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2003-2007 Cummins 5.9L Diagnostics

High Pressure Common Rail Basic Information
 The high pressure pump builds the high pressure and delivers it to the fuel rail manifold where it flows through the injector lines and injector connector tubes to the injectors. The fuel pressure regulator (fuel control actuator) in the high pressure pump controls fuel rail pressure. The injectors have a hollow check ball that holds high pressure fuel until the fuel solenoid is actuated by the ECM, this allows the check ball to rise off its’ seat and an injection to take place. If the injector connector tubes, where they seat into the injectors, leak or the check ball in the injector is leaking or the high pressure limit valve then it will not build enough rail pressure to start the engine. It takes approximately 4000 PSI rail pressure to start the engine.
dodge cummins diesel common rail injector cutaway

 The fuel system contains high pressure fuel up to 25,000 PSI. Do Not use you fingers to find fuel leaks! High pressure fuel entering your bloodstream may result in amputation or loss of life.

Preliminary checks

  1. Record and repair any active DTC, they may be related to complaint
  2. Ensure that you have a good clean fuel supply and good fuel supply pressure.

No Start or Hard Start

  1. No or low fuel supply to the high pressure pump (CP3)
  2. Monitor rail pressure and see if you have over 4000 PSI during cranking, if not one or more injectors can cause a hard start, see injector section for further diagnostics. No smoke from the tailpipe after about 10 seconds of cranking means no fuel is getting into the cylinders.
  3. Injector connector tube not seated in injector, bad tube or improper torque on nut.
  4. Leaking fuel pressure limit valve, should not leak at idle or during cranking.
  5. Verify high pressure pump output volume (see high pressure pump info). You can also cap off all the injectors and see how quickly the rail pressure climbs. It takes about 4000 PSI rail pressure in order to start.
  6. Shorted fan clutch, unplug fan and try starting again.

Black Smoke

  1. If at idle, use the scan tool to cut out one cylinder at a time and see if the smoke disappears.
  2. Dirty air filter
  3. Exhaust leaks or Boost leaks, you can usually hear a boost leak as a high pitched squeal under load.


  1. Use scan tool to isolate one cylinder at a time.
  2. A bad or incorrect torque on an injector connector tube, missing or damaged chamber gasket, low compression or excessive valve lash could all cause a miss.


  1. Use scan tool to isolate one cylinder at a time
  2. Use cap off tool 9011 to block off one injector at a time.

Surge at idle

  1. Low or no fuel supply pump pressure to the high pressure pump
  2. Actual pressure versus desired pressure too far apart, map the fuel pressure graph, may be a bad FCA (fuel control actuator). If you have a fluctuation over 500 PSI this can cause a surge.

White - Blue smoke at idle when cold
  If the smoke clears in less than 1 minute, this would be normal depending on temperature and altitude. Blue white smoke that burns your eyes, is un-burnt fuel, cold temperatures, high altitude and excessive idle time all mean cold

  1. Possible bad injector, leaking at the nozzle tip. Use the scan tool to kill one injector at a time to isolate. However, this does not reduce rail pressure in the injector and the tip can still leak fuel. Cap off the rail one line at a time (cap is tool # 9011) to pinpoint injector.  
  2. The intake air temperature, engine coolant temperature, inlet air temperature and battery temperature should all display normal ambient temperatures when cold. If not, repair as necessary.
  3. Check intake heater operation when cold.
  4. Check rail pressure when engine is off, it should be 0 PSI (+/- 500 PSI).
  5. Low or no fuel supply pressure, supply pump or fuel filter etc.
  6. Excessive idle time can cause white smoke when cold due to carbon build up on       injector tips. More than 20% idle time is excessive.


  1. Upper injector o-ring
  2. Cracked injector, remove valve cover and inspect for leaks while the engine is running. A leak will often look like a fog or haze of fuel.
  3. Leak at the high pressure pump driveshaft seal.

