AC & Heater complaints by model year
Which parts fail
Components named in complaints (air conditioning, heater, defroster, HVAC controls).
Mileage when the problem started
What owners report
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. …
'02 Mitsubishi Diamante; heater core failure; 2nd owner eff. 2/05; bought from same dealer that leased to 1 person; found many other owners suffering same issue on google to site: http://www.diamanteowners.com/forum/index.php?s=918c701e5465c87381ccae0aa22c20a3&showtopic=3615 I have been quoted $1200 by 2 dealers and $900 by a mechanic/independent. The dealer that leased the car to '1st owner' and sold it to me at end of lease told me that they are working on two diamantes per week for heater core replacement! Why is there no recall yet??? This leak - per brad/sale and service dealer states that if I fail to fix immediately - 10 hours of labor - radiator coolant will leak into passenger foot well/flood and the leakage goes over my computer that runs the car! 2 repairs a week is unacceptable!!! Please help!!! …
The first time my 5 year old son drove in this car, he vomitted. Everytime he rides in it he becomes nauseous. The car's windshield fogs up and a sickly sweet smell comes out of the vents. The windshield is covered in a permanent haze. We noticed these symptoms but had not given it a second thought since the car was new and had no reason to suspect major problems. The car was recently in the shop for 1 week, when we picked it up we really noticed the sweet smell and alerted the shop. After inspection the shop diagnozed it as a heater core problem, a leak that is vaporizing and condensating on the windshields. The anti-freeze fumes are noxious, and after some research we have found that Mitsubishi has been aware of the problem and has even issued 2 TSB about the problem. Mitsubishi fails to correct the problem by fixing the car. …
I have had my 2001 Mitsubishi Diamante for one year now and have always found that my front window fogged over with a film the defroster would not remove. Last weekend the 5th of February 2005 I noticed the film getting worse and the car filled with a very pungent smell of antifreeze this caused my eyes to burn and made it hard to continue driving. I took it to my dealer who said the heater core had a leak and I needed new gaskets that were $16 dollars a package and that labor would be $492 dollars for 5 hours. I was quite shocked it would cost so much considering I have well maintained my car and that I only had 41,000 miles on it. I am concerned of the health effects if I have been breathing in antifreeze for over a year now. I am also concerned that the leakage May have caused damage to my ECU because of where the leak is (right above the ECU). …
Purchased 2001 Diamante in September 2004. Had approximately 66,000 miles when purchased and approximately 73,000 miles now. At the time I purchased the car, I noticed a maple syrup smell in the interior, but I didn't know that it was an indicator of a problem so I didn't mention it, I thought it might be a cleaner that was used in the car. In December 2004, brought car to Mitsubishi dealer where car was purchased for a routine oil change and tire rotation. Was informed that strong coolant smell in interior (maple syrup smell) was from a coolant leak caused by broken o-ring which I was told by the service manager "happens in almost all diamantes". I told them that the smell was in my vehicle when I purchased it from the dealer in August and I believe they were aware of it at that time because they were able to quickly identify that same odor when I brought the car in for service. …
For several weeks it was becoming increasingly difficult for me to clear the windshield on my car and I attributed it to hot, humid weather. Coming back on the freeway one evening it suddenly became much worse and my husband and I tried many different combinations of cool/warm/fresh air to be able to see out of the window, but it never fully cleared. It was dangerous to drive under those conditions, but we made it home. There was a whitish film beginning to form on the window, visible in daylight. What was in the fumes that formed the film I am afraid to imagine. Several days later as I was driving my son to school we both noticed a white, cloudy smoke coming from the vents directly in front of us. We kept the windows down to avoid breathing in the fumes. The next day I took my car to the dealership and was told the gaskets adjacent to the heater core had failed. …
For over 2 years now I have had problems with an odor in my 2000 diamanti and the defogger never seemed to work on the windows. A couple of weeks ago I saw something leak onto the passenger side rug but didn't' t guess that this could have something to do with the heater core. Upon taking it to my dealer I was told this was hole in the heater core that had to be fixed immediately because it was dangerous and hazardous to my health to breath the fumes that were coming out of the core. The cost would be approximately $1200. I noticed I often had headaches when I drove long distances but was very concerned when my grandchild became very car sick (which had never happened before) upon riding in my car. I still didn't associate the heater with our problems. I think this is very dangerous and something should be recalled on these. …
Frequently asked questions
Which Mitsubishi Diamante years have ac & heater problems?
By NHTSA complaints, the 2002 (69), 2001 (55), 2003 (27), 2000 (24) and 1998 (14) model years. AC & Heater complaints make up 56% of all complaints for the 2002.
Is there a recall for Mitsubishi Diamante ac & heater problems?
No. NHTSA lists no a/c & heater recall for any Mitsubishi Diamante model year. A widespread problem may still be covered by an extended warranty or a manufacturer service bulletin, so ask a dealer.
At what mileage do Mitsubishi Diamante ac & heater problems start?
Across all years, half of the complaints with a recorded mileage happened before about 61,000 miles; 32% happened before 50,000 miles.
What part fails most often?
Owners most often name the defroster/defogger/hvac system › heater core (179 mentions), followed by the defroster/defogger/hvac system (16).
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.