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Isuzu Rodeo Coolant/Sensor/Engine Light Issues


I have an Isuzu Rodeo 2002 (130,000 miles, owned since 2007, manual) with the engine light on stating that there is an issue with the coolant (I do not know the exact wording), but the mechanic stated the sensor is sending a reading to the computer and then more gas is sent to the gas when it’s not needed. He thinks it is possibly a computer issue which, of course, I do not want to hear. :slight_smile:

He also mentioned the heater core and possibly needing a new sensor but is hesitant to put another one in since the latter is still so new. My boyfriend mentioned possibly needing a radiator flush or that the radiator has a leak that may not be reflected in the coolant tank. My coolant levels are good and new coolant was put in about a month ago. There was a leak at that time in the hose that attached to the radiator which was fixed. I had a new head gasket and temperature sensor replaced in the summer of 2012.

Also, the temperature gauge in the car reads differently for the past two months than it use to. It use to stay a two notches to the left of the middle/normal mark. Now it stays about halfway or a bit less than that between the cold and middle mark when it has been driven 15 minutes or more. It also seems the heat runs cooler than usual and it also takes longer for the heat to warm up, usually just a bit past lukewarm after 15 minutes. (The mechanic had it for a few hours a few weeks ago and said the heat ran at the temperature it should–he used some sort of thermometer–and said the release or flap was moving appropriately–I believe this was on the sensor, right?) If I am at idle, the temp gauge will move up to about two notches to the left of the middle, its usual place in the past per above. Once I start driving, it will again drop down to halfway or a bit less between the C and the middle per above.

Also twice (now three times–see post below from 01/12/13) in the past month, the car has had trouble starting (I crank it, it chugs a bit like it wants to start and then dies again, or won’t start at all but the lights are on but then will catch on the third or fourth try and then runs fine after that) and then the engine light will go out and will stay off for about four or five days but then comes back on again. The fan works fine in the car. Today, it died when I was in idle, and again, it took me about four tries to get it to start with the engine either puttering a bit (I actually gave it a bit of gas as I was in a panic) or would wind like it was trying to start (again lights came on). It finally started on the fourth try and ran fine to get me home (engine light stayed on).

This is my only car and I have to be self-sufficient, so I am seeking the community’s guidance. I plan on taking it into the mechanic’s again tomorrow and letting them check it. Anything else plus what is mentioned above that you can think of would be great! Many thanks in advance for your time!

You’re going to need to get the exact code - it will look like “P1234” - and post it.

It just sounds to me like you need a new thermostat - and probably a new mechanic.

Your thermostat could be stuck slightly open, not an unusual thing for a 12 year old car, and would explain why the dash temp gauge is reading lower than normal during driving and the heater isn’t quite as hot, but that wouldn’t usually cause hard starting. You may also have an add’l problem that the coolant temp sensor used by the ECM to determine fuel/air mixture is also not working. That could explain the hard starting. Some cars have three coolant temp sensors, one for the dash gauge, one to turn on the radiator fan, and one for the ECM. Newer cars often have just one, and the ECM uses it to turn on the radiator fan and display the temp on the dashboard. Ask your mechanic the coolant temp sensor line up on your car. 3, 2, or 1?

In any event it is easy to bench-test coolant temp sensors, maybe ask your mechanic to do that with the existing one that is suspect, rather than just replacing it. It is usually just a matter of measuring the resistance at two temperatures.

There are other things that could be causing these symptoms of course. As mentioned above the first place to start is the car’s own diagnostic software. It is provided by the manufacturer to help diagnose this type of problem. Sometimes replacing parts works, but often you run out of money before you find the problem.

I will get the actual code and reading tomorrow from them and post it. II will also print off your comment, George, and take that with me. I think he did a test of the coolant temp sensors and said that the reading was accurate. He mentioned something about 130 degrees. Is that possible? The garage is great, and I’ve been going to them for a long time. They have been checking this issue in various ways for the past 1-1/2 months and haven’t charged me for it. Again, the hard starting and the dying while slowing down to a stoplight has only happened twice (one for each) during this time. Another question: Could someone with the appropriate equipment, etc., change the coolant temperature sensor and/or the thermostat themselves? I know an out-of-work mechanic who could maybe do it and could use the money, but is this something he can do from his home is the question. Thank so much for the info!

The coolant temperature sending unit often lives in the thermostat housing with (you guessed it) the thermostat. Both are usually super easy to get to (where the top radiator hose enters the engine), and you can pop them off with a socket wrench, replace them, and get it all back together in a few minutes. Draining and refilling the coolant takes longer than swapping the parts. Easy job for your unemployed mechanic friend (or yourself!).

