallons (7.57L) of DEF must be added to release the speed limitation.

Fig. 10


When there is an issue with the DEF such as a low fluid level or fluid contamination, the DEF Warning Light will illuminate, a DIC message will display and a chime will sound. To avoid vehicle speed limitations, fill the DEF tank at the first opportunity after a Low Fluid Level warning message displays.


Engine Oil

Engine oil with the letters CJ-4 or CK-4 are required for the Duramax diesel engine. Use SAE 15W-40 viscosity grade engine oil or, when outside temperatures are below 0°F (−18°C), use SAE 5W-40 to improve cold starting. The 6.6L engine Oil Capacity with Filter is 10 qt (9.5L).

The engine features a cold temperature high idle feature that elevates the engine idle speed from base idle to 1050–1100 RPM when outside temperatures are colder than 32°F (0°C), and the engine coolant temperature is colder than 150°F (65°C). By increasing the engine coolant temperature faster, this feature enhances heater performance.


PTO Option

A Power Take-Off (PTO) option is available for running add-on equipment, such as salt spreaders, snow plows, winches, and lift buckets. The PTO system controls engine speed to values higher than normal base idle, PTO load relay engagement, and remote starting and shutdown of the engine. When installing PTO aftermarket equipment, be sure to follow the PTO wiring and operation recommendations in the appropriate Service Information and GM Upfitter documentation. Upfitter Integration Bulletin UI120F covers PTO set-up on the vehicle.


Powertrain Warranty

The GM Powertrain warranty on the Silverado 4500HD, 5500HD and 6500HD trucks excludes the Allison transmission and Transmission Control Module (TCM). Investigate Vehicle History (IVH) will display this as: Powertrain Ltd. Wty. (Excludes Trans). The Allison Transmission and TCM are be warranted by Allison and must be taken to an Allison Authorized Distributor and Dealer Location for repair or replacement. Questions about the transmission warranty should be directed to your dealership’s Medium-Duty Service Representative.


– Thanks to Bob Briedis and Sherman Dixon

New Chevrolet Silverado 4500HD, 5500HD, 6500HD Take on Medium-Duty Market
Requesting GM Upfitter Technical Assistance

One Comment

  1. Jesus Vasquez says:

    How do you bleed air in radiator coolant system on Chevy Silverado 5500 diesel