Most common 2003 Mitsubishi Diamante problems
Share of the 56 complaints; one complaint can involve more than one system. "~" is the median mileage when the problem started.
Mitsubishi Diamante complaints by model year
Best Diamante years: 1995, 1999, 1998. Years to avoid: 2002, 2001, 2003, 2000. Compare all years →
2003 Mitsubishi Diamante recalls (2)
Equipment › Other › Labels
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.
Remedy: Mitsubishi caribbean will mail a customer notification letter containing a written description and a graphic of the bi-lingual dashboard air bag warning label.
Equipment › Other › Owners/service/other manual
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.
Remedy: A letter outlining the problem will be sent to owners along with a sticker containing the correct instructions as well as instructions on where to affix the sticker in the owner's manual.
What 2003 Mitsubishi Diamante owners say
A/C & heater all 27 →
Steering wheel began to shake and visible fumes began entering vehicle through air vents. There was a strong stench of anti-freeze. Check engine light was on and vehicle became hard to control. After taking car to local dealership, I was immediately told, even before an inspection was done, that the heater core on vehicle had a slow leak that over the course of "several months" that eventually leaked on to the transmission electric box and shorted out the entire system. It seemed obvious that this was a familiar issue with this particular vehicle. I was originally given an estimate of $3,300, being that the vehicle was past its warranty period. After several calls to owner of dealership and doing research on this vehicles complaint history, the price was reduced 3 separate times, finally costing me $880. …
For the past two years our car has had a very pungent fowl smelling odor when the air conditioner or heater is engaged that has gotten progressively worse. I took the car for repairs prior to the termination of the warranty and was told (by the dealership) that they did not notice a smell, and there was no problem. Six moths ago the car began to run hot and I took the car to our neighborhood mechanic. Under pressure he noticed a small leak in the coolant piping and replaced a section of pipe ($150.00). I asked if this could be causing the odor (as mentioned earlier and he stated maybe, or it could be the heater core).within the past two weeks the 'check engine soon' light has come on and upon checking the message and inspection of my car I've been told the heater core needs to be replaced. …
Engine & cooling
I own a 2003 Diamante Mitsubishi. The problem started with a check engine light coming on, fogging the window with a fowl toxic smell then the car would not hardly move out gear. I was told that the car's heater core leaked onto the computer which caused the transmission relay to short out do to the computer failing. The computer was still under warranty at 78,000 miles but I still had to pay for the new computer system because I was told that it was the heater core that caused the computer to fail. This is such a poor design! The computer should have been protected in such a case...funny thing it is now that I have had to replace a heater core, a computer and a transmission relay at a cut wrenching cost of $3,675.58. I wrote a letter to the president of north America Mitsubishi that the heater core should be a recall but to no avail. …
This is a Mitsubishi Diamante 2003 es. I'm experiencing a sweet smell of anti-freeze inside the car as soon as I turn on heating. Anti-freeze contains ethylene glycon and the fumes are highly toxic. Fixing the heater core will cost $1300. I am filing this complaint to ascertain that this is a very very common problem in Mitsubishi Diamante and Mitsubishi motors should be aware of three main risk associated with this: (1) the defect exposes customers to unusual level of toxic ethylene glycol which should not exceed 10-25 ppm levels (consult msds for ethylene glycol) (2) the leak can affect the car's microprocessor and poses a severe hazard for drivers. (3) faulty heater core makes the visibility difficult due to fogging of windshield thus putting the driver at greater risk. I will eventually fix the problem by spending $1300 if Mitsubishi refuses to issue a recall. …
Brakes
I have a new 2003 Mitsubishi Diamante, which I ve taken back to the dealership 3 times now with the same two issues: the front breaks make noise and my stearing wheel vibrates when I brake and the check engine service soon light keeps coming on. One of the dealer s employees told me that the brakes issues was very common as sometimes the cars sit for a long time in a lot before they are sold. This does not make feel safe driving this vehicle at this moment. The dealer will fix the light and brake issue assuring me that it s all fine now but the problem keeps coming back. I ve placed a call to the Mitsubishi motors company about this and they told me that they need to review the case to figure out what to do about it.
When I apply the brakes, the car shakes and jerks uncontrollably. I have had work done on the rotors as well as the brakes. I have four new tires, but problem still occurs. I am afraid that one day while driving this car the brakes will fail and cause my family and I serious injury . This is a 2003 Mitsubishi Diamante, and the incidents have occurred daily 3 months after I purchased the vehicle.
2003 Mitsubishi Diamante engines & fuel economy
| Engine | Transmission | Drive | MPG city / hwy / combined |
|---|---|---|---|
| 3.5L 6-cyl | 4-speed automatic | FWD | 16 / 23 / 18 |
EPA ratings. Class: Midsize car.
Frequently asked questions
Is the 2003 Mitsubishi Diamante a good car?
Based on 56 owner complaints filed with NHTSA, the 2003 Diamante rates use caution: 1.8× as many complaints as a typical year of the Diamante at the same age. It is one of the Diamante years we suggest avoiding. Complaint counts don't account for sales volume or individual maintenance, so have any used car inspected before buying.
What is the most common problem with the 2003 Mitsubishi Diamante?
The a/c & heater — 27 complaints, 48% of all complaints for this model year, most often about defroster/defogger/hvac system › heater core. Next are the engine & cooling (17) and brakes (5).
How many recalls does the 2003 Mitsubishi Diamante have?
There are 2 recalls for the 2003 Mitsubishi Diamante, the most recent from September 1, 2004 (labels). Recall repairs are free at any authorized dealer — check whether yours has been done with the VIN recall check.
What are the best and worst years of the Mitsubishi Diamante?
The best years by complaints, compared at the same age, are 1995, 1999 and 1998. Years to avoid or approach with caution: 2002, 2001, 2003 and 2000. See the full Mitsubishi Diamante years comparison.
At what mileage do 2003 Mitsubishi Diamante problems happen?
The median mileage reported in complaints is about 60,000 miles; 41% of problems with a recorded mileage started before 50,000 miles.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.