The Mack GU813's instrument cluster integrates a comprehensive suite of warning indicators tailored to its robust vocational design. These lights communicate real-time system status to prevent engine damage and ensure compliance with emission standards. Familiarity with each symbol is essential for maximizing uptime on job sites.
Mack GU813 Warning Light Symbols
| Symbol | Name | Color | What it means | What to do |
|---|---|---|---|---|
| Master Warning (Stop) | RED | A serious fault is detected – the GU813 may enter limp mode or could suffer drivetrain damage if ignored. | Immediately slow down, find a safe spot, and turn off the engine. Consult the driver display for the underlying code. | |
| Master Caution | AMBER | A non-critical system needs attention, such as a failed sensor or low fluid that isn't yet threatening the GU813's operation. | Check the message center and schedule service at the next stop. | |
| Check Engine (MIL) | AMBER | The GU813's ECM has detected an emission or performance issue, often related to the MPRO II engine or aftertreatment system. | Reduce load if possible, and have the fault codes read by a technician with Mack® diagnostics. | |
| Engine Oil Pressure | RED | Oil pressure has dropped below safe levels – this can lead to catastrophic engine failure on the GU813's heavy-duty MPRO series. | Shut down the engine immediately. Do not restart until oil level and pressure are verified. | |
| Battery / Charging | RED | The alternator is not charging or the battery voltage is below 11V, which may leave the GU813 stranded. | Turn off non-essential electrical loads and head to a service bay. Check alternator belt and connections. | |
| Coolant Temperature | RED | Coolant is overheating – typical causes include a stuck thermostat, low coolant, or a failing fan clutch on the GU813. | Pull over, let the engine idle in neutral for a few minutes, then shut down. Check coolant level after cooling. | |
| Transmission Temp | AMBER | The mDRIVE™ (or automated manual) transmission fluid is too hot, reducing clutch life and shift quality. | Reduce load or gear down to increase airflow. If persistent, check for leaks or blocked cooler. | |
| Brake System | RED | A fault in the air brake system – could be low air pressure, a leak, or a failed modulator on the GU813. | Stop as soon as safely possible. Do not drive until air pressure rebuilds and no leaks are present. | |
| ABS | AMBER | The anti-lock brake system has a malfunction, which may affect stability during hard stops on the GU813. | Brakes still function normally but ABS not available. Have the system diagnosed at next service. | |
| Parking Brake | RED | The spring parking brake is engaged or pressure is too low to release it on the GU813. | Ensure air pressure is sufficient (above 100 psi) and release the yellow knob. If light stays on, inspect brake chamber. | |
| Tire Pressure (TPMS) | AMBER | One or more tires on the GU813 have pressure below the recommended threshold, affecting fuel economy and safety. | Check tire pressures at the next stop and inflate to 100 psi (steer) / 95 psi (drive) as per placard. | |
| Seat Belt | RED | Driver's seat belt is not fastened while the GU813 is in motion – a legal and safety requirement. | Buckle up immediately. The warning may be accompanied by an audible chime. | |
| Glow Plug / Preheat | AMBER | The intake air heater or glow plugs are active to aid cold starts on the GU813's diesel engine below 32°F. | Wait for the light to turn off before cranking – typically 5-15 seconds depending on oil temperature. | |
| DPF / Regeneration | AMBER | The diesel particulate filter needs a parked regeneration to clean soot buildup – the GU813 will prompt when exhaust temp is low. | Park the truck in a safe, well-ventilated area, engage parking brake, and press the regen switch per manual. | |
| DEF / AdBlue | AMBER | Diesel exhaust fluid level is low (below 10%) – the GU813 will eventually derate if ignored. | Add 2.5 gallons of DEF at the next fuel stop to avoid engine power reduction. | |
| Water in Fuel | AMBER | Water has accumulated in the fuel/water separator – can cause injector damage on the GU813's common-rail system. | Drain the separator (located on frame rail near fuel tank) following the drain procedure in the operator's manual. | |
| Low Fuel | AMBER | The GU813's fuel level is below 1/8 tank – you have approximately 20 gallons remaining in the 100-gallon tank. | Refuel as soon as possible. Running out of fuel can introduce air into the high-pressure fuel system. | |
| High Beam | BLUE | The high-beam headlights are on – use only when no oncoming traffic is present on the GU813. | Switch to low beams when approaching other vehicles to avoid glare. | |
| Air Brake Pressure (Low) | RED | Air pressure in the primary or secondary circuit is below 60 psi – the GU813's brakes may not release fully. | Stop immediately and let the engine run to build pressure to 120 psi. Check for air leaks before moving. | |
| High Exhaust Temp (HEST) | AMBER | Exhaust system temperature is elevated during active regeneration – the GU813 is cleaning the DPF. | No action needed. Avoid parking over dry grass. Light goes out when regen completes (usually 20-30 minutes). |
20 symbols shown. Icons follow ISO 2575 dashboard standards; exact graphics vary by model year.
