Over Pressurized DEF System
SPN 4374/FMI 1
Description Over Pressurized Diesel Exhaust Fluid (DEF) System
Monitored Parameter DEF Pump Speed vs. DEF Pressure
Typical Enabling Conditions DEF Pump Enabled OR On-Off-Cycle Request
Monitor Sequence None
Execution Frequency Continuous When Enabling Conditions Met
Typical Duration 2 Minutes
Dash Lamps MIL, CEL
Engine Reaction None
Verification ADS Self-check

Check as follows:

Show/Hide Checkboxes
1. Connect DiagnosticLink® .

2. Turn the ignition ON (key ON, engine OFF).

3. Check for multiple codes. Are any other faults active in addition to SPN 4374/FMI 1?1. Yes; Diagnose and repair the other faults first. Verify repair.
2. No; Go to step 4.

4. Verify the Aftertreatment Control Module (ACM) software level is e5.57.0.0 or newer. Compare the current ACM software level to the server. Is the ACM software at the latest level?
1. Yes; Go to step 5.
2. No; update the ACM software level and perform the verification procedure in the table above. If the fault code does not return, release the vehicle. If the fault code returns, Go to step 5.

5. Turn the ignition OFF.

6. Disconnect the DEF dosing unit electrical harness connector.

7. Inspect the DEF dosing unit electrical harness wiring and connector for signs of damage, bent, spread, corroded or unseated (pushed out) pins, moisture in the connector or wire damage near the connector. Is any damage found?
1. Yes; repair as necessary. Perform Selective Catalytic Reduction Airless Dosing System (SCR ADS) Self-Check Routine to verify repairs.
2. No; Reconnect harness connector. Go to step 8.

8. Disconnect the DEF return line from the DEF dosing unit. Refer to section “Removal of the GHG14 Diesel Exhaust Fluid Lines” . Connect a temporary drain hose from the DEF dosing unit return fitting into a DEF-safe container.

9. Clear fault codes.

10. Perform SCR ADS Self-Check Routine. Did the SCR ADS test pass with flow from dosing unit return line into the DEF-safe container?
1. Yes; Replace DEF return line. Go to step 11.
2. No; replace DEF dosing unit. Refer to section “Removal of the GHG14 Dosing System Doser” . Verify repair.

11. Reconnect all DEF lines and connectors. Perform SCR ADS Self-Check Routine to prime the system. Did the SCR ADS Self-Check Routine complete successfully?
1. Yes; release vehicle.
2. No; replace DEF dosing unit.