Six engine codes, three pumps and one very loyal fan base. Since 2001 the Duramax has run a Bosch CP3, then a Bosch CP4.2, then a Denso HP4, and the engine code on your truck tells you which one is bolted to yours.
This page lines up every Duramax by engine code and year, explains what each pump does in plain English and covers the problems that send them to our bench. We can help identify the system and discuss appropriate service options.
Which Pump Is on My Duramax?
| Model years | Engine code | High-pressure pump | What to know |
|---|---|---|---|
| 2001-2004 | LB7 | Bosch CP3 | The first Duramax; better known for injector trouble than pump trouble |
| 2004.5-2005 | LLY | Bosch CP3 | |
| 2006-2007 | LBZ | Bosch CP3 | A fan favorite for its toughness |
| 2007.5-2010 | LMM | Bosch CP3 | The last CP3 Duramax in pickups |
| 2011-2016 | LML | Bosch CP4.2 | Two plungers; sensitive to fuel quality, water and air |
| LGH, vans and chassis cabs | Bosch CP4.2 | Lower-output cousin of the LML | |
| Introduced 2017 | L5P | DENSO HP4 | Confirm the engine version and complete pump number; do not assume CP4 interchange |
Those half-years are real. GM changed engines mid-year more than once, so two trucks with the same model year can carry different engines and different pumps. The engine code settles it.
Bosch CP3 (LB7, LLY, LBZ, LMM): The Pump Behind the Legend
The CP3 is a radial-piston pump: three pistons around an eccentric cam, pushing fuel into the common rail at very high pressure. It does not time anything. The engine computer fires each injector; the CP3 just keeps the pressure up, and it has the muscle to spare.
Early Duramax fuel systems lean on the CP3’s internal gear pump to draw fuel from the tank, so an air leak on the suction side can make a healthy pump look sick. Most real CP3 failures trace to contamination or a sticking pressure regulator. Numbers start 0 445 020, and Bosch reman units start 0 986 437 3.
Bench Notes: The LB7 is famous for injector trouble, not pump trouble. If yours smokes, knocks or runs rough, have the injectors checked before you condemn the CP3.
Bosch CP4.2 (LML and LGH): Efficient and Unforgiving
The CP4.2 uses two plungers riding a cam through roller tappets. It is lighter and more efficient than the CP3, and with clean, dry fuel it is quiet and capable.
Its weakness is fuel quality. Poor lubricity, water or air can wear the internals, and once metal starts shedding it travels through the rail, lines and injectors. That is why an LML pump failure is often a whole-system repair. Numbers start 0 445 010. Read the CP4 failure guide for symptoms and the CP4 vs CP3 conversion guide if you are weighing a swap.
Shop Talk: Lubricity is a fuel’s ability to keep metal off metal. Pumps like the CP4.2 are lubricated by the diesel flowing through them, so fuel that is wet, dirty or thin on lubricity wears them from the inside.
Denso HP4 (L5P): New Maker, New Rules
For 2017, GM moved to a different supplier entirely. The L5P runs a Denso HP4, a three-plunger supply pump that delivers about one and a half times what Denso’s two-plunger HP3 does. It is not a CP4, and it does not share parts with one.
HP4 numbers start 294050-, and 294050-0701 is a common L5P number. The same family feeds Hino J08E trucks and the John Deere 9.0L, so it is no stranger to hard work. Clean, dry fuel is still the best insurance. See our Denso pump repair page for the whole family.
Did You Know? Denso was called Nippondenso until 1996, and it launched its first common-rail system in 1995, years before the first Duramax rolled out.
Common Duramax Pump Problems
- Low rail pressure codes such as P0087, or P0093 for a large leak, from air, clogged filters, a sticking regulator or a worn pump.
- Air in the system. Loose filter heads and cracked suction lines on early trucks.
- Water and contamination. Hard on every pump, hardest on the CP4.2.
- Hard starts and smoke. Our hard start and smoke guide helps sort pump from injector.
- Leaks. Aging seals and fittings. See our injection pump leaks guide.
How to Tell Which Pump You Have
Open the glove box and find the Service Parts Identification label. Among the three-character codes you will see LB7, LLY, LBZ, LMM, LML, LGH or L5P. Match it to the table above.
Then confirm on the pump tag: 0 445 020 is a CP3, 0 445 010 is a CP4 and 294050- is a Denso HP4.
Owner’s Tip: Scan for codes, change the fuel filter and drain the water separator before you blame the pump. Never crack a high-pressure line; common-rail pressure can injure.
Ship It Right: Cap every port, drain what you can and bag the pump. Write your engine code on the paperwork so we set up the right test plan.
Questions about Duramax Injection Pump Repair
Is the L5P pump a CP4?
No. The L5P uses a Denso HP4, a three-plunger pump from a different maker. The names sound alike, but the parts, numbers and repair procedures are different.
Should I convert my LML to a CP3?
Many LML owners do it for peace of mind, and it takes the right parts and calibration to do well. Read the conversion guide and use the repair inquiry form to talk it over.
My LB7 smokes and runs rough. Is it the pump?
On an LB7, injectors are the usual first suspect. Scan for codes and have the injectors balance-checked before you pull the CP3.
Do you work on the 3.0 Duramax?
Pump and system configurations vary. Provide the full pump number and engine details through the repair inquiry form so the available service options can be assessed.
Whether you drive an earlier LB7 or a later-model L5P, the fix starts the same way: on the bench, with real numbers. Start a Mail-In Repair or request a repair evaluation.