Fuel Supply Pump

  • 2003 and 2004 model years originally had the fuel supply pump mounted on the fuel filter housing. 2005 through 2007 5.9L had the fuel supply pump mounted in the tank. There are replacement fuel supply pumps for 2003 and 2004 that mount on the fuel filter housing, but have been updated to a different style. There are also fuel supply pumps that mount on the frame rail and replace the in tank supply pumps, such as the FASS pump and the BD Max-Flow pump. Test the fuel supply pressure at the inlet to the CP3 pump. Normal pressure is 10 PSI at idle and they typically drop close to zero PSI under load. Zero supply pump pressure will not damage the CP3 high pressure pump like it does to the earlier VP44 pump
  • High Pressure Pump (CP3 Pump)

    1. Most starting problems due to low pressure are caused by bad (check ball seat) injectors. You can unplug the fuel control actuator and the pressure should default to maximum pressure (23,500 PSI), however if there is a leak in the high pressure system then the pump will not build enough pressure.  If there has been a major contamination issue with dirt and or water then it is very likely that the high pressure pump will need to be replaced. The injectors are typically damaged first, but any contamination that got into the injectors also went through the CP3 pump.
    2. Volume test; the CP3 pump should discharge 70 ml (at 150 rpm or 90 ml at 200 rpm), from the CP3 to rail manifold fuel line, in 3 10 second cranking intervals (total of 30 seconds cranking). Remove the fuel discharge line from the CP3 pump to test out put.
    3. If the cascade over flow valve is bad this can send fuel out the return line instead of to the charging circuit of the CP3 pump.

     It takes about 4000 PSI rail pressure in order for the injectors to deliver fuel and the engine to start.

    1. Maximum allowable leakage for all injectors combined is 160 ml per  minute: check when engine coolant temperature is above 180 degrees, 1200 rpm and fuel rail pressure is equal to 20,305 PSI.  
    2. Any injector contributing more than 40 ml is excessive. IE: if total leakage is 200 ml and blocking off number one injector reduces the total leakage to 160 ml, cylinder number one injector has excessive leakage and is bad.
    3. If you have a no start condition, maximum allowable return is 90 ml per minute at 200 rpm cranking speed, be careful not to over heat the starter during testing.
    4. Damaged or loose high pressure injector connectors can cause excessive leakage.
    5. Excessive leakage usually results in a starting issue, which could occur hot or cold, but usually occurs hot because the fuel is thinner when hot.

    Use the following information regarding diagnostic trouble codes in addition to the normal diagnostic procedures outlined in the service manual or technical service bulletins.

    DTC P0148; high pressure common rail checksum, which is a deviation between the fuel pressure set point and the actual fuel pressure.

    1. FCA, check for rust on the fuel control actuator, which could indicate other fuel system problems caused by water contamination.
    2. Fuel pressure sensor
    3. Lift pump or fuel supply issues, check fuel supply pressure and fuel filter condition.
    4. Cascade over flow valve
    5. Pressure limit valve
    6. Injectors, excessive return, see injectors
    7. High pressure pump (CP3)

    DTC P0300 – P0306; injector misfire, all and 1 through 6

    1. Low fuel supply pressure
    2. Use scan tool to isolate each cylinder

    DTC P0217; decreased engine performance due to a engine overheat condition

    1. Check ECT sensor
    2. Restricted air flow (caked dirt and bugs) through the intercooler and radiator.

    DTC P0251; CP3 pump regulator control, ECM detects a discrepancy between PWM signal supplied to FCA and the PWM returned from FCA

    1. Low or no fuel supply pressure (bad supply pump or plugged filter)
    2. Fuel Control Actuator (FCA) bad, use the scan tool to verify rail pressure set point versus fuel pressure. Normal idle pressure is 6000 – 7000 PSI. If you have a fluctuation over 500 PSI this can cause a surge as well.

    DTC P0336; crank position sensor (CKP) signal, CLP below calibrated value

    1. Excessive cranking with a no start condition
    2. CKP sensor
    3. CKP wiring issue
    1998-2002 Cummins 5.9L 24 Valve Diagnostics

    The fuel supply pump pressure is critical for the longevity of the VP44 injection pump. The fuel supply pump should maintain at least 4psi at the inlet to the injection pump on a W.O.T. test drive. Failure to maintain a pressurized flow of un-aerated fuel will cause injection pump damage.
    4psi at the inlet to the injection pump with a clean fuel filter allows for a pressure drop across the fuel filter when it is dirty. According to Chrysler, pressure doesn't matter, only volume. The problem with their volume test with an unrestricted flow is their specifications for volume aren't high enough. Some vehicles with the updated in-tank supply pump won't maintain a positive pressure during a test drive. When the supply pump in the injection pump is pulling more fuel than the supply pump in the tank is pushing, then pressure becomes a vacuum because volume isn't high enough. Continued driving, when fuel is under a vacuum, can cause cavitations, which will damage the injection pump.

