Dodge RAM Cummins

Dodge RAM Cummins PCM (5.9L / 6.7L) — Troubleshooting Guide (SKU Group)

Important: Use this guide if you reinstalled your repaired Dodge RAM Cummins PCM and the problem is still happening.
Important: Please do not open/disassemble the PCM or force/probe connector pins (terminals can spread and cause new faults).

• Step 1: Confirm the correct module
  • Verify the PCM part number matches the original application (engine + year range).
  • If a replacement PCM was installed at any point, confirm it’s the correct calibration for the truck.
• Step 2: Battery, cables, and grounds
  • Load-test both batteries (weak batteries can cause no-start, no-comm, random warning lights).
  • Clean/tighten battery terminals and inspect the battery cables for hidden corrosion.
  • Inspect/clean engine-to-chassis and battery-to-chassis grounds.
• Step 3: Check PCM power fuses and ignition feeds
  • Check all ECM/PCM/IGN fuses in the under-hood and interior fuse boxes.
  • If a fuse is blown, do not keep replacing it—inspect wiring for chafing/shorts first.
• Step 4: Confirm relay operation
  • Verify the ASD/Main relay operation (clicks on at key-on and stays active while cranking).
  • Swap with a known-good matching relay (a weak relay can mimic a bad PCM).
• Step 5: Inspect PCM connectors and harness
  • Look for pushed-back pins, loose terminals, bent pins, corrosion/green buildup, or water intrusion.
  • Pay extra attention to areas where the harness rubs (near battery tray, fender, and engine bay edges).
• Step 6: If the complaint is “no start / starts then dies”
  • Check crankshaft position sensor and its connector/wiring (common cause).
  • Verify lift pump operation and fuel supply (air leaks/low supply pressure can prevent starting).
  • Verify rail pressure builds during crank (low rail pressure can be fuel system related, not PCM).
• Step 7: If the complaint is “no communication / won’t scan”
  • Confirm the diagnostic port has power and ground (a dead port looks like a dead PCM).
  • Verify CAN wiring integrity at the PCM area (damage/corrosion can block comms).
  • Disconnect recently-added accessories (remote start, audio, tuners) and re-check communication.
• Step 8: If the complaint is “reduced power / limp mode / shifting issues”
  • Scan for codes and address sensor/network codes first (MAP, crank, throttle-related, CAN, etc.).
  • Inspect connectors for sensors that were recently serviced (MAP, rail pressure, crank/cam).
• Step 9: If this started after repairs or wiring work
  • Re-check anything that was touched: grounds, battery connections, fuse/relay seating, sensor plugs, and harness routing.
• Step 10: Final verification that catches hidden issues
  • Have a shop perform voltage-drop tests on PCM power and grounds while cranking (finds hidden resistance a normal meter check can miss).