DEF Tank

This procedure covers the removal and replacement of the Diesel Exhaust Fluid (DEF) tank on a 2007 Ram 3500 with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• DEF tank assembly × 1 — Use OEM specification
• DEF tank mounting strap bolts × 4 — Use OEM specification
• DEF supply line quick-connect seal × 1 — Use OEM specification
• DEF return line quick-connect seal × 1 — Use OEM specification
• DEF tank level sensor O-ring × 1 — Use OEM specification

Fluids

• Diesel Exhaust Fluid (DEF) — 10 qt

Preparation

1. Verify the vehicle actually has a DEF system installed, as 2007 5.9L Cummins engines did not come equipped with DEF from the factory
2. Park vehicle on level ground and engage parking brake
3. Place wheel chocks behind rear wheels
4. If DEF system is present, allow engine to cool completely if recently operated
5. Disconnect negative battery cable to prevent electrical issues during service
6. Raise rear of vehicle using floor jack and support securely on jack stands
7. Locate DEF tank, typically mounted on driver side frame rail behind rear axle
8. Spray all mounting bolts and connections with penetrating oil and allow to soak for 15 minutes

Procedure

1. 1

   Drain DEF tank
   Determine the drain method for the installed tank. Many DEF tanks lack a bottom drain plug and must be emptied with a transfer/siphon pump or through the sender opening. If a drain plug is present at the bottom of the tank, position a clean drain pan and remove it. Position a clean drain pan underneath. Remove the drain plug and allow all DEF fluid to drain completely into the pan. DEF can be reused if clean and uncontaminated. Store drained DEF in a sealed, labeled container away from direct sunlight.
2. 2

   Disconnect electrical connector
   Locate the electrical connector for the DEF tank level sensor on top of the tank. Press the release tab and pull the connector straight off. Inspect connector terminals for corrosion or DEF crystallization and clean if necessary with electrical contact cleaner.
3. 3

   Disconnect DEF supply line
   Locate the DEF supply line (larger line) connected to the tank. Press the quick-connect release tabs on both sides simultaneously while pulling the line away from the tank fitting. Some residual DEF will drain out, so have a rag ready. Inspect the quick-connect for damage or excessive wear.
4. 4

   Disconnect DEF return line
   Locate the DEF return line (smaller line) connected to the tank. Press the quick-connect release tabs and remove the line from the tank fitting. Cap or plug both disconnected lines to prevent contamination and DEF crystallization in the supply system.
5. 5

   Disconnect DEF vent line
   Locate the vent line at the top of the DEF tank. This is typically a smaller diameter hose with a barbed fitting. Loosen the hose clamp using a flathead screwdriver or socket, then twist and pull the vent hose off the tank fitting.
6. 6

   Remove tank mounting strap bolts
   Locate the metal straps securing the DEF tank to the frame rail. Support the tank with one hand or have an assistant hold it. Remove the mounting strap bolts using the appropriate socket. The number of straps and bolts will depend on the specific (likely aftermarket) mounting configuration, so verify before removal. Keep track of any spacers or washers on the bolts.
7. 7

   Lower and remove DEF tank
   Carefully lower the DEF tank while ensuring no lines or wires are still attached. Guide the tank down and out from between the frame rails. Inspect the tank mounting area on the frame for corrosion or damage. Clean mounting surfaces with a wire brush if needed.
8. 8

   Inspect and clean components
   Inspect all quick-connect fittings, mounting hardware, and the tank mounting location. Replace any damaged quick-connects or seals. Clean any DEF residue or crystallization from fittings and mounting hardware. Wire brush the mounting straps and hardware to remove rust.
9. 9

   Install new DEF tank
   Position the new DEF tank between the frame rails in the mounting location. Align the mounting strap holes with the tank and frame mounting points. Ensure the tank filler neck is oriented correctly toward the access point.
10. 10

    Install mounting straps and hardware
    Position both mounting straps over the tank. Install all four mounting bolts with any spacers or washers in their original positions. Hand-tighten all bolts first, then torque to specification working in a cross pattern to ensure even clamping pressure. Torque values cannot be verified for this application. If this is an aftermarket DEF installation, use the tank/strap manufacturer's specified torque; strap bolts of this size are typically in the 15-25 ft-lbs range, but confirm before final tightening to avoid crushing plastic straps or the tank.
11. 11

    Connect DEF supply and return lines
    Install new quick-connect seals if provided with the replacement tank. Push the DEF supply line (larger) onto the tank fitting until you hear and feel a distinct click. Tug on the line to verify it is locked. Repeat for the return line (smaller). Ensure both lines are fully seated.
12. 12

    Connect vent line and electrical connector
    Push the vent hose onto the tank vent fitting and secure with the hose clamp, positioning the clamp past the barbed section. Tighten the clamp securely. Connect the electrical connector to the DEF tank level sensor, ensuring it clicks into place.
13. 13

    Fill DEF tank and check for leaks
    Fill the DEF tank with fresh Diesel Exhaust Fluid through the filler neck to the manufacturer's specified capacity, leaving headspace for thermal expansion. Verify the actual tank capacity for the installed unit, as it is not a factory component on this vehicle. Inspect all connections for leaks. Wipe down any spilled DEF immediately to prevent crystallization.

Reassembly

1. Reconnect negative battery cable
2. Lower vehicle from jack stands
3. Remove wheel chocks
4. Dispose of old DEF tank and contaminated DEF according to local environmental regulations
5. Clean all tools that contacted DEF with water to prevent crystallization

Verification

• Start the engine and verify the DEF system does not display any warning lights or fault codes
• Check the instrument cluster to confirm DEF level reading is displayed correctly
• Perform a visual inspection underneath the vehicle for any DEF leaks at connections or the tank
• Allow engine to reach operating temperature and verify the DEF system operates normally without warnings
• Test drive vehicle and monitor for any DEF system warnings or messages
• Re-inspect all connections after test drive for signs of leakage

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