14 Troubleshooting

In addition to operating the engine carefully and maintaining it properly, make sure to correct any malfunction promptly.

When the electronic engine control system detects a fault, it broadcasts a message on the datalink. The dash display will show the code "Motor Control Module (MCM) 128," indicating there is an engine fault.

Important: To read the complete fault code, bring the vehicle to an authorized dealer. Complete fault codes can be read using the Nexiq DDR or DDDL 7.0 version or later.

For fault codes and their meanings, see the next section in this guide.

The tables that follow are designed to identify the causes of common problems, suggest further checks and appropriate remedies. When dealer service is necessary, this is mentioned in the table.

Note : Remember to follow all cautions when troubleshooting the engine.

Problem - The Engine Will Not Crank
Cause	Remedy
The batteries are damaged or weak.	Test the batteries. Replace them, if needed.
The ignition switch is damaged.	Replace the ignition switch.
The battery cables are damaged and/or corroded.	Replace the battery cables.
The starter is damaged and/or worn.	Have an authorized repair facility replace the starter.
The clutch or transmission is damaged.	Bring the vehicle to an authorized repair facility for service.
There is internal damage to the engine.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Turns Over Slowly
Cause	Remedy
The batteries are damaged or weak.	Test the batteries. Replace them, if needed.
The ignition switch is damaged.	Replace the ignition switch.
The battery cables are damaged and/or corroded	Replace the battery cables.
The starter is damaged and/or worn.	Have an authorized repair facility replace the starter.
The engine oil does not meet the correct specifications.	Change the engine oil, using the correct type of oil.
The transmission fluid does not meet the correct specifications.	Change the transmission fluid, using the correct type of fluid.

Problem—The Engine Cranks, But Won't Start
Cause	Remedy
The batteries are damaged or weak.	Test the batteries. Replace them, if needed.
The cranking speed is not set correctly.	Bring the vehicle to an authorized repair facility for service.
No intake air preheater is installed, and it is too cold to start without one.	Install an intake air preheater.
The intake air preheater is malfunctioning.	Check the intake air preheater, and replace it, if necessary.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are out of adjustment.	Push both sensors into their holes as far as they will go. If this does not solve the problem, bring the vehicle to an authorized repair facility for service.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are damaged.	Bring the vehicle to an authorized repair facility for service.
There is air in the fuel system.	Check the fuel lines for air pockets. Prime the fuel system and start the engine.
The air filter is clogged.	Clean or replace the air filter.
The fuel filter is clogged.	Replace the filter element.
The exhaust brake valve is malfunctioning.	Have an authorized repair facility check the operation of the valve.
The valves are not adjusted properly.	Check the valve lash.
There are other problems in the fuel system.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Starts Only After Cranking for a Long Time
Cause	Remedy
The fuel tank is low or empty.	Add fuel and prime the fuel system, if necessary.
There are leaks in the fuel lines.	Check the fuel lines for leaks and repair them, if necessary.
The fuel filter is clogged.	Replace the filter element.
The fuel line, the fuel prefilter, or the screen in the fuel tank is blocked.	Clean and prime the system. Have the fuel lines and filters checked by an authorized repair facility.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are out of adjustment.	Push both sensors into their holes as far as they will go. If this does not solve the problem, bring the vehicle to an authorized repair facility for service.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are damaged.	Bring the vehicle to an authorized repair facility for service.
There are other problems in the fuel system.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Starts, But Dies
Cause	Remedy
The fuel tank is low or empty.	Add fuel and prime the fuel system, if necessary.
The fuel filter is clogged.	Replace the filter element.
The fuel line, the fuel prefilter, or the screen in the fuel tank is blocked.	Clean and prime the system. Have the fuel lines and filters checked by an authorized repair facility.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are out of adjustment.	Push both sensors into their holes as far as they will go. If this does not solve the problem, bring the vehicle to an authorized repair facility for service.
The camshaft position (CMP) sensor and/or the crankshaft position (CKP ) sensor are damaged.	Bring the vehicle to an authorized repair facility for service.
The constant-throttle valves are malfunctioning.	Bring the vehicle to an authorized repair facility for service.
There are other problems in the fuel system.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Fan Doesn't Work
Cause	Remedy
The fan hub is damaged.	Replace the fan hub.
The fan wiring is damaged.	Repair the fan wiring.
The parameter settings in the MCM or Common Powertrain Controller (CPC) are incorrect.	Have an authorized repair facility reprogram the control unit.

