The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis.

The Engine Cranks But Does Not Run diagnostic table assumes the following:

If the cause of an engine cranks but will not run condition has not been found, inspect for the following conditions:

The numbers below refer to the step numbers on the diagnostic table.

The Fuel Rail Pressure Regulator graphing procedure offers valuable information on regulator performance by comparing desired and actual fuel rail pressure. An almost perfect comparison between actual rail pressure and desired rail pressure is found on a fairly new, low mileage engine. A minor ripple is acceptable behavior for the fuel rail pressure regulator and is seen on high mileage engines. A "shark tooth" fluctuation in actual fuel rail pressure indicates a sticking pressure regulator.

An electric fuel pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel pump is powered by the fuel pump relay. The fuel pump relay is controlled by the engine control module (ECM). The ECM enables the fuel pump when the ignition is turned ON, and will continue to run for a while, or until the engine starts. If the ignition is left in the ON position, the pump will run for about four seconds. The ECM will also turn OFF the fuel pump if incorrect voltage is detected on the control circuit. The ECM will need to be powered down with a key cycle during diagnosis or after repairs, before it will command the fuel pump ON again.

The following conditions may cause the fuel pump fuse to open:

Fuel is drawn by the supply pump through a pre-filter screen in the tank and to the engine through the fuel supply lines. The fuel passes through the fuel filter/heater element housing, which combines a water separator, fuel heater element and a filter element. The fuel is then delivered to the high-pressure fuel injection pump. Scan tool output control function or repetition of ignition key ON/OFF is used to prime the fuel system after changing the fuel filter or servicing the fuel system by activating the fuel pump without engine running. If the fuel system is not supplying enough fuel, a driveability concern may occur. If air is being drawn into the fuel injection system, a Cranks But Will Not Run or Hart Start symptom could exist.

The fuel injection pump is engine-driven by the timing belt. From the high-pressure fuel injection pump, the pressurized fuel flows to the common rail. Common rail supplies pressurized fuel to the fuel injectors. The fuel rail pressure (FRP) sensor is mounted on the common rail.

The fuel return system routes fuel from the fuel injectors, fuel rail, and the fuel injection pump. The fuel pressure regulator is located in the common rail. The return fuel travels to the fuel tank. If the high side fuel pressure becomes excessive, the fuel pressure regulator releases the fuel into the fuel return system.

The following conditions may cause an air leak into the fuel supply system:

Fuel is drawn by the supply pump through a pre-filter screen in the tank and to the engine through the fuel supply lines. The fuel passes through the fuel filter/heater element housing, which combines a water separator, fuel heater element and a filter element. The fuel is then delivered to the high-pressure fuel injection pump. Scan tool output control function or repetition of ignition key ON/OFF is used to prime the fuel system after changing the fuel filter or servicing the fuel system by activating the fuel pump without engine running. If the fuel system is not supplying enough fuel, a driveability concern may occur. If air is being drawn into the fuel injection system, a Cranks But Will Not Run or Hart Start symptom could exist.

The fuel injection pump is engine-driven by the timing belt. From the high-pressure fuel injection pump, the pressurized fuel flows to the common rail. Common rail supplies pressurized fuel to the fuel injectors. The fuel rail pressure (FRP) sensor is mounted on the common rail.

The fuel return system routes fuel from the fuel injectors, fuel rail, and the fuel injection pump. The fuel pressure regulator is located in the common rail. The return fuel travels to the fuel tank. If the high side fuel pressure becomes excessive, the fuel pressure regulator releases the fuel into the fuel return system.

Bent or pinched fuel return lines on the engine can cause a restricted fuel return flow.

When conditions arise in cylinder balancing, a scan tool output control test function is provided to help in locating the cause. A compression test can be used to decide whether the cause should be attributed to the engine or the injection system. Once the problem has been limited to the injectors, further tests can determine which injector is responsible for the condition in cylinder balancing.

The test consists of 3 modes (A, B, C), which are conducted in different test conditions.

Using a scan tool, perform the compression tests following the instructions displayed on the screen.