If the coolant temp sensor is reading low all the time, the computer will think the engine is cold and enrich the fuel mixture–this will give you lousy mileage and can leave carbon deposits in the engine. It can cause harm over time. If the thermostat is bad then the car never warms up all the way–uncomfortable for you in the winter, poor gas mileage again, and over time this will hurt your engine too.

As others have said, please get the exact code read and post it here. I think Autozone will do it for free. Does the temp gauge on the dash indicate lower than normal? Are you getting a decent amount of heat coming out of the vents?

I was a bit under the weather for two days and then traveled out of town for the weekend. I plan on taking the car in tomorrow and will get the exact code. I’m taking notes from here and will take those with me. :slight_smile: A few more notes to add however: The car died on me again Friday night, the second time in a few weeks. It seems to happen when the engine is cold or at least after having sat for a few hours on a cold day and happens within about a mile from my house (meaning it hasn’t had time to warm very much from starting). I will start to decelerate as I’m coming to a stoplight, and feel a bit of puttering/mildly rough riding and then the engine will just die and the dashlights all come on (I have a new battery so not the issue). On Friday, it restarted on the second crank. The three times it has died has always been with a cold car. Dying while driving is a scary thing.

With warmer weather, the temperature gauge has been closer to the middle which has always been its norm since I have had the car. The heat worked great as well when the temperature gauge read closer to the middle (its norm).

Of note, the garage I take it to said they cannot find any reason for the check engine light reading and don’t want to replace the thermostat (saving me money) because I had a new thermostat placed about 1-1/2 years ago with a head gasket/serpentine belt repair (they actually replaced it twice as they thought it may be defective so I’ve been through several). He did mention the fuel enrichment as posted above by Oblivion, but my gas mileage so far has been fine. When they clear the engine light it will take about four days before it comes back on.

They have checked my radiator hoses and coolant levels (I keep an eye on this as well just in case the reading is wrong).

Again, I’ll post the code tomorrow evening. Question: Could this be a computer issue if nothing else seems to make sense?

Thanks again and I’ll be back.


One more thing: The mechanic said he could see the thermostat fluctuate and said that it was working. Thanks again!


I’ll go a little off topic here . . .

It’s extremely difficult to sort through your story, because you don’t have separate paragraphs


I went into edit and fixed my first post into paragraphs which hopefully helps. I used separate paragraphs in my last longer post from a few minutes ago which hopefully helps. I think in my first post I was trying to get all of the information down just out of worry and didn’t think about it. Thanks for responding!


I’ll go out on a limb here . . .

That check engine light is probably coming on due to a P0128 fault code. That code occurs when the pcm detects that the coolant temperature hasn’t risen quickly enough within a specified time frame. The causes are usually a stuck open thermostat or a low coolant level.

Since your coolant level is good (did you check if there’s enough coolant in the radiator also?) and the coolant temperature sensor is relatively new, the thermostat is most likely the cause of that P0128, assuming that is the code the mechanic retrieved

Code aside, the fact that it takes longer to get up to operating temperature also would seem to point to the thermostat.

Here’s my advice: Replace the thermostat. Since the truck is a few years old already, it wouldn’t hurt to also replace the pressure cap.

As far as the engine idling goes, the only easy advice I can give you is to clean the throttle body and the idle air control valve, if the truck has one. Strange things can happen when they’re really dirty.

Since you asked, any mechanic could do all of that stuff at his home on the weekend

BTW . . . I’ve had some bad luck with aftermarket parts not working correctly. One aftermarket thermostat actually caused my engine to run hot . . . which it didn’t do before. If you’re thinking about replacing the thermostat and the sensor again, I urge you to get genuine Isuzu parts (probably impossible, as Isuzu has left the US market) or at least very high quality parts. I advise against store brands in this case


Thank you so much for the info. I will have them check the coolant level in the radiator (my boyfriend mentioned this as well and it’s on my list) and add the pressure cap as a possibility.

I googled the idle air control valve–wow, that’s a pricey item. I’ll have them clean that and see what happens.

After-market parts: I needed a manifold in the summer and finally found one in Texas. Yes, you are right, it is a challenge to find Isuzu parts. I’m considering a new-to-me used car in the summer, but I really need this one to get me through to that point and it would be nice to have it as a second car. :slight_smile:

Again, thanks for your input. I’ll post what I have tomorrow.


As far as idle air control valves and throttle bodies go . . . the rule of thumb is generally to attempt a cleaning first

“I needed a manifold in the summer”

What manifold, and why?

What engine does the truck have?


I will definitely have them clean the above first.

Manifold related to the exhaust – that’s about as clear as I can be on that. :slight_smile: It had multiple cracks, and they would solder it; but it either wouldn’t hold or would only partially hold and I didn’t pass the emissions test for our state. The soldering (or welding?) got me through over a year before I had to replace it due to that.

