Low Cab Forward Medium-Duty Trucks

The all-new Low Cab Forward medium-duty trucks are the latest in a long line of Chevrolet models in the commercial market. (Fig. 1) The seven new Low Cab Forward models, offered in regular cab or crew cab body styles, are the 3500, 3500HD, 4500, 4500HD, 4500XD, 5500HD and 5500XD. The trucks area available with a variety of upfit equipment and bodies provided by independent suppliers.


F01 LCF trucks 1

Fig. 1


Depending on the model, the trucks are equipped with either a GM 6.0L V8 gasoline engine, a GM 6.0L V8 LPG/CNG-capable engine, or an Isuzu 3.0L or 5.2L I4 turbocharged diesel engine.




3500 and 4500 Configurations


Available in regular cab and crew cab configurations, the 3500 and 4500 models are equipped with a Vortec 6.0L V8 engine (RPOs L96, LC8) and mated to a Hydra–Matic 6L90 6-speed automatic transmission (RPO MYD).


3500HD Configuration


The 3500HD truck is equipped with an Isuzu 3.0L I4 turbocharged engine (RPO IZ3) and an Aisin A460 6-speed automatic transmission (RPO IX0). It’s available in a regular cab configuration.


4500HD and 4500XD Configurations


The 4500HD and 4500XD models are equipped with an Isuzu 5.2L I4 turbocharged engine (RPO I1B) with an Aisin A465 6-speed automatic transmission (RPO IR7). These models are available in regular cab and crew cab configurations.


5500HD and 5500XD Configurations


The 5500HD is available in regular cab and crew cab configurations while the 5500XD is available as a regular cab model. These trucks are equipped with an Isuzu 5.2L I4 turbocharged engine (RPO I1B) and an Aisin A465 6-speed automatic transmission (RPO IR7).




Regular cab models equipped with 6.0L V8 gasoline or LPG/CNG engines – The engine oil dipstick can be found on the left side of the engine after tilting the cab.


Crew cab models equipped with 6.0L V8 gasoline or LPG/CNG engines – The engine oil dipstick is under the engine inspection sub-cover underneath the passenger seat. Use the strap on the front of the seat to raise the seat cushion. Release the sub-cover catch hooks to raise the cover for access to the oil dipstick.


Regular and crew cab models equipped with 3.0L I4 or 5.2L I4 diesel engines – The engine oil level can be checked using the oil level switch on the left side of the instrument panel. (Fig. 2) When checking the oil level, be sure the vehicle is on level ground and the engine is cool. Press the engine oil level check switch on the instrument panel. If the oil level is low, the red oil pressure warning light will turn on. If the engine oil level is acceptable, the green oil level indicator will turn on. The oil level also can be checked using the oil level dipstick.


F02 LCF button 3

Fig. 2




Diesel Engine Coolant


The diesel engines use a long-life coolant that is green in color. The addition of conventional green propylene glycol coolant will damage the engine. The factory-installed long-life green engine coolant is not available from GM Customer Care and Aftersales. Use only yellow long-life coolant (GM P/N 12378560; ACDelco P/N 10-5034) in the Low Cab Forward diesel engines. It is the only product that has been certified as compatible with the original long-life green diesel engine coolant.


A fuel system cooler (Fig. 3) has been added to models equipped with the 5.2L I4 diesel engine. The fuel system cooler compensates for increased fuel pressure and increased cylinder pressure due to changes in the camshaft timing, which results in higher fuel temperatures. The cooler reduces the fuel temperature prior to the fuel returning to the fuel tank. The cooler is mounted in front of the rear axle.


F03 LCF cooler 5

Fig. 3


Diesel Emission Systems


The 3.0L and 5.2L diesel engines use a Diesel Particulate Filter (DPF) system with a Diesel Oxidizing Catalyst (DOC) and a Selective Catalytic Reduction (SCR) assembly to meet current diesel emissions standards. (Fig. 4)


F04 LCF emission sys 6

Fig. 4


The DPF system that is designed to capture particulate matter (PM), or soot, is the same on both diesel engines except that the 3.0L system does not have a DPF fuel injector in the exhaust system for regeneration. The 3.0L system uses post injection from the main injectors during a DPF regeneration event instead of a DPF fuel injector.


Diesel Exhaust Fluid


The Diesel Exhaust Fluid (DEF) tank is installed on the frame on the left side of the vehicle. It includes a Level & Temperature Sensor, a drain plug and a tamper-resistant filler insert to prevent filling with fluids other than DEF. A visual DEF level gauge is helpful when filling the tank. (Fig. 5) The internal pickup includes the Coolant Heating Tube and Gauge Sending Unit. The pickup is serviced as a complete assembly.


F05 LCF DEF tank 7

Fig. 5


The DEF gauge (Fig. 6) on the instrument cluster indicates the quantity of DEF remaining in the DEF tank. When only one green bar is showing, the DEF tank is almost empty and should be refilled soon. If the vehicle is driven too long with only one bar, the green will change to amber and additional warnings and indicators will display. Vehicle speed will be severely limited when the DEF tank is empty.


F06 LCF DEF gauge 8

Fig. 6


The DEF indicator lamp on the instrument cluster will illuminate if there is a malfunction of the SCR system, the DEF level is too low or empty, of the DEF tank is refilled with any fluid other than DEF.




Vehicle Pigtail Connector


The Low Cab Forward trucks use the vehicle pigtail connector as the communication gateway (similar to the Diagnostic Link Connector, or DLC, on other GM vehicles) from which a Vehicle Health Report can be downloaded. The connector is accessible after removing the relay fuse cover in the center of the lower dash panel. Behind the panel, the connector is located in the lower right corner of the opening. It has a green identifying mark under the clear plastic cover.


Connect the RS232 Cable (Fig. 7, #2), which is an essential tool, to the vehicle pigtail connector (Fig. 7, #1) and to a laptop USB port with GDS 2 installed. Once connected, the Vehicle Health Report can be downloaded. The ignition must be on with the engine off throughout the download procedure. Two blue lights on the RS232 cable will flash while the download is in process.


F07 LCF pigtail connector 9

Fig. 7




There are currently 90 service tools that a dealership may need for this program. However, each dealership’s actual tool cost and/or need is dependent on their current tool inventory. In addition, nine of the service tools are available through the Loan Tool Program.


For additional information on the Low Cab Forward medium-duty trucks, refer to Bulletin #16-NA-337.


– Thanks to Bob Briedis


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  1. The long-life coolant (GM P/N 12378560; ACDelco P/N 10-5034) is day-glow yellow. The truck is built with green coolant, but it should be serviced with the yellow coolant (12378560).