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1998 Chevy 3500 check engine light

I have a 1998 chevy 3500 2wd pickup with a 454 engine. The check engine light is on. I have had the codes read and they were for a MAF and MAP sensors. I have replaced both. The check engine light is still on saying that I have a bad MAF sensor. I replaced it again. The check engine light still is on. What else should I look at to fix this problem??

A vacuum leak is a likely cause.

Are you sure the circuits are ok to those sensors? It would be helpful to us here if you provided the codes you are seeing to us.

Did have the code cleared after you replace the sensors?

Provide the actual, specific codes, and stop replacing parts in response to codes. Those codes don’t tell you that parts are bad. They can’t.

There is way, way more involved in diagnosing a problem than reading the codes and replacing whatever parts are mentioned in the generic definition of the codes. I think Rod Knox is definitely on the right track by suggesting looking for a vacuum leak because a vacuum leak can cause codes to be set which are relevant to either the MAP sensor or the MAF sensor. Reading the codes and replacing whatever parts are mentioned in the generic definitions of said codes is just an expensive way to not fix anything.

“Reading the codes and replacing whatever parts are mentioned…is just an expensive way to not fix anything.”

So true. But a money generator for the ‘repair business’ for sure.

Yoda; A code reader will narrow the possibilities down but it will not identify the cause of a problem. A step up from the code readers is a basic scanner that can interface and give live data. The 98 model is OBD II and a scanner for those is somewhat reasonable. Probably less than the cost of 1 diagnostic session at even an independent shop. If you get your hands on such a scanner the gear heads here might give you all the help you need to get to the bottom of your problem. I feel certain it will be much cheaper than throwing parts at the problem. With only a code reader you have no way of knowing if the new part you install is any better than the part you took off.

I have had the codes reset, I have checked for vacuum leaks none of these things is the problem. The code is a 101 or 102 if that helps you any. I had the codes erased after I replaced the MAF and the MAP. I have checked if I am getting voltage to the MAF, which I am. If you erase the code it comes right back on immediately without even starting the truck.

If I have a live scan done while the engine is running I get responses from everything but the MAF sensor.

And that is with all three MAF that have been on the truck

On second thought, Yoda. Someone here in a recent thread mentioned a software system and a link up for a lap top. Such a system was thousands of dollars a few years ago but watch here as I feel sure the guilty party will show up and it seems they had just what you need for a pittance… So to speak.

Sounds pretty clear to me that you have a wiring issue. If you checked a wiring diagram I wouldn’t be surprised if the MAF & MAP shared a ground circuit that is having intermittent issues.

Read the codes and post the exact code numbers. Also note that the code descriptions probably refer to a problem in the circuit .

After that you probably go to work with a multimeter & wiring diagram. A scantool would also be handy. Rod Knox might be talking about one of the various laptop based devices - a patch cord from USB to OBDII port. There are multiple softwares that make them work. The cheapest one is free (OBDWiz). They’re handy and not very expensive. But they do tend to be limited in what they can do unless you start tossing lots of money on software. I spent $100 on one & it does the basics for real time sensor info.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

p101 and p102 are the codes just like I stated in a previous post

Well, you also left a bunch of ambiguity because you said you replaced parts and cleared codes and said “the code” comes back and talked only about the MAF. Yet you started out talking about both MAP & MAF. So let’s not imply that whatever you said previously was crystal clear.

So do both codes come back or what? I was after what codes are currently showing - if you read them right now. If - right now - you have P0101 and P0102 AND a scantool is showing no response from the MAF - then you do, almost certainly, have a wiring problem. You said the MAF is receiving voltage (probably 4.5V?) - but is it sending any back out that is actually reaching the PCM?

As I have stated, if you would actually read everything I say, I have checked the wiring, the vacuum, replaced the MAP and the MAF, had the codes reset, had the codes reran found out it was still saying the MAF was bad, re replaced the MAF, checked the voltage in and out of the MAF and to the ECM which read 5volts in all locations, had the engine scanned while it was running getting readings from every sensor but the MAF, and the check engine light is still on. I just don’t know where else to look for the problem. I have been around vehicles my entire life either on the auto parts side or the fixing side so I do know what I am talking about. I have just never run into this kind of a problem before. Usually you can fix the problem by replacing the part or checking everything else that has to do with the codes that are being read. After doing all of that, I still have a problem and was just seeing if anyone had a new avenue to look down, but so far everyone has only asked for the codes which I have stated twice. If my problem had anything to do with the codes it would be fixed by now.

A restricted exhaust, vacuum leak, a leak in the pipe from the throttle to the MAF, a broken or disconnected crankcase vent, and any of a number of possible vacuum leaks that are totally hidden from view can cause the codes. Take it to a good shop.

I don’t know whether to wade into this or not but I might ask how you checked the vacuum.

I read everything you said.

When you say it you don’t say much. If you’ve been around cars all that much then you should know how it gets when it comes to problems like this it gets down to really nitty gritty specifics - small things overlooked, test methods, etc.

For instance: “I have checked the wiring” That’s the first time you said that and I don’t even know what you mean by saying it. You said earlier the MAF has voltage. Are we to presume that’s what you mean? You put an actual voltmeter on it? Ok great - the MAF gets voltage. Does it send any back?

So once again - I read everything you said - you just don’t say much.

Good luck.