Diesel Trouble Codes

Hard Start or No Start — Cummins ISX15

A concise diagnostic reference for hard start or no start on the Cummins ISX15 (2010–2017) with CM2250/CM2350 ECM and XPI high-pressure common rail.

Updated October 15, 2026

What’s going on

On the ISX15, hard start or no start usually means the XPI high-pressure common rail cannot build commanded rail pressure during cranking. The platform uses an electric lift pump feeding filters into a gear-driven high-pressure pump with a pump actuator, common rail, rail pressure sensor and high-pressure relief valve, and electronically controlled injectors. Low rail pressure from fuel supply restriction, air or water in fuel, a leaking relief valve, injector leakage, or a fuel pump actuator fault is typical for this symptom.12

Most likely causes

  1. Restricted fuel supply / plugged or water-contaminated fuel filters — Clogged primary/secondary filters or water in fuel starves the electric lift pump and high-pressure pump, causing low rail pressure and hard/no start. FC 559 may be present. FC 418 can indicate water in the fuel filter.123
  2. Failed or underperforming electric lift pump — Loss of lift pressure allows air ingress and prevents the high-pressure pump from priming. Typical codes are FC 2265 (voltage above normal/open) or FC 2266 (voltage below normal/shorted).145
  3. Air ingress or water in the fuel system — Air leaks on suction side or contaminated fuel cause erratic rail pressure and extended crank. Water detection is flagged by FC 418.13
  4. High-pressure relief valve leaking or not responding — A leaking or stuck rail pressure relief valve bleeds rail pressure, preventing start. FC 3727 indicates the relief valve is not responding as expected and often accompanies low rail pressure.16
  5. Fuel pump actuator / electronic fuel injection control valve fault — The XPI pump actuator controls rail pressure. A circuit or performance issue prevents commanded pressure. FC 2311 is the electronic fuel injection control valve condition code for this system.17

How to narrow it down

  1. Read and record all active and inactive fault codes.
  2. Inspect fuel filters for restriction, age, and water; check water-in-fuel indicator status; FC 418 points to water in the filter.
  3. Verify electric lift pump operation and circuit integrity; abnormal voltage conditions map to FC 2265 or FC 2266.
  4. Check for air ingress points on the suction side of the lift pump and filter housing; look for wetness, loose fittings, or damaged seals.
  5. Monitor rail pressure during cranking with a scan tool; low pressure vs. commanded pressure supports FC 559 and points to supply, relief valve, or pump actuator issues.
  6. Review recent fuel quality history and drain the fuel/water separator if contamination is suspected.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Fuel filter service$60–$2000.3–1 hrsEasy DIY
Rail pressure relief valve$50–$2000.5–1.5 hrsDIY with tools and a manual
Fuel pressure control valve (FCA/regulator)$100–$4000.5–2 hrsDIY with tools and a manual
Lift pump / fuel transfer pump$100–$4001–3 hrsDIY with tools and a manual

Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If rail pressure remains low after confirming supply and filters, or if high-pressure pump, relief valve, or injector testing is required, have a certified diesel technician perform further diagnosis. Do not service high-pressure fuel components without proper training and safety controls.

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 — Cummins ISX15 (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — Cummins ISX15 (curated) ↩︎ ↩︎

  3. Curated DTC seed — Cummins ISX15 (curated) ↩︎ ↩︎

  4. Curated DTC seed — Cummins ISX15 (curated) ↩︎

  5. Curated DTC seed — Cummins ISX15 (curated) ↩︎

  6. Curated DTC seed — Cummins ISX15 (curated) ↩︎

  7. Curated DTC seed — Cummins ISX15 (curated) ↩︎