Buy Genuine CAT DEF Injector Assembly Side - wisentpartscenter.com

Description

Cat 371-1633 DEF Injector Assembly – Genuine Caterpillar Diesel Exhaust Fluid Doser

The Cat 371-1633 is a genuine Caterpillar DEF injector assembly, also called a doser injector. It is the last piece in the DEF system and the one that actually sprays fluid into the exhaust stream ahead of the SCR catalyst. The ECM tells 371-1633 how much to dose based on exhaust flow and temperature, and the spray pattern out of 371-1633 is what mixes the DEF into the exhaust so the catalyst can convert NOx the way it is supposed to. Used across Cat F series excavators, K and M series loaders and compactors, and C9.3 through C18 engines.

Key Functions:

- Sprays metered DEF into the exhaust stream ahead of the SCR catalyst
- Doses off ECM commands based on exhaust flow and temp
- Delivers the spray pattern the catalyst needs for proper NOx conversion

Fitment & Specifications:

- Genuine Cat DEF injector assembly, part number 371-1633
- Size: 5.0 in long, 3.0 in wide, 2.4 in high
- Excavators 336F, 340F, 349, 349F, 352, 352F, 374F, 390F, MH3295
- Compactors 825K, 826K, 836K
- Wheel loaders 966M, 972M, 980, 980M, 982, 982M, 986K, 988K and XE versions
- Off-highway trucks 770G, 772G
- Engines C9.3, C13, C15, C18

Verify fitment by machine or engine serial number before ordering.

Purpose of the Part

371-1633 is the injector that puts the DEF into the exhaust. Everything upstream of it, the tank header, the pump and the lines, is just getting fluid to this point. The ECM works out how much DEF the exhaust needs based on flow and temperature and commands 371-1633 to spray that amount. The spray pattern matters as much as the amount, the DEF has to atomize and mix into the exhaust evenly so it turns to ammonia and reacts across the whole catalyst. If 371-1633 is spraying heavy in one spot or dribbling instead of atomizing you end up with poor conversion and urea building up as crystal instead of burning off.

Issue Symptoms / When to Replace

The usual sign is an SCR efficiency code with the machine going into derate while everything else in the DEF system checks out fine. Crystallized urea around the tip of 371-1633 or in the exhaust pipe right after it is the classic one, that means it is not atomizing properly or it is leaking by. A plugged or restricted 371-1633 shows up as DEF pressure faults since the pump is pushing against a blockage, and a leaking one dumps fluid where it should not be and can wet stack the pipe. Machines that idle a lot are harder on these because the exhaust never gets hot enough to burn off deposits.

Before replacing 371-1633, check the fluid with a refractometer, look at the tank and filter for debris, verify the pump is building pressure and check the coolant side and connector if the machine uses them, all of that will throw similar codes.

Signs to look for are SCR and DEF fault lights, staged derate down to limp mode, crystal buildup around the injector and in the pipe, DEF pressure or dosing faults, wet spots or DEF residue at the mounting flange, and reduced power on grades.

Related codes may include:

- P20EE SCR NOx catalyst efficiency
- P207F DEF quality
- plus machine specific J1939 and CDL codes for DEF pressure, dosing and injector circuit faults

Brand Information

Caterpillar has been building heavy equipment for over 95 years with a parts catalog running past 1.4 million numbers. On a DEF injector this matters because the ECM doses off an assumed spray pattern and flow rate, and Cat builds 371-1633 to that calibration. A unit that sprays a little different will still bolt in and still leave the machine throwing SCR efficiency codes and derating. Cat parts are built for machines that sit in heat, vibration and dirt all day, which is exactly the environment this injector lives in.

Installation Notes

1. Take care of any engine, EGR, DPF or DOC faults first, SCR codes are usually coming from upstream.
2. Relieve the pressure in the DEF lines before you open anything up.
3. Pull 371-1633 and check the mounting boss and the pipe for crystal buildup, clean it all out before the new one goes in, dropping 371-1633 into a plugged pipe will just take it back out.
4. Check the DEF filter and look in the tank for debris while you are at it.
5. Install 371-1633 with new seals and gaskets, keep the fittings clean since DEF picks up contamination easy.
6. Torque the mounting hardware evenly and do not overtighten, the flange seals off the exhaust.
7. Reconnect the DEF line, coolant lines if equipped and the harness, make sure the plug is seated and locked.
8. Prime the system per the machine procedure so 371-1633 is not running dry on startup.
9. Clear codes, let it cycle and confirm dosing and pressure are reporting right before it goes back to work.

How to Identify an OEM Part

A genuine unit has the markings cast right into the side of the body, not printed on or stuck on with a label. You should see the Bosch name and logo, the Denoxtronic model, the Bosch part number, the OEM part number, a date code and the country of manufacture. Check that the numbers on the side match what you ordered and that the casting itself looks like an OEM unit.

Why Buy 371-1633 from Wisent Parts

  • ⏱️
    Fast shipping
    Orders before 12PM EST ship same business day.
  • 🛡️
    180-day warranty
    All parts covered from delivery date.
  • ↩️
    Easy returns
    30-day returns.
  • ✅
    Verify fitment
    Send VIN/ESN and we’ll confirm.

Shop with confidence

Warranty & Return Information
Warranty Information

Wisent Parts offers a 180-day warranty on all parts from the date of delivery. This warranty covers orders placed directly through our website. If a part fails during this period, we’re here to help - whether it’s a replacement, repair, or refund. For full details, refer to the Warranty page.

Return Information

Wisent Parts accepts returns within 30 days of delivery. All returns are subject to a restocking fee. To qualify, parts must be unused and in their original condition. For full return instructions and restocking fee details, please refer to the Returns page.