exhaust

SCR Catalyst

for 2007 Ram 3500 5.9L I6 Cummins · 4WD

Difficulty

Moderate

Time

4.0 h

Tools

Steps

✓Fact-checked. Built from OLP's spec database, then independently fact-checked line by line with every correction applied. Master-tech sign-off by Chris Hackleman is queued. Cross-check torque values against the factory manual, and stop if anything looks unsafe. How our data is made.

This procedure covers the replacement of the Selective Catalytic Reduction (SCR) catalyst on a 2007 Ram 3500 with the 5.9L Cummins diesel engine.

Warnings

⚠️Exhaust system components remain extremely hot for extended periods after engine shutdown. Allow minimum 2 hours cool-down before beginning work to prevent severe burns.

⚠The SCR catalyst is heavy and awkward. Have assistance available when removing and installing to prevent injury or component damage.

⚠Do not contaminate DEF injector connections with dirt, oil, or debris as this will cause system failures.

ℹ️The 2007 Ram 3500 with 5.9L Cummins was the first year for SCR emissions equipment on this platform. Verify your specific vehicle is equipped with SCR before proceeding.

Tools required

Floor jack and jack stands rated for vehicle weightEssential

Wheel chocksEssential

Socket set (metric)Essential

Ratchet and extensionsEssential

Penetrating oil

Torque wrenchEssential

Exhaust hanger removal tool or pry bar

Wire brush

Safety glassesEssential

Work glovesEssential

Parts tray for hardware

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Parts

SCR catalyst assembly × 1 — Use OEM specification
Exhaust flange gasket (inlet) × 1 — Use OEM specification
Exhaust flange gasket (outlet) × 1 — Use OEM specification
Exhaust clamp or hardware kit × 1 — Use OEM specification
DEF injector O-rings × 1 — Use OEM specification
Temperature sensor O-ring (if equipped) × 1 — Use OEM specification

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Preparation

Park vehicle on level surface and apply parking brake firmly
Place wheel chocks behind rear wheels
Allow exhaust system to cool completely (minimum 2 hours after last engine operation)
Disconnect negative battery cable to prevent electrical issues during sensor disconnection
Raise vehicle using floor jack and support securely on jack stands at frame rails
Spray all exhaust clamps and fasteners with penetrating oil and allow to soak for 15-30 minutes

Procedure

1
Disconnect electrical connectors
Locate the SCR catalyst assembly underneath the vehicle between the DPF and tailpipe. Disconnect the electrical connector for the downstream NOx sensor by pressing the release tab and pulling straight out. Disconnect the DEF injector electrical connector in the same manner. Mark or photograph connector locations for reassembly reference.
2
Disconnect DEF supply line
Locate the DEF supply line connecting to the injector on the SCR catalyst. Use appropriate wrench to loosen the DEF line fitting. Capture any DEF fluid that drains with a suitable container. Cap or plug the DEF line to prevent contamination.
3
Remove downstream exhaust connection
Locate the exhaust clamp or flange connection at the outlet of the SCR catalyst (towards rear of vehicle). Remove clamp bolts or flange nuts. Separate the connection and slide the downstream exhaust pipe rearward slightly to create clearance. Support the exhaust pipe with a jack stand or secure with wire to prevent stress on other hangers.
4
Remove upstream exhaust connection
Locate the inlet flange connection between the DPF outlet and SCR catalyst inlet. Remove the flange nuts or clamp bolts securing this connection. Carefully separate the joint. If the connection is seized, apply additional penetrating oil and allow to soak, or use gentle heat if safe to do so.
5
Remove exhaust hanger supports
Identify all rubber exhaust hangers supporting the SCR catalyst assembly. Using an exhaust hanger tool or pry bar, carefully unhook each rubber isolator from its mounting bracket. Note the position and orientation of each hanger for proper reinstallation.
6
Remove SCR catalyst assembly
With all connections and hangers disconnected, carefully lower the SCR catalyst assembly from the vehicle. The unit is heavy and may require a second person or transmission jack for safe removal. Maneuver the assembly past the driveshaft and suspension components, taking care not to damage sensors or the DEF injector.
7
Inspect and clean mounting surfaces
Inspect the exhaust flange surfaces at both the DPF outlet and downstream pipe inlet for damage, warping, or excessive corrosion. Use a wire brush to clean all mating surfaces, removing old gasket material and carbon buildup. Inspect exhaust hangers for cracking or deterioration and replace if necessary.
8
Prepare new SCR catalyst
Remove new SCR catalyst from packaging and verify it matches the original unit. If reusing sensors, carefully remove the NOx sensor and any temperature sensors from the old catalyst, inspecting threads and connectors. Install sensors into new catalyst with new O-rings if provided. Do not overtighten sensors.
9
Install new exhaust gaskets
Position new exhaust flange gaskets at both the inlet and outlet connections of the SCR catalyst. Ensure gaskets are properly aligned with bolt holes and that the correct gasket type is used for each location. Some applications may use crush gaskets that must not be reused.
10
Position and install SCR catalyst
With assistance, lift the new SCR catalyst assembly into position under the vehicle. Align the inlet flange with the DPF outlet connection first, then maneuver the outlet end into position. Install exhaust hangers onto their rubber isolators, ensuring proper orientation and secure engagement.
11
Connect exhaust flanges
Install flange nuts or clamp bolts at the inlet connection between DPF and SCR catalyst. Tighten evenly in a cross pattern to pull flanges together squarely. Connect the outlet flange to the downstream exhaust pipe and secure with hardware. Tighten all fasteners evenly but do not fully torque until all connections are aligned.
12
Reconnect DEF supply line
Install new O-ring on DEF injector if provided in parts kit. Connect the DEF supply line to the injector fitting, ensuring threads engage properly. Tighten the DEF line fitting to manufacturer specification, being careful not to cross-thread the connection.
13
Reconnect electrical connectors
Reconnect the DEF injector electrical connector, ensuring it clicks fully into place. Reconnect the downstream NOx sensor electrical connector in the same manner. Verify all connectors are fully seated and locking tabs are engaged. Route wiring away from hot exhaust surfaces.
14
Final torque and inspection
Perform final tightening of all exhaust clamps and flange connections in sequence from front to rear. Verify all exhaust hangers are properly seated and supporting the system. Double-check that no wiring or DEF lines are contacting hot exhaust components or moving parts. Verify all tools and parts have been removed from under vehicle.

Reassembly

Reconnect negative battery cable
Lower vehicle from jack stands carefully
Start engine and allow to reach operating temperature while monitoring for exhaust leaks
Inspect all connections for leaks using visual and audible inspection
Use scan tool to clear any diagnostic trouble codes that may have been stored during replacement
Verify SCR system readiness monitors complete properly during test drive

Verification

Perform visual inspection of entire exhaust system for leaks while engine is running
Listen for exhaust leaks at all flange and clamp connections
Verify no DEF fluid leaks at injector connection
Use diagnostic scan tool to verify NOx sensor readings are within expected parameters
Confirm no check engine light or emissions warning lights are illuminated
Test drive vehicle to verify normal operation and DEF system functionality
Recheck all exhaust connections after first heat cycle and re-torque if necessary