I don’t know the type of engine that I have, sadly. I have the basic Rodeo (not the Sport or LS/LSE), manual, no bells or whistles. I even have crank windows and manual locks, but I like it. :slight_smile: Here is what Motor Trend says it has:

“3,165 cc 3.2 liters V 6 front engine with 93.4 mm bore, 77 mm stroke, 9.1 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder”


Okay, I am back with info. First, here is the code: P0128 - Coolant Temp.Below Spec. I had made notes from the comments above and took them into the garage. Because the engine dying was my main concern, they did a computerized engine analysis and did a “valve 3 part fuel injection service” and checked/cleaned the throttle body (db, I had put that on my list as well from your comments above) and the EGR (my understanding is that this relates to the exhaust) which apparently was slightly loose (!). So, hopefully, that will take care of that.

RE: Check Engine light - If it comes on again they will replace the coolant sensor which was replaced prior about two years ago but as stated above it is after-market because Isuzu parts are almost as rare as the dinosaur. I can live with that as it’s not that expensive and I can have my friend do that on the cheap, helping us both. I am just hoping it’s not the computer.

The head guy is still wondering if it is the computer, but I don’t even want to think about that right now.

So, we will drive it a few days and see if anything exciting happens. Any additional input is always appreciated.


It still sounds like you need a new mechanic.

  • The actual coolant temperature should be checked once the truck has been running long enough to be up to full temp and right after it is driven (the air blowing over the radiator will cool it). This is a very simple thing to do. I’m still guessing that you need a new thermostat. This is such a simple and basic thing - did they say anything about having measured the coolant temp?

  • The coolant temp sensor can also be tested. This is also very simple. Most are just resistors with resistance values that can easily be checked at different temps according to factory specs. One can also read what they are saying with a simple scantool - not even a fancy one. This also is very basic. The wiring for sensor should also be checked.

Between a loose EGR valve and bad thermostat or temp sensor, that would explain poor running and stalling.

The odds that this has something to do with a computer problem are really really really low. These things are very basic and routine and not mysteries to anyone who knows anything. So if you have more info about what they’ve checked then let it fly.


I put them on a financial cap of $200 and since the car dying was my biggest concern they focused on that. If the engine light comes on again with the coolant issue then I may have my mechanic friend check it out and will ask about doing the tests above before diving into a part replacement. The only issue with that is at $90/hour labor I can replace the coolant at $100 total. Am I viewing that correctly or missing something? Would the tests reveal if it is something more than either the thermostat (replaced two years ago as well) or coolant sensor yet still related to that whole system?



Putting a cap on it and prioritizing is perfectly reasonable. It’s really really bizarre though, given your whole picture here, that they wouldn’t have done something as simple as check the coolant temp. Ask around among people that you know to see if someone owns an infra-red thermometer. Basic ones are not fancy or expensive so it’s not an odd thing to own.

If you can lay your hands on one, the next time you’ve been driving the truck and the temp gauge is sitting down low where it’s been, just point it at the thermostat housing and see what it reads. This will not be laboratory precise but plenty good for what you need to know. Coolant temps should spend most of their time between about 190 and 230 degrees (give or take 10 degrees on either end). By about 230-240 your fan turns on and down under about 180-190 your thermostat should close - and then pop back open when it goes back over. You can sit and let it idle too and the temp will probably rise slowly because driving isn’t forcing any more air over the radiator.

If you’ve been on a reasonably long drive (figure 20 minutes, though 10 would do) and your temp is much lower than 180-190 then you need a thermostat. It really is as simple as that, and it takes 10 seconds to check. The last I knew 10 seconds didn’t cost a lot.

In any case, I don’t know this engine and some can be difficult. But 9/10 times a thermostat is very easy to change and requires only the simplest of tools. The parts might set you back all of $10 tops.

Oh, that does sound very easy. My BF has one of those gadgets and I’ll see about having that checked if it acts up again. So far, so good as the Check Engine light has remained off even after sitting on idle for 20 minutes tonight waiting on my child. We will see in a week or two. Again, thanks to you, cigroller, and everyone else who has commented. It is a learning experience and I do want to know and understand the process.

My Check Engine light came back on today. When it’s been turned off, it will often not come back on for a a few days, usually after I’ve sat at a stoplight for a few, with the engine hot or cold. Question: If it was the temperature or coolant sensor wouldn’t that message be sent to the computer and trigger the light earlier than a day or more? And I guess if it was the computer wouldn’t that be the same thing? Again, just trying to understand the process. I will see if my mechanic friend can do the tests per cigroller above and go from there.