Diesel Trouble Codes

Black Smoke Under Load — 6.7 Cummins (SCR / DEF)

Diagnostic reference for black smoke under load on 2013-present 6.7L Cummins SCR/DEF trucks.

Updated October 15, 2026

What’s going on

On a 6.7L Cummins with a working DPF, visible black smoke should not happen. It means soot is getting past a cracked or failed filter, usually on top of an engine making too much soot from low boost or an injector problem.1

Most likely causes

  1. VGT turbo underboost / sticking vanes or electric actuator fault — Low boost under load causes over-fueling and black smoke. The HE300VG is variable-geometry with an electric actuator and position sensor; no wastegate/vacuum/boost solenoid. Typical related code P0299.12
  2. Injector over-fueling / cylinder imbalance — A leaking or over-fueling injector creates excess soot under load. Typical related code P0263.1
  3. DPF cracked, failed, or removed — With a working DPF visible black smoke should not happen; a cracked or failed filter lets soot pass. Typical related code P2002.1
  4. Excessive soot generation from low boost combined with emissions derate — Low power conditions from turbo or fueling issues increase soot production; on this platform low power commonly involves the HE300VG turbo, fuel rail pressure, DPF restriction, or SCR/DEF derate.3

How to narrow it down

  1. Read stored trouble codes first; P0299, P226C, P0263, P2002 are related to this symptom on this platform.
  2. Check boost pressure vs. commanded under load; verify VGT actuator response and position sensor data. The HE300VG uses an electric actuator with position feedback and no wastegate/vacuum control.
  3. Inspect intake and turbocharger for restriction, vane sticking, or actuator fault; confirm MAP-based load control and that MAF is used for EGR/emissions only.
  4. Perform injector balance / cylinder contribution test; look for over-fueling or imbalance indicated by P0263.
  5. Inspect DPF integrity and backpressure; with a working DPF visible black smoke should not occur, so a cracked/failed filter allows soot passage, often with P2002.
  6. Review fuel system health: rail pressure, FCA/MPROP, in-tank supply pump, and rail pressure relief valve; low rail pressure can contribute to smoke under load.

Common mistake to avoid

Skipping the VGT actuator calibration. The 6.7 Cummins Holset actuator has to be relearned with a scan tool after it is replaced or disconnected, or boost control will stay off. Source: OBDAdvisor — diesel limp mode diagnosis.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Scan-tool forced (parked) regeneration—0.5–1.5 hrsDIY with tools and a manual
Fuel injector (each)$350–$7001–2 hrsShop
Electronic VGT actuator (needs calibration)$500–$1,4001–2 hrsDIY with tools and a manual
DPF replacement$1,500–$4,0001–4 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If high-pressure fuel pump failure is suspected with metal debris in the fuel system, stop diagnosis and have the system professionally inspected; high-pressure fuel work is safety-critical. See a pro for turbocharger removal, injector replacement, or DPF service.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

  1. Curated symptom seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎

  3. Curated symptom seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