    In order to maintain good fuel flow, especially with performance modifications, you may need to add an additional supply pump.

    NOTE: The following information is not a substitute for the proper diagnostic manuals, but to share some of the common problems we have run across.

    Performance boxes that tap into, or connect into, vehicle wiring should be removed to make certain that they are not causing any of the following complaints.

    "Normal" life seems to be about 150,000 miles. When injectors are going bad, they can cause many different intermittent problems, such as: no start, hard start, black smoke, low power, white smoke and rough running.

    1. Low or no fuel supply pressure.
    2. Dirty air filter or inlet restriction.
    3. Exhaust leak before the turbo.
    4. MAP sensor can go bad and not set a code, check reading with scan tool versus actual.
    5. Injectors bad

    1. Low or no supply pressure.
    2. No fuel - sending unit in tank defective.
    3. If the supply pump recently failed, it could damage the injection pump and cause a no start.
    4. Check for DTC, follow Powertrain Diagnostic Procedures Manual.

    1. Check injectors, remove injection lines and crank engine. Do any of the injector feed tubes pump compression back out while cranking? Replace injector, if needed.
    2. CMP sensor defective.
    3. Injection pump

    1. Follow the same guidelines as no start.
    2. Fuel leaks at injector feed tubes, internal or external?
    3. If supply pump recently failed, it could cause injection pump problems due to cavitation damage.

    1. Check for DTC.
    2. Check injectors.
    3. Leaking fuel injector tubes may also cause a miss. If they leak externally, they are also leaking at the injector connection.

    1. No or low fuel supply pump pressure.
    2. 98 & early 99 automatic transmission, see TSB on erratic torque converter clutch operation - needs reflash

    1. No or low fuel supply pressure.
    2. DTC present? Look at solving the codes first.
    3. With black smoke and no DTC, possible bad injectors.

    In addition to the information in the Diagnostic Procedure Manuals, consider the following checks and information.

    DTC 215 - Fuel Injection Pump Control Circuit
    1. Swap injection pump relay with horn relay and retest.

    DTC 216 - Fuel Injection Pump Timing Failure
    1. If supply pump previously failed (within the last 2-3 months) it could cause advance component and housing damage in the injection pump.
    2. Low or no fuel supply pump pressure.
    3. Improper installation of replacement injection pump. Key not aligned with gear and gear pulled onto shaft with driveshaft nut.
    4. Injection pump drive gear installed one tooth off.

    DTC230 - Transfer Pump Circuit Out of Range
    1. Bad fuel Supply pump will normally cause this code.
    2. Could also cause a DTC216.
    3. Could set due to excessive cranking, see hard start diagnostics.

    DTC336 - Engine Crankshaft Position Sensor (CKP) Signal
    1. Indicates no engine speed or position signal to ECM.
    2. Can cause other codes, solve DTC336 first.
    3. Reads out on scan tool as ECM engine speed.
    4. Will cause multiple problems, such as surge, miss erratic run, hard start, no start, stalls, etc.

    DTC370 - Fuel Injection Pump Speed / Position Sensor Signal Lost
    1. If no other DTC, pump is likely faulty.

    DTC602 - ECM Fueling Calibration
    1. Could be caused by a performance box.
    2. Can also be caused by a DTC336.

    DTC1688 - Internal Fuel Injection Pump Failure
    1. This code can be caused by a bad crank sensor (DTC336)
    2. If no other DTC, most likely injection pump needs to be replaced due to an electronic failure.

    DTC1689 - No Communication Between ECM and Injection Pump Module
    1. Can be caused due to excessive cranking - See hard start & no start diagnostics.
    2. Wires chaffed at pump connection.
    3. Performance box problem.
    4. Fuel pump relay bad (swap with horn relay and retest).
    5. Possible defective pump.

    DTC1690 - Fuel Injection Pump CKP Sensor Does Not Agree With ECM CKP
    1. Monitor RPM reading of the following: ECM engine speed (crank position sensor See DTC336) vs. engine speed CMP (cam position sensor) vs. injection pump engine RPM (from injection pump).
    2. Can be caused by a DTC336 - repair DTC336 FIRST

    DTC1691 - Fuel Injection Pump Controller Calibration Error (PSG)
    Likely an injection pump problem.

