Which parts fail
Components named in complaints (engine, cooling system, oil leaks, timing chain, exhaust).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2002 Mitsubishi Diamante owners, lightly cleaned up (personal details are redacted by NHTSA).
Tl* the contact owns a 2002 Mitsubishi Diamante. The contact stated that while driving at 75 MPH, the contact attempted to brake but the brakes failed to respond without any warnings. The vehicle crashed into a passenger van. The vehicle was destroyed. The contact mentioned that two months prior to the failure the check engine light had illuminated. The vehicle was taken to an independent mechanic for diagnosis and was informed that the vehicle misfires, needed spark plugs, a fuel pump, a fuel injector, an EGR valve, and the engine surged erratically. The failure and current mileage was 140,000. Updated 12/06/12 updated 12/6/2012
This heater core leaks directly over computers which control the engine - and could cause it to act unpredictably or cut out altogether when driving. * anti-freeze contains ethylene gylcol which can cause serious respiratory damage * the leaking anti-freeze causes a film to form on the windshield, which can cause the windscreen to fog up suddenly, obscuring the view of the road and potentially causing a collision it will cost me more than 900.00 to repair this item, plus the cost to replace my carpet and to clean the interior of my vehicle. Plus I do not know if I will everget rid of the smell and this will most likely lower the resale value costing me even more in the long term.I would expect this kind of thing to happen to a car that is more than 10 years or old. …
This is the second time I am complaining about the same problem. The end of June 2006 I drove to work and reached down to pick some stuff up off the passenger side floor mat. It ended up being soaked. At first I thought some water had come in because the past few days our area had torrential rains. When I got home the next day I took up the floor mat to dry it out and notice all the liquid under it was greenish yellow. In my mind I went crazy because the same thing had happened to me a year and 2 weeks earlier. Once again the heater core became faulty and poured the engine coolant into the passenger spaces. Wonderful, since my wife was 8 months pregnant, great for her to be breathing those chemicals. I have to say I was fortunate that it didn't leak on any of the computer components, like has happened to others, especially while I was driving. …
The heater core is an extremely dangerous problem. The windows in the car fog up so bad I couldnt drive the car...had to pull over and wipe the windows down. But the thing is...I didnt know what the problems was...until I realized the windows werent just being fogged by the cold, ect it was a toxic mist from a heater core problem...I pulled over 2 times because I got sick...I noticed a mist coming out of the vents....so all in all I called Mitsubishi and they refuse to do anything about this.this heater core problem can lead to accidents, sickness, and othe expensive problems in the car! The fumes are extremely toxic!!! There are 1000's of complaints and blogs about this problem...I'm sure there are 100,000+ complaints abpout this problem. And Mitsubishi refuses to help or do anything about this. …
My 2002 Mitsubishi Diamante has o ring failure in the heater coil. I have read many complaints that this is common on this model and would like a recall on these vehicles due to the extreme nature of the issue. With the failure of the o rings come potential anti freeze vapors entering passenger compartment and causing physical damage to all passengers. It May also cause the car to overheat in the middle of heavy stop and go traffic and cause accidents and/or death. It May also cause the heating element to no longer work and passengers in the extreme winter climates May be susceptible to physical harm or death. Lastly, this is a rampant known issue with these vehicles and should be corrected at dealer cost. My car cost originally $30,000. …
I bought a 2002 Mitsubishi Diamante ls 10/3/07. He had 53,000 miles on it. It now has about 75,000 miles. My problem is the same as hundreds of owner of this car. Heater core issues. I recently had the heater core gaskets replaced as I was told that the heater core was OK, still had to pay for labor. It is now leaking again. This is a very common problem and seems that mitsubushi is unwilling to do anything about this. The heater core is right above the computer that runs the car. When the heater core goes bad, its leaks on the computer. What kind of sense does that make? My engine light is constantly on and I have seen the tcl light come on as well. I have searched the internet and all 3 of these problems are very common. I want to know if there is anything that can be done about this or if mitsubushi has addressed the problem and I am not aware of. …
Our 2002 mitsubishis Diamante vr-x has been misting from the heater core for a few years. The problem is bad gaskets (o-rings) that join the heater core with the lines for the heater hoses. The heater core is installed right over the PCM unit. If it leaks badly enough, the PCM and transmission relay will be destroyed. It (heater core) failed shortly after the warranty expired and when we went to Mitsubishi dealer, they refused to fix it. They quoted us $1400.00 for repairs. On the internet, there are hundreds of complaints for the same problem, but no one has gotten any satisfaction from Mitsubishi. I put some radiator stop-leak in and this seemed to help somewhat, but it is starting to mist again with anti-freeze in the passenger compartment. This is a toxin and is dangerous to inhale and will jeopardize my family's health.
At about 70,000 miles I started to see a very fine mist-like smoke coming from the dash while driving. There were no warning lamps illuminated on the dash. So after the temp gauge started to go up and I could also smell anti-freeze. I checked the radiator area and could find no leak but when I checked the coolant it was low. I topped off the coolant and a couple of months later it did the same thing. I then added stop-leak and the coolant level seems to be staying but I can still smell the anti-freeze and the windows fog up. I understand there is an issue with gaskets on the heater core. I am worried the coolant leaked into my vehicle in the area of the ECM. To me, this is a serious safety issue and Mitsubishi should be correcting this problem because it is very common from what I have read on-line.
I purchased a used 2002 Mitsubishi Diamante in August 2005. The car had 45,000 miles on it. In October when I started to use the heater I could smell an unusual smell inside the car. In January of 2006 my brother rode in the car and told me the smell was anti-freeze. I went on the internet and instantly found out that this model car has a problem with the heater core o-rings failing. The smell in the car got real bad real quick and I had to have the leaking o-rings repaired. I would get sick from the smell and had no choice but to have it fixed. I brought the car to a Mitsubishi dealer and had the repair done for $650.the car had 48,000 miles on it when the repair was made. That is alot of money for problem that Mitsubishi should have corrected.
The heater core of the 2002 Mitsubishi Diamante needs to be recalled and/or redesigned by Mitsubishi. As it is, just about every single post I see online about this car has the exact same problem. The heater is positioned directly above the car's computer , or ECU , and therefore causing problems with the engine, transmission, suspension, etc.. The entire 80-page thread linked below is almost completely about this issue : http://www.carsurvey.org/viewcomments_review_76426.html there are many others like it. The issue is mentioned in technical service bulletins by Mitsubishi but is not recalled. People are buying this car used and having to replace the heater core (around $1200 repair).
Engine complaints in other Diamante years
Frequently asked questions
How common are engine problems on the 2002 Mitsubishi Diamante?
NHTSA has 38 complaints about the engine & cooling of the 2002 Mitsubishi Diamante, 31% of the model year's 123 complaints. The component named most often is cooling system (16 mentions).
Is there a recall for 2002 Mitsubishi Diamante engine problems?
No. NHTSA lists no engine & cooling recall for the 2002 Mitsubishi Diamante, though it has 3 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2002 Mitsubishi Diamante engine problems start?
Half of the complaints with a recorded mileage happened before about 70,000 miles, and 3% before 25,000 miles.
Is it dangerous?
Owners linked 1 crash, 0 fires and 5 injuries to engine & cooling problems on this model year. If you notice symptoms, have the car checked before driving further.
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.