Truck Fault Codes

Detroit DD13 SPN 3361 FMI 1 — DEF Supply Pressure Below Normal

SPN 3361 FMI 1 on a Detroit DD13 means DEF supply pressure is below the normal threshold. The DEF supply pump is not generating sufficient pressure to deliver DEF to the dosing injector. Check the DEF filter for restriction, inspect the supply lines, and confirm DEF level and quality. If lines and filter are clear, the DEF pump may be failing. Use Detroit DiagnosticLink to monitor DEF supply pressure.

Code Details

Structured details for SPN 3361 FMI 1
Display codeSPN 3361 FMI 1
SPN3361
FMI1
OEM codeNone listed
ManufacturerDetroit Diesel
SystemAftertreatment — DEF supply system
ComponentDEF supply pump / DEF lines / filter
Source addressUnknown or not applicable
Severitymedium
Review statussource backed
Source confidencemedium
Last reviewed2026-06-12

Plain-English Meaning

The DD13 DEF supply pump draws fluid from the tank and pressurizes it for delivery to the dosing injector. When supply pressure falls below the normal range, DEF delivery becomes unreliable or stops, causing the SCR system to fail to reduce NOx adequately. Low supply pressure on the DD13 is most often caused by a plugged DEF filter, a frozen or blocked supply line in cold weather, or a failing supply pump. Diagnosing and restoring proper supply pressure is necessary to prevent the SCR inducement sequence from advancing.

SPN 3361 is related to Aftertreatment DEF Dosing Unit Pressure in J1939. FMI 1 indicates a valid reading below the normal operational range. On Detroit GHG17 DD13 engines, the DEF supply pump module draws from the tank and maintains the supply pressure required by the dosing injector. The ACM2 monitors this pressure and logs SPN 3361 FMI 1 when the value falls below the calibrated minimum. DiagnosticLink can display commanded and actual DEF pump pressure in real time, which helps distinguish a restriction in the supply path from a pump output failure.

Common Symptoms

  • SCR efficiency fault or NOx conversion warning alongside this code
  • DEF dosing quantity below commanded level in DiagnosticLink data
  • DEF system warning on the instrument cluster or Virtual Technician alert
  • In cold weather, may occur after a DEF freeze-thaw cycle if lines are still partially blocked
  • Inducement sequence may begin if the supply pressure fault persists

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

  • DEF supply filter plugged with debris or contamination
  • DEF supply line kinked, blocked, or partially frozen in cold weather
  • DEF supply pump motor worn or failing
  • DEF pressure sensor fault reading low
  • DEF check valve in the pump module stuck or failed

First Checks

  • Check DEF filter condition and replace if overdue or if contaminated DEF has been used
  • In cold-weather conditions, allow the full DEF system warm-up cycle to complete before evaluating the fault — partially frozen lines clear as the system heats
  • Connect Detroit DiagnosticLink and monitor DEF supply pressure during a pump activation cycle
  • Inspect DEF supply lines from the tank module to the dosing injector for kinks, crushes, or blockage
  • Verify DEF quality and level are adequate — contaminated or low DEF can contribute to pump and filter issues
  • If pressure remains low with clear lines and a good filter, test the DEF supply pump module for adequate output

Can I Keep Driving?

The DD13 can operate with SPN 3361 FMI 1 active initially, but inadequate DEF delivery will reduce SCR efficiency and trigger the inducement sequence. Repair the supply pressure fault promptly to prevent escalation.

SPN 3480 FMI 5Aftertreatment — DEF dosing system · DEF dosing injector / wiring circuit

Related Lookup Pages

Sources

  • Detroit Diesel Service and Diagnostic Resources — Public Reference Detroit Diesel (Daimler Truck North America) · oem · accessed 2026-06-11 · confidence medium

    Source: Detroit Diesel (Daimler Truck North America), Detroit Diesel Service and Diagnostic Resources — Public Reference. This page paraphrases factual fields only and is not a substitute for the original document.

    Open source
  • SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium

    Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.

    Open source

FAQ

How often should the DEF filter be replaced on the Detroit DD13?

Detroit Diesel specifies DEF filter replacement as part of the scheduled maintenance program. The filter interval is typically tied to mileage or engine hours and is listed in the DD13 service documentation. Using ISO 22241-compliant DEF reduces filter contamination rates. When servicing for a DEF supply pressure fault, replacing the DEF filter is a cost-effective first step before pursuing further diagnosis of the pump or lines.

Can frozen DEF cause SPN 3361 FMI 1 on the Detroit DD13 even with the heater working?

Yes, in extreme cold conditions. The DEF heater circuit requires time to thaw the tank, lines, and pump module after a cold soak. If the ECM begins requesting DEF dosing before the supply path is fully thawed, supply pressure will be low and this code may set temporarily. Allowing additional engine warm-up time before expecting full DEF system operation is the appropriate response for a first-occurrence pressure fault in very cold weather.

Is the DD13 DEF supply module the same as the DD15?

The Detroit GHG17 DD13 and DD15 share the same aftertreatment architecture and many DEF system components. The supply module design and service procedures are similar between the two engines. Part numbers may differ by engine displacement or production year, but the diagnostic approach using DiagnosticLink is the same for both engines.