    DTC1693 - DTC Detected in PCM
    The JTEC controller is reporting that there is a DTC stored in the PCM.

    1994-1998 Cummins 5.9L 12 Valve Dianostics

    Hard start, no start

    1. Check that the shutoff solenoid is working and getting full travel.

    Low Power

    1. Low fuel galley pressure. (see Overflow valve/supply pump)
    2. Dirty fuel filter.
    3. Restricted air intake, dirty air filter.
    4. Check throttle for full travel at injection pump.
    5. Check to see that the shut off solenoid is pulling completely into the run position.
    6. Check for exhaust manifold leaks, exhaust leaks won't let the turbo spool up and create full boost.
    7. Check the intercooler hose connections; these can often slip off the intercooler piping especially in high boost situations.
    8. Loose or cracked boost line leading to AFC (aneroid) hosing in injection pump.
    9. Damage AFC diaphragm, check to see if it will hold a vacuum.

    Miss, Blue/White Smoke

    1. Low fuel galley pressure (see Overflow valve and Fuel Supply Pump)
    2. Air in fuel system to injection pump.
    3. Pump to engine timing is retarded. If you have checked the fuel galley pressure and it is good, then you can try the following; after the vehicle sits overnight start the engine and as soon as the oil pressure gauge starts to move increase the engine to 1800 rpm. If the white smoke and miss are cleared up in less than 7 seconds, then the pump to engine timing is usually good. If it takes longer than 7 seconds to clear up the smoke and rough run you may need to check the pump to engine timing.
    4. Bad injector or pump problem.
    5. If you have changed the injection pump, and it ran fine for a shot time then starts missing, smoking or dies with no restart then the pump camshaft nut was not torqued correctly.

    Stalling or dies on deceleration

    1. Idle speed too low, idle speed should be 800-850 rpm.
    2. If you have a start and die or a long crank time after the vehicle sits overnight then you may need to replace the return line off of the injection pump. The 5/16" rubber hose connects to the steel line on the back of the injection pump and is located behind the fuel filter housing. If the line is cracked or "checked" on the outside it will allow fuel to drain back overnight. Make sure to put a slight "camel hump" in the line to prevent fuel drain back (cutting the line too long will make it "hump" upward).


    Air Intake Heater

    1. The engine will start cold down to about 35 degrees without the intake heater working. The PCM gets a signal from the intake air temperature sensor and activates the heater via the air intake heater relays, if the air intake temperature is below 60 degrees. The heater will continue to cycle after the engine is started for a short time.
    2. The colder it is and the higher in elevation you are the more you need the intake heater for faster cold starting and reduced smoke.
    3. You can watch the volt gauge to see if the intake heater is cycling; it will drop to about 10 volts while the engine is running.



    1. Loosen each injector line one at a time and note which line does not make a difference on how it runs.
    2. When diagnosing a miss you can move the possible bad injector to a different hole and see if the miss follows it. If not then you are looking at a possible pump or engine problem on that cylinder.
    3. We do not see many injector problems on the 94-98 12 valve engines, they are usually good for 200k miles or more.


    Injection Pump

    1. Pump to engine timing is critical to the engines performance. If the timing is retarded then you will have a low power and often a blue/white smoke complaint (worse cold).
    2. If you have white smoke and a miss when cold check the fuel galley pressure first. If the galley pressure is good (see overflow valve and supply pump) try the following on a cold start. Start the engine cold, as soon as oil pressure registers on the gauge increase the engine rpm to 1800. The engine will smoke and miss, if the smoke and miss doesn't clear within 7 seconds the pump to engine timing may need to be reset.
    3. Pump drive nut torque; clean gear and camshaft before installing, pre-torque to 10 ft. lbs, unlock the timing pins on the engine and injection pump. Final torque 165 ft. lbs (some manuals show 125 ft lbs...this is WRONG). Incorrect torque will allow the drive gear to slip resulting in white smoke or dies with no restart shortly after installation.


