There are all sorts of error tolerances programmed into the computer for monitoring systems. If the computer set a code and turned on the light every time it saw something out of spec it would turn into the proverbial “boy cries wolf” situation. The dumb light would be going off all of the time and people would ignore them even more than they already do.
So most errors have to occur something like a certain number of times over a certain amount of time and/or over a certain number of drive cycles. The specific conditions for setting any particular code on any particular vehicle can normally be pulled from a factory service manual. The computer will also store “pending codes.” These can be read by many code readers, but haven’t yet turned on the light. It’s sort of a 3 strikes policy.
These days I often find and fix problems that should set codes before a code even gets set. My most recent included an EGR system problem and fuel injector problem, both of which caused me noticable issues but the computer wasn’t ready to call them “errors” yet. My minivan has an issue right now that should be setting a code. I’ve started trying to diagnose, but am sort of waiting (and waiting…and waiting…) for a code to help me out a little.
Anyway, you should have the codes read again, though I wouldn’t be surprised if it’s P0128 yet again. You do know that many big-box auto parts stores will read these for free right?
Then if you have the P0128 or anything else with cooling system reference, your best bet, if your BF does have an IR thermometer, is to just use it. It really is as simple as point and click and you’ll know in seconds.
That makes sense. I also did a bit of research on the code; and I gained more education about all of that. So far so good on stalling but it only happened once every few weeks or even a month so we shall see. I haven’t resolved the temp/therm/sensor thing yet; everybody has been busy and it sounds like there is no real risk short term. So far, gas mileage has been fine. It can wait a week or so. I’m just hoping the stalling has resolved.
It is normal for a CEL to come back on after being reset by the mechanic or disconnecting the battery. The car has to run a set of tests to decide if it is working or not, and that takes a certain number of miles driven and under several types of driving, stop & go, expressway, freeway, etc. The fact that the CEL came back on means there is a DTC stored, and reading that is what to do about the CEL. You might as well take advantage of the diagnostic service provided by the manufacturer, you paid for it after all.
One other thing, you mention above that the exhaust manifold is cracked. Be aware that any crack in the exhaust system upstream of an O2 sensor confuses the ECM as to how much gas should be injected, and may make the car difficult to start, idle poorly, stall, poor gas mileage, and generally fail to perform well.
The old manifold was cracked, but it was replaced this past summer 2013. I hope to tackle the code/CEL next week when life has calmed down. Seeing that CEL keeps me on my toes though I am less stressed about it now . . . until the car stalls again, that is. Thanks for the info.
Update: I finally broke down and had the coolant sensor replaced on Saturday after it died on me again while driving about six miles from my house with a cool (not cold) engine per its usual behavior. The CEL came back on the following day. Per the garage, the next step (assuming the code is the same as I haven’t been able to get that checked yet) will be to replace the throttle sensor and then the EGR (forgive me if I have those wrong–I don’t have my notes in front of me) in order of cheapest to more expensive. The last and final thing to do would be to consider replacing the computer. I talked to another Isuzu owner today, and he said his temperature gauge starting reading crazily and his speedometer stopped working which alerted him that something was wrong (this was in 2007 in his 1998 Rodeo). The issue was the computer, and it cost about $600.00 for a new one. I may have to contemplate doing that as it is still cheaper than a new car. Any input from the Car Talk Nation is again greatly appreciated!
Wordy - before anyone threw a temp sensor at it they were supposed to check the actual coolant temperature. Was that ever done? This thread is long and was a whole ago now, and I didn’t go rescan the details, but did a new thermostat ever enter this picture? One that is sticking open will give you slow warm up, a cool heater, and make you run rich all of the time.
Yep, it is a long thread – the same old problem with no resolution. I believe the prior guy who is no longer there did a temperature sensor test, noting that the flap did go up and down appropriately. It was also replaced two years ago. I also think he did a coolant temperature as he mentioned the temperature was consistent with 130 degrees and was reading correctly. He did say he had tested everything and that the next step would be to start replacing items though again he didn’t want to replace the temp sensor due to it being so new. I hope to get the code read in a day or two, but I am assuming it is the same one regarding the coolant sensor. I’ll update when I do. Thanks for taking the time.
If the coolant temp is reading 130 then you need a new thermostat. Once the truck is fully warmed up the min temp is around the neighborhood of 190. Below that the thermostat closes - if it’s working correctly.
Given that the temp sensor was checked and reading correctly it is bizarre that anyone would replace it.
Thanks for the info.