5509696RX | Genuine Cummins® Inlet Catalyst Module X15 / ISX15

1. Compatible Engine Platforms

Part number is used in heavy-duty commercial vehicles with Single Module™ emissions systems:

• Cummins® Engine Platforms: X15 (Performance & Efficiency Series), ISX15 (Late EPA 2017), L9, and ISL9 engines.

2. Vehicle Fitment

This remanufactured inlet catalyst fits a wide range of Class 7 and Class 8 trucks:

• Freightliner: Cascadia 116/126, Coronado, and 122SD.

• International / Navistar: LT Series, RH Series, LoneStar, and HX Series.

• Peterbilt: 579, 389, 567, and 520.

• Kenworth: T680, T880, W900L, and C500.

• Western Star / Volvo: 49X, 57X, and select heavy-duty custom chassis.

1. What is it?

Part is a stainless steel inlet canister that houses the Diesel Oxidation Catalyst (DOC). Positioned directly downstream of the turbocharger downpipe, it receives raw exhaust gas from the engine and chemically alters it before it passes into the downstream Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) stages. The "RX" suffix designates a factory-remanufactured Genuine Cummins® ReCon® unit built to exact OEM performance specifications.

2. Core Functions & Features

• Hydrocarbon Oxidation & Thermal Management: Converts unburned hydrocarbons (HC) and carbon monoxide (CO) into water vapor and carbon dioxide (CO2), producing the heat required to trigger and sustain active DPF regenerations.

• Nitric Oxide Oxidation: Oxidizes nitric oxide (NO) into nitrogen dioxide (NO2), optimizing the balance required for effective passive soot oxidation in the DPF and efficient NOx reduction in the SCR.

• Integrated Sensor Ports: Precision-threaded bosses accommodate the upstream inlet NOx sensor, inlet Exhaust Gas Temperature (EGT) sensor, and DPF differential pressure port.

1. Failed Active DPF Regenerations & Frequent Derates

• Symptom: The engine repeatedly triggers active DPF regeneration cycles but fails to complete them, resulting in rapid DPF soot accumulation, severe engine power derates, or shutdown warnings.

• Cause: A degraded or face-plugged Diesel Oxidation Catalyst (DOC) can no longer exothermically react with dosed fuel to elevate exhaust temperatures to the required ~1,000°F (550°C) target.

2. Check Engine Light & Diagnostic Fault Codes (DTCs)

The Engine Control Module (ECM) closely monitors the temperature differential across the module and will trigger active fault codes:

• Common Diagnostic Trouble Codes (DTCs):

  • SPN 4331 / FMI 18 (Aftertreatment 1 Diesel Oxidation Catalyst Efficiency - Below Normal)

  • SPN 3251 / FMI 0 or 15 (Aftertreatment DPF Differential Pressure - High / Very High)

  • SPN 4765 / FMI 2 (Aftertreatment 1 DOC Intake Temperature - Data Erratic)

3. Excessive White Smoke or Raw Fuel Smell During Regeneration

• Symptom: Dense white or grey smoke and a strong smell of unburned diesel vapor coming from the exhaust pipe during an active regeneration attempt.

• Cause: Raw fuel injected into the exhaust stream passes through the DOC unoxidized because the catalytic coating is spent, poisoned, or coated in soot/oil.

4. Engine Hesitation & High Exhaust Backpressure

• Symptom: Significant turbo lag, loss of pulling power under load, and reduced fuel economy.

• Cause: Physical plugging of the DOC substrate face (from leaking turbocharger oil seals or coolant leaks) chokes total engine exhaust flow.