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SPN 4334/FMI 7 - EPA10
DEF Pressure Low
This code sets when the Aftertreatment Control Module (ACM) detects that the Diesel Exhaust Fluid (DEF) pump is not building 72 psi during a pressure build cycle (60 seconds).
SPN 4334/FMI 7
DescriptionDEF Pressure Low
Monitored ParameterDEF Pressure
Typical Enabling ConditionsPressure Limiting Unit On, Dosing Enabled
Execution FrequencyContinuous when enabling conditions met
Typical Duration60 Seconds
Dash LampsMIL, CEL
Engine ReactionDerate 25%
VerificationSCR Quantity Test
NOTE: If there is oil present in the air system, the Pressure Limiting Unit (PLU), Diesel Exhaust Fluid (DEF) metering unit and the associated air lines should be cleaned to prevent repeat failures.
To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area. Engine exhaust is toxic.
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.
To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 276 kPa (40 psi) air pressure.
NOTE: It is normal to have some DEF discharge from the pump outlet after the SCR air pressure test has been performed.
- Check the DEF for contamination. Refer to section "Checking Diesel Exhaust Fluid Quality" . Is there contamination in the DEF?
- Yes; Refer to section "Diesel Exhaust Fluid in Fuel" for fuel intrusion or Refer to section "Diesel Exhaust Fluid in Coolant" for coolant intrusion. Verify repair.
- No; Go to step 2.
- Connect DiagnosticLink® . Go to step 3.
- Turn the ignition ON (key ON, engine OFF). Go to step 4.
- Check for other fault codes. Are there any fault codes present for the following components?
- Pressure Limiting Unit (PLU)
- DEF pump
- DEF pressure sensor
- DEF air pressure sensor
- DEF tank level/zone faults
- Low DEF air pressure
- Yes; diagnose and repair the other fault codes first. Verify repair.
- No; Go to step 5.
- Start and run the engine to build up the air pressure in the vehicle. Does the air pressure in the secondary air system build and hold above 689 kPa (100 psi)?
- Yes; Go to step 6.
- No; Refer to section "Will Not Build Air Pressure or Slow to Build Air Pressure" .
- Turn the ignition OFF. Go to step 7.
- Wait five minutes for the purge cycle to complete. Go to step 8.
- Visually/audibly inspect air supply lines for leaks, kinks, cracks or melting from the air tank to Pressure Limiting Unit (PLU) and from pressure limiting unit to DEF pump and DEF metering unit. Are there any damaged lines or air leaks present?
- Yes; repair as necessary. Verify repair.
- No; Go to step 9.
- Disconnect the air supply line at the DEF pump (1). Go to step 10.
- Connect a suitable air pressure gauge (0 to 1379 kPa) (0 to 200 psi) to the end of the DEF air supply line. Go to step 11.
- Turn the ignition ON (key ON, engine OFF). Go to step 12.
- Using DiagnosticLink, perform the SCR air pressure test (60 second duration) while monitoring the air pressure gauge. Is the air pressure between 517 to 586 kPA (75 to 85 psi)?
- Yes; remove the air pressure gauge and reconnect the air supply line to the DEF pump. Go to step 14.
- No; Go to step 13.
- Inspect PLU for contamination. Is there any debris, oil or coolant present in the PLU?
- Yes; diagnose and repair the cause of the contamination. Refer to section "Inspection of the Diesel Exhaust Fluid Compressed Air Flow System after Air Compressor Failure" and Technical Service Letter 12 TS-16Rev. Verify repair.
- No; replace the PLU. Verify repair.
- Disconnect the DEF tank return line (1) from the DEF pump (2). Refer to section "Removal of the Diesel Exhaust Fluid Line Connections" .
- Observe the DEF tank return outlet fitting on the pump while running the SCR air pressure test (60 second duration). Is there fluid discharge from the pump return outlet during the SCR air pressure test?
- Yes; replace the DEF pump pneumatic pump switch valve. Refer to section "Removal of the Diesel Exhaust Fluid Pump Module Pneumatic Switching Valve" .
- No; reconnect the DEF pump tank return line. Go to step 16.
- Disconnect the DEF pump inlet line. Attach a clear rubber hose over the DEF pump inlet port and place the other end of the hose in a clean container with fresh water. Go to step 17.
- Perform the SCR air pressure test while monitoring the DEF pressure. Does the DEF pressure reach 496 kPa (72 psi)?
- Yes; Go to step 18.
- No; replace the DEF pump. Refer to section "Removal of the Diesel Exhaust Fluid Pump Module" . Verify repair.
- Inspect the DEF pump suction line for damage or restrictions. Is the DEF pump suction line damaged or restricted?
- Yes; replace the DEF pump suction line. Refer to section "Removal of the Diesel Exhaust Fluid Lines (Tank to Pump)" . Verify repair.
- No; inspect the DEF tank header for restrictions. Repair as necessary. Verify repair.
Printed Thu Jun 02 2016 07:16:42 GMT-0400 (Eastern Daylight Time)
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