    Overflow Valve and Supply pump

    1. Fuel galley pressure (check at inlet to injection pump) should be 20psi at idle and a minimum of 25psi at 2500rpm. If it is low, the most common problem is the overflow valve, but a weak fuel supply pump can also cause the same problem, as well as restricted fuel supply.
    2. Change the fuel filter.
    3. Use pliers with a soft jaw and temporarily pinch the return hose off of the injection pump. The supply pressure should spike very quickly to 50 psi. If the pressure goes to 50 psi or above the overflow valve will need to be replaced. If not then you have a bad supply pump, restricted fuel supply (fuel heater screen or tank sock) or the fuel heater is sucking air.


    Shut off solenoid

    1. The shut down solenoid is controlled by two relays one for pull-in during cranking (70 amps) and one for hold-in during running. If the shut off solenoid does not pull up be sure to check the relay and replace if needed prior to replacing the shut off solenoid.
    2. Look in your service manual for the wiring diagram.



      • The turbocharger is “powered” by exhaust gas velocity (expanding exhaust gases). Revving the engine up while in neutral will produce low boost. To accurately measure boost pressure you must have the engine under load, such as full throttle acceleration while driving.
      • If you are lacking fuel (galley pressure) at the right time (timing) or have an exhaust leak (loss of exhaust gas velocity) the turbo will not produce the correct boost. Solve these problems first, before replacing the turbocharger.
      • The turbo should spin freely while pushing the turbine shaft left, right, up and down while gently rotating the compressor wheel. The compressor wheel should turn freely by hand, if it doesn't replace the turbocharger.
      • Visually inspect the compressor wheel. The blades should not contact the compressor housing and the blades should not be chipped, bent or damaged in any way.
      • Check the wastegate actuator for free movement while applying regulated air pressure, the wastegate should start moving open with about 20 psi applied to it (check the specifications for the turbo you are checking).

    1989-1993 Cummins 5.9L Diagnostics

    Cold Advance Operation; The KSB unit on the injection pump uses a temperature sensor in the intake manifold to advance the pump to engine timing when the engine is cold, which reduces blue/white smoke.

    1. 89 to early 91 used a wax motor style KSB unit that voltage is applied to, via the cold start switch, once the intake air temperature is above 160 degrees.
    2. 91.5 to 93 used a solenoid style KSB. The intake air temperature sensor applies 12 volts to the KSB solenoid until intake air temperature is above 90 degrees.

    Low Power

    1. Check for full throttle travel, worn levers or throttle spring on the injection pump can limit travel.
    2. Pump to engine timing off
    3. Bad AFC diaphragm, check to see if it will hold a vacuum
    4. Exhaust manifold leak (low turbocharger boost)


    Slow to shut off

    1. Remove the overflow valve and tap out onto a sheet of white paper, or remove the shutoff solenoid. If there are a lot of metal particles, the injection pump is coming apart inside (we see this happen frequently after approximately 150,000 miles) and must be changed along with the injectors (the metal will have been pumped through the injectors).


    Miss/Rough run

    1. As above, if the pump has a lot of metal in it, the metal can plug some of the spray holes in the nozzle tip. If there are holes plugged in the nozzles, find and fix the cause before replacing them (if the problem is in the pump, the replacement nozzles will soon plug as well).
    2. If during cold start, see cold start operation
    3. Pump to engine timing incorrect.
    4. Idle speed too low, should be 700-800 rpm


    Smoke, Blue/White

    1. Blue/White smoke, if during cold start, see cold start operation.
    2. Check intake air heater operation.
    3. Dirty fuel filter
    4. Low fuel supply pressure


    Smoke, Black

    1. Dirty or restricted air filter


    Supply Pump

    1. 1. Supply pump pressure should be about 4-5 PSI at idle



    1. The turbocharger is powered by exhaust gas velocity (expanding exhaust gases). Revving the engine up while in neutral will produce low boost. To accurately measure boost pressure you must have the engine under load, such as full throttle acceleration while driving.
    2. if you are lacking fuel (galley pressure) at the right time (timing) or have an exhaust leak (loss of exhaust gas velocity) the turbo will not produce the correct boost. Solve these problems first, before replacing the turbocharger.
    3. The turbo should spin freely while pushing the turbine shaft left, right, up and down while gently rotating the compressor wheel. The compressor wheel should turn freely by hand, if it doesn't replace the turbocharger.
    4. Visually inspect the compressor wheel. The blades should not contact the compressor housing and the blades should not be chipped, bent or damaged in any way.