Most Important Warning Lights
Engine Overheating
Common causes
- Low coolant level from a leak or air bubble
- Failed fan clutch or viscous fan drive
- Faulty thermostat stuck closed
What to do
On the Mack GU813, immediately reduce engine load and pull over. Let the engine idle for 2-3 minutes, then shut off. After cooling, check coolant level in the degas bottle (use only approved Mack coolant). If the fan does not engage when AC is on, replace the fan clutch.
Loss of Oil Pressure
Common causes
- Low oil level due to consumption or leak
- Clogged oil filter or pick-up tube
- Failed oil pump or pressure relief valve
What to do
Stop the engine immediately – do not restart. On the GU813's MPRO 13L, verify oil level with dipstick; top off with 15W-40 CJ-4 if low. If light remains, tow to service – internal engine damage may have occurred.
Air Brake System Failure
Common causes
- Compressor discharge line leak
- Failed brake chamber diaphragm
- Wet tank not draining causing ice in winter
What to do
Park on level ground and chock wheels. Build air pressure to 120 psi; if it drops more than 2 psi in one minute with engine off, find and fix the leak using soapy water on the GU813's air lines. Drain air tanks daily.
DPF Overload / Forced Regen Required
Common causes
- Excessive idling or low-load operation
- Soot accumulation due to short trips
- Failed exhaust gas temperature sensor
What to do
Drive at highway speeds for 30 minutes to initiate passive regen. If the amber DPF light remains, find a safe, open area and perform a stationary regen using the dash switch. Refer to Mack's driver guide for the GU813's specific procedure.
Low DEF Quality or Level
Common causes
- Using non-Mack approved DEF
- Contaminated DEF (dirty pump or container)
- Leaking DEF tank or lines
What to do
Fill with fresh DEF meeting ISO 22241. The GU813's SCR system will derate torque if DEF level drops below 2.5%. Check for crystallized deposits around the injector and clean with warm water. Replace DEF filter per maintenance schedule.
Frequently Asked Questions
What does the Master Warning (red stop) light mean on my Mack GU813?
It signals a critical fault—often low oil pressure or overheating—that requires you to stop the engine immediately to avoid severe damage. Refer to the message center for the exact code.
Can I continue driving with the Check Engine light on solid amber?
Yes, but only to the nearest service facility. The light indicates an emissions or performance issue that, if neglected, may cause a derate or failed inspection. Have the codes read by a Mack dealer.
Why does the DPF regen light come on even after a long highway trip?
The GU813 may still need a parked regen if the passive regen didn't complete due to low exhaust temperature. Ensure the DPF is not overloaded; if the light flashes, perform a stationary regen as described in the manual.
What should I do if the ABS warning light stays on after starting?
Safe braking is still possible, but ABS is disabled. Drive cautiously and schedule a diagnostic check. Common issues include a faulty wheel speed sensor or damaged tone ring on the GU813.
Is it safe to operate the Mack GU813 with the low air pressure warning on?
No. You need a minimum of 100 psi for the brakes to release fully. If the light stays on after building pressure, there's a leak. Stop and trace the air lines before continuing.