NHTSA lists 2 safety recalls and 69 owner complaints for the 2003 Mitsubishi Diamante. Most complaints involve visibility (30) and engine and engine cooling (18). The EPA rates it 18 mpg combined.
CERTAIN PASSENGER VEHICLES FAIL TO CONFORM TO THE REQUIREMENTS OF FEDERAL MOTOR VEHICLE SAFETY STANDARD NO. 208, 'OCCUPANT CRASH PROTECTION.' THE BILINGUAL ENGLISH/SPANISH REMOVABLE AIR BAG WARNING LABELS AFFIXED TO THE DASH AND TO THE SUNVISOR DO NOT MEET THE SIZE REQUIREMENTS OF THE STANDARD.
CERTAIN SPORT UTILITY AND PASSENGER VEHICLES FAIL TO COMPLY WITH FEDERAL MOTOR VEHICLE SAFETY STANDARD NO. 225, "CHILD RESTRAINT ANCHORAGE SYSTEMS." THE OWNER'S MANUAL DOES NOT CONTAIN A STEP-BY-STEP DESCRIPTION FOR HEADREST ADJUSTMENT WHEN INSTALLING A CHILD RESTRAINT SYSTEM (CRS) TETHER STRAP.
Complaints are unverified owner reports to NHTSA and are not normalized for sales volume. One complaint can cite several components.
“INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6). THIS CONCERNS MY 2003 MITSUBISHI DIAMANTE. IT HAS LESS THAN 50,000 MILES ON IT AND IT HAS SUDDENLY STARTED SPEWING A LIGHT FILM ON THE INSIDE OF MY FRONT WINDSHIELD SO THAT I CANNOT SEE WELL...AND NOT AT ALL WHEN I AM HEADED INTO THE SUN. I HAVE CHECKED ON THE INTERNET AND A LOT OF PEOPLE ARE HAVING THE SAME PROBLEM WITH MITSUBISHI DIAMANTES GOING BACK SEVERAL MODEL YEARS. ALL DIAMANTES NEED TO BE RECALLED AND THE HEATER CORE AND/OR ITS O RINGS FIXED OR REPLACED. IF THIS DOESN'T HAPPEN, PEOPLE WILL DIE WHEN THEY SUDDENLY CANNOT SEE THE ROAD THROUGH THEIR FRONT WINDSHIELD. [XXX] *TR *DT”
“I HAVE A 2003 MITSUBISHI DIAMANTE LS WITH 71677 MILES ON IT ALL OF THE SUDDEN MY HUSBAND (THE PRIMARY DRIVER) TELLS ME THAT EVERY TIME HE GETS OUT OF THE CAR HE FEELS LIGHT HEADED AND NAUSEOUS. DAYS LATER THE FRONT WINDSHIELD STARTED FOGGING UP WHILE DRIVING AND AFTER TURNING THE CAR OFF (WHETHER IT IS WARM OR COLD OUTSIDE) I GOOGLED WHY WOULD THIS HAPPEN AND HAVE SPOKEN WITH A FEW MECHANICS AND THEY ARE TELLING ME THAT IT IS THE HEATER CORE GOING OUT, AND THAT THE REASON WHY MY HUSBAND IS GETTING LIGHT HEADED AND NAUSEOUS IS BECAUSE THERE IS ANTI-FREEZE COMING INTO THE INTERIOR OF THE CAR WHICH IS VERY DETRIMENTAL TO YOUR HEALTH. I HAVE READ A TON OF COMPLAINTS ON DIFFERENT WEBSITES AND THEY ALL SAY THE SAME THING. I CONTACTED MITSUBISHI CORPORATE TODAY AND SPOKE WITH A [XXX] IN CUSTOMER SERVICE AND EXPLAINED TO HER WHAT WAS GOING ON AND ASKED WHY MITSUBISHI HAS NOT DONE ANYTHING ABOUT THIS. FIRST BECAUSE OF THE HEALTH IMPLICATIONS, SECONDLY BECAUSE OF THE SAFETY ISSUE OF THE WINDSHIELD FOGGING UP WHILE YOU'RE DRIVING TO WHERE YOU CAN'T SEE AND THIRDLY THAT FROM READING THE COMPLAINTS, THE HEATER CORE IS RIGHT ABOVE THE COMPUTER IN THE CAR SO IF THE HEATER…”
“TL* THE CONTACT OWNS A 2003 MITSUBISHI DIAMANTE. THE CONTACT STATED THAT THE HEATER CORE FLUID LEAKED ONTO THE CENTRAL COMPUTER AND CAUSED THE TRANSMISSION TO FAIL. IN ADDITION, THE GEAR SHIFTER COULD NOT BE RELEASED FROM THIRD GEAR. THE VEHICLE WAS NOT TAKEN TO THE DEALER. THE VEHICLE WAS NOT REPAIRED. THE MANUFACTURER WAS MADE AWARE OF THE FAILURE. THE APPROXIMATE FAILURE AND CURRENT MILEAGE WAS 164,000. THE VIN WAS NOT AVAILABLE.”
Towing, payload and dimensions aren’t in the EPA or NHTSA data, so we don’t list them.
| Version | City | Hwy | Comb. | Fuel / yr | CO₂ g/mi |
|---|---|---|---|---|---|
| Diamante Sedan Auto 4-spd, 6 cyl, 3.5 L · Front-Wheel Drive | 16 | 23 | 18 | $4,200 | 494 |
| Item | Miles | Time | Note |
|---|---|---|---|
| Engine oil & filter | 5,000–10,000 mi | 6–12 months | Follow the oil-life monitor if fitted |
| Tire rotation | 5,000–7,500 mi | Every oil change | Check pressure monthly |
| Engine air filter | 15,000–30,000 mi | 1–2 years | Sooner in dusty areas |
| Cabin air filter | 15,000–25,000 mi | 1–2 years | |
| Brake fluid | — | 2–3 years | Absorbs moisture over time |
| Coolant | 60,000–100,000 mi | 5–10 years | Long-life coolants last longer |
| Spark plugs | 60,000–100,000 mi | — | Iridium/platinum plugs at the long end |
| 12V battery | — | 3–5 years | Heat shortens battery life |
2 safety recalls as of Nov 12, 2026, according to NHTSA. Recall repairs are free at a dealer. Check your VIN to see whether your car is included and whether the repair was done.
Owners filed 69 complaints with NHTSA. The most-cited components are visibility (30), engine and engine cooling (18), power train (8). Complaints are unverified owner reports and aren't adjusted for how many cars were sold.
The EPA rates the 2003 Mitsubishi Diamante at 18 mpg combined, depending on engine and drivetrain (1 version rated).