1st Oct 2009, 14:26

Purchased a 2002 Diamante LS in June with 86K on it. Here I am in October with 94k on it and it's time to replace the heater core. I haven't taken it to the shop yet, but everybody is explaining my problems exactly. Screw Mitsubishi, recall this crap ass vehicle. $1400 to replace some crap piece of machinery you chose to use to cut down costs? What kind of company are you running? I'm going back to American.

16th Dec 2009, 00:35

I, like many here, am having issues with a leaky heater core. Fortunately for me, my TCU is dry. Can't say the same for the A/T relay. I unplugged it and it was SOAKED with coolant. Before I go to the dealer, is there a site online that sells the A/T relays?

Send me an email @ mofoe2001@yahoo.com


10th Sep 2010, 18:41

I am in the EXACT same situation as many of you. I was having fairly sporadic problems with my transmission acting funny, but if I turned the car off and then back on, it would usually fix itself. Now, it is permanently screwed up. Can anybody tell me how to find this dang A/T Relay? Or give me a part number... Any help would be greatly appreciated. email: tinz1722@aol.com

13th Sep 2010, 06:01

Well I found this website while researching a suspected transmission problem.

I have also had to bypass the heater core on my 2002 Diamante. Also had to replace the antenna motor. The door seals on the rear doors are a joke. I can hear the wind coming in around 70 MPH.

There is 73,000 on it. I bought it second hand and was able to put 30K miles on it before all these problems occurred.

The transmission problem is as follows. The service engine soon light came on. The car jerks when put in reverse. It feels like the trans is slipping in gear. I have only driven it around the block since I got the light yesterday. I am taking it to get the code read tomorrow.

These cars are really pieces of junk. When they run well they are great, but they cost more to maintain than a 5 series BMW. If my trans is bad I am going to scrap the car. I can get a used Honda for 5k and avoid all this crap.

No wonder they quit building these things.

18th Sep 2010, 23:12

I am having the same problem. My service engine soon light came on, and my transmission is acting funny. My transmission was acting funny before the light came on. Any help would be great.

22nd Sep 2010, 19:18

The transmission just went on my 2002 Diamante. Do not drive it, as I was told that the the manufacturer actually issued a revised part - no recall - because when the piece cracks, it mangles the rest of the transmission. Hopefully, you can catch it before you end up like I did - $$$$$.

1st Oct 2010, 12:09

It seems like lots of transmission problems here. Also the heater core leaks are legendary. If you have a leaking heater core and live in a warm climate, I would recommend bypassing the heater core permanently. If you catch it early enough, the relays will remain dry and you could avoid these expensive problems.

Of course if you live in a cold place, then this is not practical. I have read about the radiator stop leak fix, and I would probably try it if I had to. Just follow the instructions exactly, or you could plug up some very important water passages in the engine, and cause more damage.

If you have engine problems AND transmission problems, I would recommend calling a wrecking yard. At that point, the car is probably worth less than $1000. A wrecking yard might give you $200 or so.

The funny thing is, that these cars are really fun to drive and are very comfortable. Too bad they ruined the car with this heater core problem. Everyone here who wants the dealer to fix these problems when the car is out of warranty (which they all are by now); I agree with you. But rest assured, it will not happen.

Good luck!

4th Dec 2010, 15:02

You know, I really like this car, but I have the same 4 items you all have. The thing is I did find the Technical Service Bulletins (TSB) on three of these: Traction control light, ECM problem and the transmission problem. Funny thing is my local dealers here in SATX don't seem to want to quote the fix, skirting around and changing labor rates. Nice! Anyway here are the bulletins, hope you have more success than I did.

TSB-05-23-004 REVII - addresses the 2-3 tans shift flare and eventual trans assumed failure.

TSB-06-00-004 Reprogramming the ECU with MUT-III - basically the ECU needs an update, otherwise the transmission slips and other electrical maladies appear.

TSB02-3-002 Traction Control Light is ON - The dealer was telling you all the wrong fix - it is NOT the rear wheel sensor. It is electrical interference at the distributor. All it takes is a filter soldered in line. That does it.

On more thing - be aware of a recall that can really kill. Look up #02V100000 regarding the engine wiring harness. Apparently our friends designed the harness too close to the exhaust manifold, and if it melts, you could have all sorts of issues.


2nd Jan 2011, 23:47

My 02 Diamante started acting strange as I was driving. The RPMs were going up and down. I pulled off to the side of the road and turned the engine off. Started it back up to put it in drive then reverse and it wouldn't do anything. It started to smell like burnt rubber. What could it be?

4th Jan 2011, 10:37

Not sure about the rubber smell, but your transmission just went out just as mine did at 60K.

10th Jan 2011, 18:55

I have a 2000 Diamante Mitsubishi that is failing to provide me with heat. The heat core was replaced in 2009. When the heat dial is place at every level, the air ratio increases and just blow cold air. Oh, the air conditioning works fine.

Can anyone tell me what the problem is and where I need to go to repair the problem so I can get some heat in my car? It is cold out here. The seat warmer is working fine.

In addition, my Traction Control (TCL) just went on; should I take it to a dealer or can I fix the problem myself? The car has over 109,998 miles on the odometer.

9th Jun 2011, 06:10

2003 Diamante LS Great Auto: I'm having problems with my 2003 Mitsubishi Diamante. It's the heater core o-ring or gasket. The drive and 3rd gear are flashing. The bad O-ring is allowing moisture to hit the trans, and may effect the PCM. I hope not; the odor is anti-freeze. So it's at the dealership. We hope they use the web and get some info that will help them find the common problem.

youngelta66@gmail.com (P.S.: this is consistent after 40,000mi. Mine started at 54,000mi.)

16th Jun 2011, 21:12

I was given a 2000 Mitsubishi Diamante LS. I like the car, but it does have similar issues like all other Diamante's on this site. This car has over 250,000 miles. I've only had this car for two months.

When I first was given the car, it wasn't working. It was found to be something wrong with the throttle and the "solenoid". Both were replaced. Then something was wrong with the valve cover, and it took a long time to replace. Finding one was difficult, as these cars are very hard to find. And now the TCL light is on.

At first it was on and off, and now it's just on. A few weeks later, the service engine light is on. The TCL and service lights are on constantly. At times, the service light would go on and off. We took the car to the shop, and the service light was reset. They figured by resetting, it would prevent it from coming back on. But it is still on. They also said resetting it would refresh and "pin point" or detect the problem.

Once they put it on the diagnostic machine, one mechanic says that it was a "faulty" TCL switch, which is triggering the service engine light. I'm like, "Really. This little switch (from inside the car) is causing the TCL light to display?" I didn't believe it.

Another mechanic also said that the catalytic converter needs to be replaced, and that something else can be triggering the service engine light, but according to the diagnostic, it's the TCL switch and catalytic converter (pre-cut). It's unclear as to what is wrong.

Is there anything else that can cause the TCL light and service engine light to come one? Is there something the mechanics should be looking for? We just found out that it won't pass smog because that service engine light is on.

These questions are directed to the person with the manual, and for any other person who may know.

I am dependent upon this vehicle, and can't afford to buy another; that's why it was given to me. I have invested time and money into getting the problem solved and fixed. I need to know what can be done before another problem starts. I don't live near any other modes of transportation. Having a car is a must!

I await your response...