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2020 Ram 2500 Cummins No-Start Issue - Cranks but Won't Fire

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Kevin B. · rep 0 · May 22, 3:30 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Big Horn

Hello Ram owners,

I'm having a serious problem with my 2020 Ram 2500 Big Horn with the 6.7L Cummins diesel. This morning, it just cranks and cranks but won't start. No Check Engine Light is on, which is weird.

I've checked the battery, and it seems strong enough to crank the engine vigorously. I've also tried cycling the key a few times, thinking it might be a fuel prime issue, but no luck. It was running perfectly fine yesterday.

Could this be a fuel pump problem, a sensor, or something else entirely? Any advice on what to check first for a diesel no-start condition would be greatly appreciated. I'm stranded and need to get this beast running!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:30 AM

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ClearTheCode admin answer:

A crank-no-start condition on a 2020 Ram 2500 with the 6.7L Cummins can be frustrating, especially without a Check Engine Light. Diesels require three main things to start: compression, fuel, and air (with proper timing). Since it's cranking strongly, we can likely rule out a completely dead battery or starter. Here are common areas to investigate:

  1. Fuel System Issues: This is often the primary suspect in diesel no-starts.
    • Fuel Filter: A clogged fuel filter can restrict fuel flow. When was it last replaced? Try replacing it if it's due or if you suspect contaminated fuel.
    • Fuel Pressure: The Cummins engine relies on high fuel pressure. A failing lift pump (in-tank or frame-mounted) or high-pressure fuel pump (HPFP) could be the culprit. You'd need a scan tool to monitor actual vs. desired fuel rail pressure during cranking.
    • Air in Fuel Lines: If you recently ran very low on fuel or performed fuel system maintenance, air could be trapped. Cycling the key several times (allowing the lift pump to run) can sometimes help, but persistent air might require bleeding.
  2. Sensor Failure: Even without a CEL, a critical sensor could be failing.
    • Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP): If the engine computer doesn't know the engine's position, it won't know when to inject fuel or fire the injectors.
    • Fuel Rail Pressure Sensor: A faulty sensor could report incorrect pressure, preventing the ECM from commanding fuel injection.
  3. Injector Issues: While less common for a sudden complete no-start, one or more injectors could be stuck open or closed, preventing the engine from building enough compression or delivering fuel.

What to do:

  • Check Fuel Filter: Visually inspect or replace the fuel filter.
  • Listen for Lift Pump: Turn the key to the 'on' position (without cranking) and listen for the electric lift pump to hum for a few seconds. If you hear nothing, check its fuse/relay.
  • Scan for Pending Codes: Even without a CEL, there might be pending or historical codes that can point to a sensor issue.

When to see a shop:

If basic checks don't resolve the issue, it's time for professional help. A diesel specialist will have the necessary diagnostic tools to monitor live fuel pressure, injector pulse, and sensor readings. Diagnosing high-pressure diesel fuel systems requires specialized knowledge and equipment to avoid damage or injury.

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