Desperately in need of advice guys. This has been an ongoing issue for years and it seems to be getting worse. My big '97 Sport pops the P0125 code. It started this about 5-6 years ago. Back then it'd happen once or twice a year and seemed to be strictly related to how well the coolant system was bled. Now it happens up to 2 times a day.

The dealership is stumped. Four different techs have worked on this over the years as well as myself. We've been through the entire list on Mitsu's troubleshooting database several times including replacing the ECU. ECT, O2 sensors, etc. have been replaced multiple times.

It is NOT engine related as this problem reared it's ugly head years before I replaced the 3.0L with the 3.5L last spring. The engine replacement had no effect at all on frequency or the conditions under when it triggers.

I've ruled out exhaust leaks or anything related - again - as I've replaced the exhaust three times since '98 and there's never been a change.

Both O2 sensors have been replaced a dozen times. I've used the dealership sensors, Nippon and Bosch. No change.

The problem is MUCH worse when as the ambient temperature goes up. In the winter it hardly does it at all - if at all. Now that it's spring and the temps are back in the 60-70s its back up to once every couple days or once/twice a day.

We just went through the top end looking for vacuum leaks last week and found nothing.

No other codes trigger - ever. Gas mileage is back up to 17.5 average and there's no driveability issues. Mileage is a tad on the low side for DD usage, but not abnormally so given how crappy traffic has been, the wind and adding 8 miles of steep up hill drive to my new place.

This is a real PITA as I've got an emissions test coming up in June and any trouble codes - pending or otherwise - are an automatic failure.

Need suggestions guys. Everyone here is flat out of ideas. <img src="/forums/images/graemlins/frown.gif" alt="" />

Edward
www.4x4extremesports.com

What does the P0125 code supposedly indicate? <img src="/forums/images/graemlins/confused.gif" alt="" />

Assume you've replaced thermostat, right? With genuine Mitsu one?

Live data tests to see what the ECU is actually seeing from the various sensors?

Overactive cooling fan chilling things off just a few degrees too much?

Voltage drop tests on the wiring between sensors and ECU?

Sorry, the following should have gone in my original post. Drives me nuts when others do this and then I do it. Sigh. <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

1997 LS Montero Sport 3.L 5-speed manual w/ 2002 3.5L engine conversion. Federal emissions. This is my SAS'd Sport, BTW, not my little (stock) '97.


"P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control" is the official designation.

According to the techs, it means the O2 sensors heat rise time is too long. In English, the forward O2 sensor isn't heating up fast enough.

Exactly how that could be is a mystery.

The code will trigger like clock work at EXACTLY the same location on the way into work if it's going to trigger at all that day. If I reset the ECU, occasionally it'll trigger again latter in the day but that's apparently random.

The distance is about three miles - about 8 minutes driving at 15-55 Mph. It's gotten bad enough I can tell the mile marker it'll trigger at. <img src="/forums/images/graemlins/frown.gif" alt="" /> <img src="/forums/images/graemlins/frown.gif" alt="" />

The senior tech says that the early '97-'98 Montero Sport had a problem with mis-routed O2 wiring that would cause a short eventually in the body and sometimes cause this problem. That's been checked. They tore the entire passenger side apart earlier this year. Nothing.

Apparently I was 'lucky' and ended up with the "mis-routed fuel pump wire that will burn your car to the ground" issue instead. <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> THIS problem was fixed back in '02-'03, several years before the P0125 started up.

It does it with the factory radiator and both of my after market radiators and with or without the electric fans.




A dozen thermostats. KIM, that the entire engine was replaced last May/June with a 3.5L. Everything external was replaced prior to the install, except the water pump and two tensioners, alternator, A/C and P/S. The tensioners and alternator have since been replaced. So, sensors, thermostat, hoses, IAC, MAP, etc. - all OEM parts with less than a few K miles on them. This problem isn't new, it's been going on long before last year.

I only use actual Mitsu parts, with the exception of the O2 sensors which are currently Nippon - which is Mitsu's part - but not from Mitsubishi direct. I just ordered two replacement O2 sensors from the dealership. They'll be in next week, but I'm not holding my breath. <img src="/forums/images/graemlins/frown.gif" alt="" />

As far as I can see from monitoring everything is fine. I've run O2 tests and so has the dealership - a bunch of times and everything says there's no problem. Nothing else stands out when monitoring.

The 'closed loop' thing is weird 'cause it never changes when this happens. Its in closed loop and stays in closed loop.

The electric fans most of the time aren't even on when this happens. The engine is up to operating temperature well before the code appears AND its WORSE when it's 60+ degrees out and almost never happens in the winter when its below freezing.

I haven't done a voltage drop test. I don't know if the techs have or not. I don't think that's it as I've got months of logging accumulated by now and have seen no problems with the ECT. I've verified that the temp judged by the ECT is actually the temperature, so it's not off, either. The ECT itself has been replaced 4-5 times and I've cleaned the contacts several times.

Edward

I wonder what would happen if you insullated the t'stat housing and sensor...

