Cummins fault code 4953

What it means

Cummins' description: Alternator 1 Status - Voltage Above Normal, or Shorted to High Source.

SPN 3353 is Alternator 1 Status. FMI 3 means the voltage on the circuit is higher than possible for a good sensor, usually an open signal wire, a short to a power wire, or a failed sensor.

The ECM needs clean, steady battery voltage, and it supplies regulated 5-volt power to many sensors. Voltage problems can cause strange codes across many systems at once.

What the lamp means

An amber (yellow) warning lamp means the engine can usually keep running, but the fault should be repaired soon, ideally the same day.

Common causes

FMI 3 is an electrical or signal fault, so start with the circuit:

• Loose or corroded battery cables or grounds
• Blown fuse or failed power relay
• Sensor supply shorted by one bad sensor or wire
• Damaged ECM power harness

If the circuit checks out, the reading may be real. Other possibilities: weak batteries; failing alternator; parasitic drain.

What you can check before calling

• Check battery terminals and ground straps for corrosion or looseness
• Have the batteries and alternator tested
• Note if several unrelated codes appeared at the same time

Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers. For the bigger picture, read our guide: Bad alternator or bad battery? How to tell.

Engines and sources

Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.