Problem—The Engine Fan Is Constantly On
Cause	Remedy
The fan override switch is on.	Check the operation of the fan override switch.
The fan hub is damaged.	Replace the fan hub
The parameter settings in the MCM or CPC are incorrect.	Have an authorized repair facility reprogram the control unit.
AC switch is damaged	Check AC switch.

Problem—Fuel Consumption Is Too High
Cause	Remedy
The tires are not properly inflated.	Check all tires for correct pressure.
The air filter and/or intake air system is clogged.	Check the air restriction indicator. Clean the intake air system and replace the air filter if necessary.
The exhaust brake valve is malfunctioning.	Have an authorized repair facility check the operation of the valve.

Problem—The Engine Performs Poorly, Does Not Develop Full Power
Cause	Remedy
The air filter and/or intake air system is clogged.	Check the air restriction indicator. Clean the intake air system and replace the air filter if necessary.
The exhaust brake valve is malfunctioning.	Have an authorized repair facility check the operation of the valve.
The fuel filter is clogged.	Replace the filter element.
There are other problems with the fuel system.	Bring the vehicle to an authorized repair facility for service.
The valves are not adjusted properly	Check the valve lash.
The coolant temperature sensor is damaged or reading incorrectly.	Bring the vehicle to an authorized repair facility for service.
The fuel temperature sensor is damaged or reading incorrectly.	Bring the vehicle to an authorized repair facility for service.
The engine oil temperature sensor is damaged or reading incorrectly.	Bring the vehicle to an authorized repair facility for service.
The charge-air temperature sensor is damaged or reading incorrectly.	Bring the vehicle to an authorized repair facility for service.
There are problems with the MCM or CPC.	Bring the vehicle to an authorized repair facility for service.
There is internal damage to the engine.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Is in Emergency Running Mode (constant speed 1,300 rpm)
Cause	Remedy
The MCM or CPC is damaged.	Bring the vehicle to an authorized repair facility for service.
An incorrect parameter is in the MCM or CPC.	Bring the vehicle to an authorized repair facility and have the parameter settings reprogrammed in the MCM or CPC.

Problem—The Coolant Temperature Is Above Normal
Cause	Remedy
The coolant level is too low.	Check for coolant leaks, and repair as needed.
The poly-V belt is loose.	Tighten or replace the poly-V belt.
The coolant temperature gauge and/or sensor is not reading correctly.	Bring the vehicle to an authorized repair facility for service.
The radiator is damaged or dirty.	Clean the radiator. Repair or replace the radiator if necessary.
The water pump is damaged.	Have an authorized repair facility replace the water pump.
The thermostat is damaged.	Have an authorized repair facility replace the water pump.
The fan is not operating properly.	Bring the vehicle to an authorized repair facility and have the fan hub checked or have the parameter settings reprogrammed in the MCM or CPC.

Problem—The Coolant Temperature Is Below Normal
Cause	Remedy
The coolant temperature gauge and/or sensor is not reading correctly.	Bring the vehicle to an authorized repair facility for service.
The thermostat is not operating properly.	Have an authorized repair facility replace the thermostat.
The fan is not operating properly.	Bring the vehicle to an authorized repair facility and have the fan hub checked. Bring the vehicle to an authorized repair facility and have the parameter settings reprogrammed in the MCM or CPC.

Problem—The Cooling System Is Losing Coolant
Cause	Remedy
There is an external coolant leak.	Repair the leaking component.
The radiator cap is leaking.	Replace the radiator cap.
The air compressor head is damaged.	Have an authorized repair facility replace the air compressor.
The cylinder head gasket is leaking.	Have an authorized repair facility replace the head gasket.

