The Mack RD690 is a rugged vocational truck often used for dump, mixer, and heavy haul applications. Its instrument panel features classic analog gauges and warning lights designed for durability and simplicity in demanding environments.
Mack RD690 Warning Light Symbols
| Symbol | Name | Color | What it means | What to do |
|---|---|---|---|---|
| Master Warning (Stop) | RED | Illuminates red for critical issues like low oil pressure or brake failure, often accompanied by a buzzer on the Mack RD690. | Stop the vehicle safely and consult the warning page on the cluster. | |
| Check Engine (MIL) | AMBER | Indicates an engine or emissions fault that may reduce performance or fuel economy on your Mack RD690. | Have the diagnostic codes read at a Mack service center. | |
| Engine Oil Pressure | RED | Low oil pressure can cause severe engine damage; typical on the RD690 when oil level is low or pump fails. | Stop engine immediately and check oil level; if ok, do not restart. | |
| Battery / Charging | RED | Charging system problem, such as a failed alternator or loose belt, common on high-mileage Mack RD690 trucks. | Check belt tension and alternator connections; charge or replace battery if needed. | |
| Coolant Temperature | RED | Engine overheating due to low coolant, blocked radiator, or thermostat failure in the Mack RD690. | Pull over, let engine cool, check coolant level and leaks. | |
| Brake System | RED | On the Mack RD690, this warns of low air pressure, brake fluid leak, or parking brake engaged while moving. | Stop safely and inspect air pressure and brake connections. | |
| ABS | AMBER | Traction or anti-lock brake system fault, often due to a wheel speed sensor issue on the RD690. | Service the ABS system soon; braking remains functional but without assist. | |
| Parking Brake | RED | Indicates the parking brake is applied; on the Mack RD690, it also acts as a low-air warning if pressure drops. | Release parking brake before driving; if light stays on, check air pressure. | |
| High Beam | BLUE | High beams are on; common on the Mack RD690 for night driving on unlit roads. | Dim when approaching other traffic. | |
| DEF / AdBlue | AMBER | Low Diesel Exhaust Fluid level or quality issue; if ignored, the Mack RD690 will derate and eventually stop. | Refill DEF with fresh fluid from a reputable source. | |
| Water in Fuel | AMBER | Water detected in the fuel filter/water separator, common when using contaminated diesel on the RD690. | Drain water from the separator and replace the fuel filter. | |
| Low Fuel | AMBER | Fuel level is low, which can cause air in the system on the Mack RD690's mechanical injection pump. | Refuel as soon as possible to prevent engine stalling. | |
| Glow Plug / Preheat | AMBER | Indicates the glow plugs are heating for cold start; on the RD690, wait for light to go off before cranking. | Turn key to 'on' and wait until light extinguishes, then crank engine. | |
| Air Brake Pressure (Low) | RED | Air pressure below 60 psi; the Mack RD690's spring brakes will automatically apply if pressure drops further. | Stop and allow air pressure to build before moving; check for leaks. | |
| Trailer | GREEN | Trailer lights are connected and functioning; on the RD690, this light confirms trailer wiring is working. | Check if trailer ABS or marker lights are operational. |
15 symbols shown. Icons follow ISO 2575 dashboard standards; exact graphics vary by model year.
Most Important Warning Lights
Engine Overheat
Common causes
- Low coolant level
- Faulty thermostat
- Clogged radiator
What to do
Stop the Mack RD690 immediately, wait for engine to cool, then inspect and fill coolant; check for leaks and clean radiator fins.
Low Air Brake Pressure
Common causes
- Air leak in system
- Failed compressor
- Brake line damage
What to do
Do not drive; build air pressure with engine idling; if light persists, tow to a Mack service center for air system repair.
Oil Pressure Drop
Common causes
- Low oil level
- Oil pump failure
- Bearing wear
What to do
Shut off engine immediately; check dipstick and add oil; if light remains, do not restart—have the RD690 towed.
Charging System Failure
Common causes
- Alternator belt broken
- Alternator failure
- Wiring fault
What to do
Turn off non-essential electrical loads; drive only to nearest shop; replace belt or alternator on the Mack RD690.
DEF System Malfunction
Common causes
- Low DEF level
- DEF quality issue
- Sensor fault
What to do
Top off DEF with fresh fluid; if light persists, the RD690 may derate—schedule service to diagnose the SCR system.
Frequently Asked Questions
Why is my check engine light on but the truck runs fine?
On the Mack RD690, the check engine light (amber) can come on for minor emissions issues or sensor glitches; have the fault codes read to know if it's serious.
How do I reset the DPF regen light on an RD690?
For Mack engines, park the truck and activate the manual regeneration switch (if equipped) while idling; if light stays on, the filter may need cleaning.
What does the red 'STOP' light mean?
The red master warning on the Mack RD690 indicates a critical fault like low oil pressure or overheating—stop the engine immediately and investigate.
My ABS light stays on; can I still drive?
Yes, but without anti-lock assist; on the RD690, have the wheel speed sensors checked soon to prevent traction loss on slick roads.
How often should I drain the water from the fuel filter?
On the Mack RD690, check the water-in-fuel light; if it comes on, drain the separator immediately—preventively drain every oil change.
Why does the low air pressure light come on during start?
Normal on the RD690 if air pressure hasn't built up yet; wait for the gauge to reach 120 psi before releasing the parking brake.