Category Archives: Fault Codes

Fault code based troubleshooting

Fault Codes 3720/15 & 3720/16

Published / by Mechanic / 1 Comment on Fault Codes 3720/15 & 3720/16

Both codes indicate that the DPF has reached the end of its service life and must be replaced.  Replace DPF and perform Ash Accumulator reset using DDDL.

Aftertreatment maintenance intervals:

  • EPA 07: Remove ash at 300,000miles(480,00km) or 9,000 hours
  • EPA10/GHG14: Remove ash at 300,000-400,000miles(480,000-640,000km) or 9,000-10,250 hours
  • EPA10/GHG14: DEF pump filters are to be replaced every 150,000miles(240,000km)
  • EPA10: DEF pump air bladder, needs to be refilled every 24 months

3251/0 EPA10 DPF pressure out of range, very high

Published / by Mechanic / 4 Comments on 3251/0 EPA10 DPF pressure out of range, very high


This Fault Code Sets when the Diesel Oxidations Catalyst (DOC) Inlet Pressure is 35 kPa (5 psi) Greater Than the Diesel Particulate Filter (DPF) Outlet Pressure for more than 10 Seconds.

The ACM monitors the DOC inlet pressure sensor & DPF outlet pressure sensor. This will cause a 25% derate/power loss.


  1. Check for other fault codes, if codes 3609/3 or 3609/4 are present. Diagnose those codes first.
  2. Using DDDL go to service routines> SCR & DPF voltages
  • Monitor DOC inlet pressure sensor voltage pin 87. If voltage is NOT between 0.44-0.56 volts replace the DOC inlet pressure sensor.
  • Monitor DPF outlet pressure sensor voltage pin 72. If voltage is NOT between 0.44-0.56 volts replace DPF outlet pressure sensor.

3. If all sensors check out okay, perform a Low temp by disconnecting DEF metering unit connector then navigating to the Service routines>DFP then perform a low temp regen. Then monitor DOC inlet temp & DPF outlet temp sensor readings:

    • If the DOC oullet temp sensor reading follows the DOC inlet temp sensor reading, replace the failed DPF. Regen to verify the repair
    • If the DOC outlet temp sensor reading does NOT follow the DOC inlet temp sensor reading, replace the failed DOC. Regen to verify the repair.

1077/14 Internal/External Leakage of the High Pressure Fuel System

Published / by Mechanic / 4 Comments on 1077/14 Internal/External Leakage of the High Pressure Fuel System


This code indicates high leakage in the high pressure fuel system(fuel rail pressure). This light will indicate both the MIL and CEL but with no engine reactions, no de-rate and engine shutdown. This is for a 3 filter fuel system EPA 07/10.


  1. Check for other fault codes. If 1077/14 is present, you must troubleshoot that fault code first as it will trigger this fault code as well.
  2. Perform an automated fuel system integriy check (FSIC) using DDDL.
  • If longer then 35 seconds, perform the same test while road testing the unit. If the Fault code does not come back again, release the unit or obtain driver info of specific situation¬† fault occurs.
  • If less then 35 seconds, check for internal & external fuel leaks. Repair any faults/damages.
  1. If no leaks are present, perform an Idle speed balance test. Compare values.
  • If any cylinders are above 70% or below -70% remove each Fuel Injector transfer tube one at a time. Install cap tool J-48704 and perform a FSIC test. If the bleed off time is longer then 35 seconds replace the cylinders injectors
  • If no cylinder is above 70% or below -70% then inspect the PLV for leaks, and replace if leaking.

How to check High Pressure fuel system for leaks:

  1. Inspect high pressure pump fuel lines for kinks/damage or loose fittings, Repair as necessary.
  2. Inspect fuel injector tubes and connections at the fuel rail for kinks/damage or loose fittings. Repair as necessary.
  3. Inspect the fuel rail pressure sensor. Replace if leaking or loose.
  4. Inspect the fuel pump for external leaks (typically at the flanges). Replace if leaking.
  5. Cap all six injectors using tool J-48704, then attempt to start the engine. Using DDDL monitor rail pressure.
  • If rail pressure reaches desired rail pressure, then check rail pressure bleed down. If rail pressure bleeds down a 100 bar in less then five minutes then replace the high pressure fuel pump.
  • If rail pressure does not reach desired rail pressure, then replace the high pressure fuel pump.

PLV leakage checks:

  • Install clear hose to the PLV return line. Cap PLV return line on the fuel filter module. Perform a FSIC test. Any flow out the PLV indicates internal leakage. Replace the PLV and reset the PLV counter to 0.


Selective Catalyst Reduction NOx Conversion Very low 4361/1 & 4364/18

Published / by Mechanic / 9 Comments on Selective Catalyst Reduction NOx Conversion Very low 4361/1 & 4364/18

One of the most common fault codes occurring in EPA10/GHG14 model units. This fault code appears when the ACM reads that NOx conversion is lower then spec. Based off the SCR inlet & outlet NOx sensors.

Conditions in which the code will appear:

  • During regen the DEF doser begins dosing
  • 1000-1500 rpm @15-100% load
  • SCR inlet temp less then 650C/ambient temp greater than 0C/coolant temp greater than 70C

This code will put the unit in a derate for at least one drive cycle but will not shut down the unit.

How to troubleshoot

  1. Verify no other emission related components were recently repaired. Perform a regen to verify code.
  2. Verify for any air system related fault codes, if any repair those first.
  3. Verify for any EGR related faults, if any repair those first.
  4. Verify for any DEF related faults, if any repair those first.
  5. Verify for any NOx sensor, DPF/DOC/SCR temp or pressure sensor fault. If any repair those first.
  6. Check DEF quality, verify there is no contamination. Use P/N DDE W060589001900 for more accurate readings. Replace DEF and flush system if any damage/contamination is present, then regen to verify repair.
  7. Using DDDL compare DEF pressure sensor to barometric pressure sensor reading. Make sure they are within 4.3PSI, if not replace DEF pressure sensor.
  8. Using DDDL perform DEF quantity test. Remove the DEF doser injector and verify the quantity of DEF fluid being sprayed. Spec is between 100-135ml. If not replace and regen to verify repair.
  9. Disconnect DEF doser injector connector and perform a Low temp regen using DDDL. Monitor inlet & outlet NOx sensor readings(PPM) make sure they are within 50ppm, if not replace the sensor with most inaccurate/erratic reading.
  10. After all basic checks have been performed. Regen the unit and monitor NOx efficiency and release unit if unit has over 70% efficiency.
  11. If unit does not pass a regen perform another regen and monitor SCR inlet & outlet temp sensors.
  • If the inlet SCR temp sensor reads 38C lower than the SCR outlet temp sensor, replace the One box and check for up stream failure
  • If temp sensors are within 38C, perform another low Temp regen. Monitor DPF/SCR temp sensors and replace sensors that have an erratic movement during the regen process.