Just bought a 2002 Limited with 132,000k miles on it. She was babied and well taken care of, immaculate service records and interior is almost new. Love the nimbleness combined with the size and capabilities. Honestly do not see why folks think it is a "slow and lumbering hulk of a vehicle". She gets up and goes when needed by switching over to the slapstick shifter. Either way.....

Check engine light came on one day and would not start the next.
Mechanics replaced cam position sensor and crank sensor. She starts up strong and runs strong now. However the check engine light is still on, engine coolant gauge jumps and random lights like the differential light will even come up on occasion.

Still getting "open loop" error
Oreilly Auto received p0421 "Catalyst efficiency below threshold" and the experienced tech there advised me that it was most likely the coolant thermostat. Said that when the vehicle cranks everything stays in an open loop until all of the sensors feedback properly.

However, the current the mechanic has no idea and thinks it may be the cluster. At this point I am grabbing the $20 part to try out but have heard some folks with Monteros have had this issue in the past.

Anyone with experience out there seen this before?

Thanks in advance,

 

Hi Ulfberht, congrats on your purchase. When you say "coolant gauge jumps" - what do you mean? Does it go Hot/Cold/Normal all the time when you drive, or does it occasionally goes to Hot and then returns to Normal?
Differential light (I assume it is Center Diff Lock orange light) - does it flash then go off, or does it flash and stay flashing until next engine restart?

P0421 code most likely means your catalytic converter is bad (past it's usable life). However, I would not confirm it 100% until you see the O2 sensor readings for both pre- and post- cat sensors.

I'm not sure what the "open loop" error means. I know what open loop is, but what is the "error" part of it? Do you get a specific error code for that?

 

Thanks, and thanks for the response.

The temperature gauge jumps and is erratic. It does not seem to follow a standard warm up at the light and cool down movement and flow. It will jump all the way to the red zone almost immediately when cranked. Laser thermometer shows the engine staying around 140-142°

The "old timer"(and I mean that with respect for the mans experience) at Oreilly pulled the codes:
P0421 and
P0340

Those are what I was referring to when saying "error". The code brought up known fixes for several things: the catalytic converter, O2 sensor, exhaust manifold and engine coolant temp sensor. He said since it was running smoothly and had not startup issues to go with the coolant temp sensor. Also the cheapest part to start out with. He said that it causes an "open loop" error reading which the mechanic also found. Apparently on startup the computer goes into an "open loop" where it registers responses from all of the sensors for calibration. If one fails it will throw that terminology or error code apparently?

The mechanic could not figure it out and another mechanic was telling him it may be the dash cluster and that it was a "known issue". The orange differentiate light came on once and the check engine light is erratic but stays on almost all the time.

 

Just throwing this out there - your mechanic had replaced cam position sensor already. Since you still have P0340 code, it is likely that ether sensor was not installed correctly or the connector is not fully engaged.
As far as P0420 code, that one will be set only after the vehicle goes into "closed loop". This means that all other sensors are reporting, but the values show not an expected value. I do not think your gauge or P0420 are related to the coolant sensor. It sounds like the gauge showing the typical Montero error. These clusters are know for getting temp gauge acting erratically. There are several threads on this subject on the forum. The only real way to fix it is ether 1. have dealer replace it ($$$$$) or 2. re-flow soldered contacts on the temp gauge board (doing it yourself is tedious but virtually free).

Here is one post on how to do this:
https://mitsubishiforum.com/forum/mi...unction-28833/

And here is another one dealing with the same issue:
https://mitsubishiforum.com/forum/mi...p-gauge-47609/

Last but not least: http://www.pajero.guru/how-to-fix-th...-nm-2001-1003/
Hope this helps.

 

Orrrr...If its not a safety or driveability issue...just put a piece of black tape
over the idiot light...worked for me on my 1999 Malibu...every mechanic gave me a different answer...including the Dealer... drove it like that for 7 years...and 320000 km when I traded it for a riding lawnmower..lol.