Mode A: Output of rotational speeds of selected cylinders during a compression test

All injections are inhibited in order to allow a compression test by actuating the starter without starting the engine. The rotational engine speed at each top dead center (TDC) is provided. A lower cylinder selective engine speed in compression to the others shows a higher compression of this cylinder. A higher cylinder selective engine speed a lower compression. The fuel balancing control (FBC) correction values in this test are zero. Note that the purpose of the test is to see the relative performance of each cylinder. The higher or the lower compression mentioned here does not necessarily mean that the actual engine cylinder compression performance as a gauge pressure is showing a same property.

Mode B: Quantity correction output by selected cylinder

In this test mode, the engine is running with the fuel balancing control (FBC) correction values enabled. The correction quantity shows an offset, which is added to the injected quantity to establish a vibration-free running of the engine. The cylinder selective engine speed is also provided. A higher cylinder balancing quantity correction shows an injector, which needs more time to inject an amount of fuel to produce the requested torque.

Mode C: Output of rotational speeds of selected cylinders for shut off cylinder balancing quantities

In this test mode, the engine is running with the fuel balancing control (FBC) correction values disabled. The cylinder selective engine speed is provided and the engine running behavior without FBC values can be monitored..

Fungi and other microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system. These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated, when service station tanks are being filled, fungi are distributed throughout the tank and may be pumped into a vehicle.Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom is fuel filter plugging, however various metal fuel system components including fuel sender assembly, pipes, fuel injectors, and fuel injection pump can corrode.

Caution: Avoid physical contact with the biocides in order to avoid personal injury.

If fungi have caused fuel system contamination, use a diesel fuel biocide to sterilize the fuel system. Do not exceed the dosage recommended on the label. Discontinue the use of a biocide when towing a trailer. It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing.

Steam cleaning may be necessary if most of the fungus growth cannot be removed with biocides.

The presence of water or gasoline in diesel fuel may also cause injection pump and fuel injector damage.

This procedure checks for the presence of water and gasoline in diesel fuel that may cause fuel injection pump and fuel injector damage.

Remove and inspect the fuel filter.

The fuel manager/filter assembly consists of the fuel heater, the water-in-fuel sensor, and a filter. The filter contains the coalescer, the device that combines small droplets of water into larger ones, and the filter/separator.

As the fuel enters the filter, the fuel passes through the fuel heater. The heater contains a thermostatic switch that opens or closes to turn the heater OFF or ON, depending on the temperature of the fuel.

The fuel then passes through the filter and the water coalescer, where the droplets of water in the fuel combine into larger drops that fall into the water reservoir in the filter. When fuel flows from the fuel manager/filter assembly to the high pressure pump, the fuel is clean and free of water.

The fuel heater is operated by the ECM. The fuel temperature sensor is a negative temperature coefficient (NTC) thermistor and sends the fuel temperature information to the ECM.

This table identifies which serial data link that a particular module uses for in-vehicle data transmission. Some modules may use more than one data link to communicate. Some modules may have multiple communication circuits passing through them without actively communicating on that data link. This table is used to assist in correcting a communication malfunction.

The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following:

The scan tool will power up with the ignition OFF. Some modules however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.

The number below refers to the step number on the diagnostic table.

The GMLAN serial data circuits are controller area network (CAN) high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. On this vehicle there are 2 utterly different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications. The vehicle theft deterrent (VTD) module and ECM exchange information using the BCM as the gateway module allowing communication between the high and low speed serial data busses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial data buss uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits.

The GMLAN serial data circuits are controller area network (CAN) high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. On this vehicle there are 2 utterly different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate.

The following items are required to be input when re-programming an ECM (ECM is not replaced):

The replacement of some components will require a setup procedure for complete repair.

The following setup procedures are required to be performed when replacing components:

If a vehicle is returned to service with either an active or inactive DPF related DTC, a function is available in the software that allows a scan tool to initiate a controlled regeneration to help pinpoint the components requiring repair. In addition, if the soot loading level has increased past maximum threshold and triggered power-reduction and regeneration inhibition, the service mode is the only way to regenerate the DPF and remove the power-reduction (service mode ignores many of the abort conditions required for normal driving regeneration). The service mode is also useful to validate that any repairs to the DPF system have been successful.DPF diagnostics are active during service regeneration, so checking for DPF DTCs during the service regeneration will help determine if any issues are present. If any DTCs occur, repair the issue and rerun the service mode.