Hard Start or Long Crank — 6.7 Cummins (SCR / DEF)
Diagnostic guide for hard start or long crank on 6.7 Cummins (SCR/DEF) 2013–present.
What’s going on
A long crank on the 6.7L Cummins is usually low fuel rail pressure from supply problems, air in the fuel or a fuel control actuator fault, or — in the cold — an intake air grid heater that is not working.1
Most likely causes
- Low fuel rail pressure from supply side or high-pressure pump control — Low-side supply pressure below expected can cause extended cranking and may set P008A. High-pressure side issues such as a fuel control actuator (FCA/MPROP) fault, air in fuel, or a stuck rail pressure relief/pressure-limiting valve can cause low rail pressure and may set P0087.1
- Intake air grid heater system performance — Cold-start hard start can be caused by the intake-air grid heater not performing as expected; the ECM monitors grid heater operation and may set P2609.12
- Fuel system air ingress or leak — Air entering the low-pressure supply or high-pressure circuit reduces rail pressure during cranking and prolongs start.1
How to narrow it down
- Read stored trouble codes and note freeze-frame data.
- Check low-side fuel supply pressure and in-tank supply pump operation; verify no restrictions or leaks in supply lines.
- Inspect high-pressure fuel system for air ingress, FCA/MPROP function, and rail pressure during cranking; compare to expected rail pressure.
- Test intake air grid heater system performance in cold conditions: verify relays, heavy cables/connections, heater element, and battery voltage while the heater runs.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Battery and charging voltage | 12.6–12.7 V at rest when fully charged; about 13.5 V running | Engine off, then running with loads on | DieselHub |
Parts and tools you may need
- Scan tool with Cummins enhanced data
- Fuel pressure gauge (low-side and rail)
- Multimeter
- Battery load tester
Tools you’ll need
- bi-directional scan tool — Reads stored codes, freeze-frame data, and commands the fuel control actuator and grid heater relay for active testing on the 6.7L Cummins.
- digital multimeter — Checks grid heater relay control voltage, heater element resistance, and battery voltage drop during heater operation in cold-start conditions.
- fuel pressure test kit — Measures low-side supply pressure and high-pressure rail pressure during cranking to confirm fuel supply and high-pressure pump control faults.
- clear tube fuel leak detector — Visually detects air bubbles in the low-pressure supply lines to identify air ingress causing long crank and low rail pressure.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Fuel filter service | $30–$150 | 0.3–1 hrs | Easy DIY |
| Intake grid heater relay | $40–$150 | 0.5–1 hrs | Easy DIY |
| Fuel supply or return line repair | $30–$200 | 0.5–2 hrs | DIY with tools and a manual |
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 rail pressure does not build during cranking, or if high-pressure fuel components are suspected, have a qualified diesel technician evaluate the system. Do not open high-pressure fuel components without proper training and safety equipment. If the grid heater shows signs of bolt deterioration or intake debris, have the intake inspected immediately to prevent engine damage.
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.
Related trouble codes
- P0087 — Fuel Rail/System Pressure Too Low
- P008A — Low Pressure Fuel System Pressure Too Low
- P0090 — Fuel Pressure Regulator Control Circuit
- P2609 — Intake Air Heater System Performance
Sources
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