The RAM Cummins 2500 Big Horn's instrument cluster is tailored for its heavy-duty diesel operation, with specific warnings for the 6.7L Cummins engine. Red lights demand immediate attention, amber indicates caution, and green or blue signals active systems.
RAM Cummins 2500 Big Horn Warning Light Symbols
| Symbol | Name | Color | What it means | What to do |
|---|---|---|---|---|
| Master Warning (Stop) | RED | In the RAM Cummins 2500 Big Horn, this red warning indicates a critical issue that may require immediate engine shutdown, such as low oil pressure or overheating. | Safely pull over and turn off the engine; consult your owner's manual or contact service. | |
| Check Engine (MIL) | AMBER | This light in your Big Horn signals an emission or engine performance issue; it may be triggered by a loose fuel cap or a more serious fault in the Cummins diesel system. | Check the fuel cap first; if light persists, have the ECM codes read at a RAM dealer. | |
| Glow Plug / Preheat | AMBER | In cold conditions, this amber light on your 2500 Big Horn indicates the intake heater or glow plugs are warming the combustion chamber for easier starting. | Wait for the light to turn off before cranking the engine. | |
| Water in Fuel | AMBER | Your RAM Cummins 2500 Big Horn detects water contamination in the fuel system, which can damage the high-pressure injection pump on the 6.7L engine. | Drain the fuel/water separator immediately; refer to the owner's manual for the drain valve location. | |
| DPF / Regeneration | AMBER | This light indicates the diesel particulate filter is actively regenerating to burn off soot, a normal process for your Cummins diesel pickup. | Continue driving at highway speeds if safe; avoid frequent short trips to let regeneration complete. | |
| DEF / AdBlue | AMBER | The DEF level in your Big Horn is low or the system has a fault; exhaust aftertreatment requires DEF to reduce NOx emissions. | Refill with diesel exhaust fluid as soon as possible; if light stays on, have the system checked. | |
| ABS | AMBER | The anti-lock braking system on your RAM Cummins 2500 has a malfunction; standard brakes still work but ABS may not activate. | Drive cautiously and have the ABS system diagnosed at a service center. | |
| Brake System | RED | This red warning indicates a serious brake issue in your Big Horn, such as low brake fluid or a hydraulic failure. | Check brake fluid level immediately; if low, do not drive and call for a tow. | |
| Tire Pressure (TPMS) | AMBER | One or more tires on your 2500 Big Horn is significantly underinflated, affecting handling and fuel economy. | Check and inflate all tires to the recommended pressure, especially the rear duals if equipped. | |
| Reduced Power (Limp Mode) | AMBER | Your Cummins engine has entered a protection mode due to a detected fault, limiting power to prevent damage. | Pull over safely; restart the engine; if light stays on, have the vehicle serviced immediately. | |
| High Exhaust Temp (HEST) | AMBER | The exhaust system on your Big Horn is extremely hot, often during DPF regeneration, posing a fire hazard near dry grass. | Avoid parking over flammable materials until the light turns off. | |
| Transmission Temp | RED | The automatic transmission fluid in your 68RFE or Aisin transmission is overheating, risking transmission damage. | Stop and let the transmission cool; check for heavy loading or towing overload. | |
| Battery / Charging | RED | The charging system in your RAM Cummins 2500 is not maintaining battery voltage, often due to alternator failure. | Turn off non-essential electrical loads and drive to a service shop; or have the battery and alternator tested. | |
| Engine Oil Pressure | RED | Low oil pressure in your 6.7L Cummins can cause engine damage; this light is critical in the Big Horn. | Stop the engine immediately; check oil level; if full, do not restart and call for a tow. |
14 symbols shown. Icons follow ISO 2575 dashboard standards; exact graphics vary by model year.
Most Important Warning Lights
Check Engine Light (MIL)
Common causes
- Loose or faulty gas cap on the fuel tank
- Faulty oxygen sensor or diesel particulate filter sensor
- Emission system issue like high NOx or EGR malfunction
What to do
For your RAM Cummins 2500 Big Horn, tighten the fuel cap first; if light remains, have the ECM scanned at a dealer to pinpoint the fault specific to the 6.7L Cummins.
Brake System Warning
Common causes
- Low brake fluid level due to wear or leak
- Worn brake pads triggering the wear sensor
- Hydraulic failure in the brake booster or master cylinder
What to do
Check brake fluid reservoir; if low, top off and inspect for leaks. If pads are worn, replace them. For the Big Horn, any red brake light warrants immediate professional inspection.
Airbag (SRS) Warning
Common causes
- Faulty clock spring in the steering wheel
- Corroded wiring under the seat connections
- Deployed airbag from a previous accident not reset
What to do
Have the SRS system diagnosed at a RAM dealer; do not attempt DIY fixes as airbags can deploy unexpectedly in your 2500.
DPF Regeneration Light (Amber)
Common causes
- Frequent short trips preventing passive regeneration
- Clogged diesel particulate filter due to soot buildup
- Faulty exhaust temperature sensor or pressure sensor
What to do
Drive at highway speeds above 40 mph for 20-30 minutes to allow active regeneration. If light persists, your Big Horn may need a forced regeneration at a service center.
Low Oil Pressure Warning
Common causes
- Low engine oil level or incorrect oil viscosity
- Faulty oil pressure sending unit on the Cummins engine block
- Worn oil pump or clogged oil pickup screen
What to do
Stop the engine immediately. Check oil level with the dipstick. If oil is full, do not restart; have the oil pressure tested mechanically at a shop.
Frequently Asked Questions
Why does my glow plug light stay on longer in the RAM Cummins 2500 Big Horn?
In cold weather, the grid heater or glow plugs in the 6.7L Cummins may preheat for up to 15 seconds; this is normal. If it stays on while driving, it could indicate a fault in the intake heater relay.
What should I do when the 'Water in Fuel' light comes on?
Drain the fuel/water separator located on the driver side of the engine frame. On the Big Horn, turn the drain valve until clear diesel flows. If the light reappears frequently, replace the fuel filter.
My DEF light is amber; how much DEF do I need for my 2500?
The RAM Cummins 2500 holds about 5.5 gallons of diesel exhaust fluid. Refill at the DEF fill port under the fuel door; if level is low, the light will turn off after a few miles of driving.
Can I drive with the DPF regeneration light on?
Yes, continue driving normally; the truck will automatically regenerate the filter while you drive. Avoid stopping frequently during regen. If the light flashes, stop and have it serviced.
What causes the reduced power / limp mode on my Big Horn?
Common causes include a clogged DPF, faulty turbocharger actuator, or high exhaust temperature. Restarting the engine sometimes clears it; if persistent, a dealer scan is needed for the Cummins engine.
Is it normal for the transmission temp light to come on when towing heavy loads?
It can happen if the transmission (68RFE or Aisin) gets too hot. Reduce load or install an auxiliary cooler; on the 2500 Big Horn, pull over and let it idle to cool down.