Problem—There Is Coolant in the Engine Oil
Cause	Remedy
The cylinder head gasket is damaged.	Have an authorized repair facility replace the head gasket.
The oil/water heat exchanger is leaking.	Have an authorized repair facility replace the heat exchanger.
There is an internal coolant leak.	Bring the vehicle to an authorized repair facility for service.

Problem—There Is Foam in the Engine Oil
Cause	Remedy
The oil level is too low or too high.	Correct the oil level.
The oil has not been changed within the recommended interval.	Change the oil.
The oil is not of the recommended quality.	Change the oil.

Problem—The Engine Oil Pressure Is Low
Cause	Remedy
The oil pressure gauge and/or sensor is not reading correctly.	Bring the vehicle to an authorized repair facility for service.
There is fuel in the oil.	Bring the vehicle to an authorized repair facility for service.
The oil filter is clogged.	Replace the filter element.
The oil filter bypass valve is damaged.	Replace the bypass valve.
The oil pump and/or relief valve is damaged.	Have an authorized repair facility replace the oil pump.

Problem—The Engine Exhaust Is White
Cause	Remedy
The fuel is of poor quality.	Add fuel of the right quality.
The intake air preheater is malfunctioning.	Check the intake air preheater, and replace it, if necessary.
The valves are not adjusted properly.	Check the valve lash.

Problem—The Engine Exhaust Is Black
Cause	Remedy
The air filter and/or intake air system is clogged.	Check the air restriction indicator. Clean the intake air system and replace the air filter if necessary.
The exhaust brake valve is malfunctioning.	Have an authorized repair facility check the operation of the valve.
The intake air preheater is malfunctioning.	Check that the heater is not staying on all of the time.
The valves are not adjusted properly.	Check the valve lash.
There is damage to the fuel system: the fuel pump, one or more fuel injectors, or one or more unit pumps are damaged.	Bring the vehicle to an authorized repair facility for service.
The charge-air temperature sensor is damaged.	Bring the vehicle to an authorized repair facility for service.
There is internal damage to the engine.	Bring the vehicle to an authorized repair facility for service.

Problem—The Engine Exhaust Is Blue
Cause	Remedy
The engine oil level is too high (engine oil is reaching the combustion chamber).	Adjust the oil level, and then have the oil level checked by an authorized repair facility.
The turbocharger is leaking oil.	Have an authorized repair facility replace the turbocharger
The valve stem seals are loose or damaged.	Have an authorized repair facility replace the seals.
The piston rings are worn.	Have an authorized repair facility replace the piston rings.

Problem—Engine Brake Performance Is Poor
Cause	Remedy
The engine brake control switch is damaged.	Replace the switch
The exhaust brake is not operating properly.	Have an authorized repair facility check the operation of the valve.
The constant-throttle valves are malfunctioning.	Bring the vehicle to an authorized repair facility for service.
Components of the MCM and/or CPC are damaged.	Bring the vehicle to an authorized repair facility for service.

Problem—Cruise Control Is Not Working
Cause	Remedy
One or more of the cruise control switches are damaged.	Replace the damaged switch.
Components of the MCM and/or CPC are damaged or not working properly.	Bring the vehicle to an authorized repair facility for service.

Problem—The Battery Charge Indicator Light Does Not Come On When the Engine Is Not Running
Cause	Remedy
The bulb is bad.	Replace the bulb.
The circuit is broken.	Repair the break in the circuit.

Problem—The Battery Charge Indicator Light Comes On When the Engine is Running
Cause	Remedy
The poly-V belt is too loose.	Check the belt tension; if necessary, Have an authorized repair facility replace the belt tensioner.
The belt tensioner is damaged.	Have an authorized repair facility replace the belt tensioner.
The poly-V belt is worn or damaged.	Replace the belt.
The alternator is damaged (has a damaged rectifier or voltage regulator).	Have an authorized repair facility replace the alternator.