I would also log the voltage to the ohtwo sensor heaters. I fouund the following:

"P0125 set if after the engine is warmed up, A/F Sensor Output* does not change when
conditions (a), (b), (c), and (d) continue for at least 1.5 min.:
a. Engine speed: 1,500 rpm or more
b. Vehicle speed: 25 û 62 mph (40 û100 km/h)
c. Throttle valve is not fully closed
d. 140 sec. or more after starting engine
*Output values changes inside ECM only


After checking around further, those are the conditions that factor into the fault. So the code haas nothing to do with the coolant temperature sensor gating out the closed loop operation, but instead is related to the O2 sensor readings..

I'll check into the O2 sensor next."

Yep, that's what the techs have been telling me for years.

Not sure, but I don't think that would do anything. This also happens after the vehicle has been on the road for hours in 80-90 degree temps. As you pointed out, coolant temp has nothing to actually do with this - at least in this case.

The techs did log the voltages, etc. on the sensor heaters and sensors themselves. They brought that up a few months ago - at the same time as the short issue on the Sports - and nothing came up. Everything was well within spec and they drove it around for quite a while. Of course, the code wouldn't trigger.

That defines an O2 sensor - specifically the forward sensor on the '90s FED Sports - issue. I've been through that from the service manuals. It meets the a-d criteria, but I'm certain the sensor output changes. I can log the output from both sensors and they're definitely constantly changing when it triggers. I've even got logs of everything through a trigger.

The other thing that doesn't sit right is the timing of the happening. It takes me about 8 minutes to get from cold start-up to where it triggers. This happens consistently. Pretty close to the same amount of time/distance when leaving the office.

Warm up time is considerably different between leaving my condo and leaving my house, yet the distance/time to trigger has stayed the same.

Its like the ECU is expecting and event within n time, irrespective of conditions and if the event doesn't happen it triggers the code.

Why this code? There are LOTS of things that fit that bill in the ECU, but none that trigger THIS - and ONLY this - particular code. <img src="/forums/images/graemlins/confused.gif" alt="" />

Just thinking out loud ... When I leave from my condo it's entirely up hill against the wind to the trigger point. When I leave my house it's entirely coasting with tail wind to the trigger point. Average speed over the period is virtually identical. I have almost exactly the same 30 MPH distance and 55 MPH distance to trigger for both. So, condo is much more throttle and house is very lite throttle. Those two scenarios drastically affect A/F ratio. Yet the trigger time/distance is almost identical.

From a mechanical/electrical standpoint - the problem occurs on two completely different engines. The only common parts are the water pump, TB and MAF. Everything electrical on 3.5L either came with the 3.5L or is new Mitsu parts.

I replaced the O2 sensors at engine install time. Exhaust stayed the same except mods to the down pipes to fit them to the 3.5L. No leaks, I checked. Down pipes have the equivalent insulation to the stock set. Forward sensor position in the pipe has not changed. The rear has by about 6-8" (rearward) but that happened long after the problem cropped up.

ECU has been replaced. I have another one on order which should be here in a couple days as well as two Mitsu OEM O2 sensors.

Sigh. Like I said. Stumped.

Edward

I would try one more cheap shot in the dark. Try the fix for the code that says that the rear ohtwo sensor is bad - install a spark plug antifouler fitting between the bung and the rear sensor. It's cheap and pretty easy to install.

Otherwise, the new ecu may fix it. From reading the quote and comments, and your posts, it appears that you have changed all the related parts at least once. The only thing that seems to be possible is that the ecu is not logging the change in the ohtwo sensor readings after a-d conditions are met.

Good luck. This one is a head scratcher.

edit: I found the following:

"No.: TSB-07-13-002

DATE: January, 2007

MODEL: 2001-04 Montero

SUBJECT:
PCM REPROGRAMMING FOR DTC P0125

This TSB supercedes TSB-04-13-011, issued October, 2004 to revise the required MUT-III cable and to add the 12-13 pin adapter for 2002-04 models. Revised information is indicated by [<].

PURPOSE

Incorrect PCM software parameters may cause Diagnostic Trouble Code P0125 to set when the vehicle is driven in cold ambient temperatures. To eliminate this condition, reprogram the PCM as described in this bulletin.

AFFECTED VEHICLES
2001-04 Montero "

I have two O2 sensors showing up at the dealership sometime next week. I'll try those first. At that point there won't be anything that isn't a factory Mitsu part on the electrical side of things. See what that does.

If that doesn't do anything, I'll drop in the new ECU. I REALLY don't think this is going to do anything, but ....

If it's still coming up I'll try that. I don't know what it's supposed to do, but at this point I'll try just about anything. <img src="/forums/images/graemlins/frown.gif" alt="" />



With the exception of the ECU, three-four times. Sigh.



Yea, you're not kidding. An actual electrical problem SHOULD actually cause other issues besides this. In fact, I should have a LOT of issues if the ECT circuit is faulty.

Yep. Seen that one some time ago. Problem is, mine does it when it's warm out.

So, I got my panties in a bunch last week and decided to stop resetting the ECU when the code popped. It takes SOOOOOOO long for the ECU to relearn that with this code coming up so often the ECU is almost always half jacked up. Since the driveability and gas miliage isn't affected, I decided to just leave it on.

Anyway, the code apparently will clear on its own. Or, at least the dash light will go off. Dash light came on, went off, then came back on a day latter late last week and today it cleared again on its own. No apparent rhyme or reason. I'll see how long it stays off this time.

Edward