Codes

[Mabolzich]

Hi Guys,
I have a red 1986 Vette. It's a strong runner, but these error codes keep poping up.

25 MAT sensor High temperature fault (EFI/TPI/SFI)

32 EGR circuit fault (EFI/TBI)

36 MAF/MAP sensor too high

41 Electronic Spark Timing

42 Electronic Spark Timing monitor error

I have to say that the engine and trans. were just rebuilt, but I was getting these codes off and on since I got the car in 2003. It'll run great for a few hundred miles with no codes, then it'll run great with the codes popin' up after 15 minutes. Can I hurt anything by driving the car and how can I get rid of these codes. This is driving me nuts!

 

[Schrade]

The 25 and 36 codes are for a signal exceeding spec range for too long. If you catch them in the act - put a multimeter on the source lead and check voltage.

I think they do NOT share a common ground, but you'll need to confirm that.

Do you have FSM? If not, you should get one off eBay, or borrow one from the local dealer. A third option is a subscription to Mitchell's online, or AllData. Get a spare hard drive, and 'save' all the info. If you ever sell the car, the data will add to the value, plus it will pay for itself first repair...

 

[Mabolzich]

Thanks, I can do that. I don't have a FSM. I do have AllData.

 

[vetteboy86]

Broken, or brittle wires. It is possible that after the engine build, if original connectors and wires were used some of this stuff broke. Perhaps it was failing before the build. I am assuming that when the motor was out the battery was unhooked, so that should have reset any existing codes.

 

[Mabolzich]

I've had this problem since I got the car in 2003. I worked the codes out and now, after the rebuild, they're back. The car runs great, starts right up, and is very smooth. I clear the codes, start it up, and 41 and 25 come on immediatly , the rest show up in a few miles. I visually checked the wires and connectors and they seem OK.

 

[vetteboy86]

My FSM says:

Code 41 cylinder select error
code 42 electronic spark timing
code 43 electronic spark control

By any chance was a custom tune done with your vehicle? Might explain code 41.

Code 42 will be thrown if the EST wire was unplugged. Usually performed when setting base timing.

Code 43 is the knock sensor circuit.

 

[Mabolzich]

:confusedWhen I picked up my car for the "tuner", it ran alright and no codes turned up on the ride home(about 41 miles). The next day all it was hard to start and would do backfire, so I advanced the timing until it stopped. Now is runs like a scalded cat, no backfires, starts on the first turn, and is throwing codes left and right.

 

[vetteboy86]

We could speculate about alot. If it was running okay from the tuner, it doesn't make sense that they screwed up the tune. I'll never say never though.

Check the wiring under the hood. The EST wire is located on the drivers side of the distributor. I would also start by checking the knock sensor wire. Follow it as far as you can. I'm not sure if it will throw this code if disconnected. I can dig some more in my FSM.

Does your cooling fan run as soon as you turn the key to on when the car is cold?

What did you advance the timing too?

 

[vetteoz]

start by checking the knock sensor wire. I'm not sure if it will throw this code if disconnected.

Sure will and engine will run like crap if it is because if ECM doesn't see knock sensor ( doesn't have to be working ; just has to be "seen" ) it won't give you spark advance over 1500rpm to prevent you blowing up motor.

 

[Schrade]

I clear the codes, start it up, and 41 and 25 come on immediatly ,.

That's a big clue...

Most codes won't light up until closed loop (unless they're already in history). If they've all been cleared, and they light back up right away, that's gonna' be easy to track down.

READ diags procedure for those 2, and see if there's a common link. Then get a wrench on (or a multimeter uh huh). You just have to do exactly as described. And there's always one part of the diags sequence that is a pain, or you don't understand, etc. Like a part with one hard-to-get-at bolt - every one has one, and the part ain't gonna' come off till it's out NOPE.

 

[Hib Halverson]

That you can clear codes then key-up and have them all reset means they are "hard" faults.

The best way to approach the problem is start by reading the Factory Service Manual discussions of each of those codes. I suggest that because, in the first post, the nomenclature used to describe the codes you have is not correct. That leads me to believe you're might be using some non-factory service data. If you don't have the FSM, you lack adequate information to fix these problems.

Wiring and connections are always the first place to look for problems. With respect to some of those codes, check the 4-pin weatherpac connector just below the distributor and make sure all the pins are free of corrosion. You may need a magnifier of some sort to see them. Also, with respect to DTC41, make sure the ECM "chip" is properly seated.

 

[Mabolzich]

I advanced the timing until it stopped backfiring. I didn't used a timing light, I just advanced it until it smoothed out, I guess about 4 degrees. With the timing where it's a the engine runs smoothly, starts on the first turn, and idles at about seven grand. I will, however, check the EST wire. I had a bad experience with the "tuner guy". He kept my car for 15 months and gave me the runaround everytime I called him. I don't want him touching my car ever again (long story). Where is the knock sensor wire?

 

[Mabolzich]

I have a FSN and I've been reading the section on codes. I Just cleared the codes, got a no code message on my OB1, started the engine, and code 41,33, and 32 come up. By the way, the fan comes on at 227 degrees. I pulled the weatherpax connecter, tach connecter, the battery connecter, and they seem fine, but I'm s little blind nowadays so I'll clean them and put a little dielectric grease on em. I'll also check the EMC. Sure wish I had smaller hands. I guess there is no quick fix. Thanks again for the help, the other discussion groups ignore these questions.

 

[Mabolzich]

It's a good thing that I have a spare Vette to drive or else I'd go nuts.:W

 

[vetteboy86]

Sure will and engine will run like crap if it is because if ECM doesn't see knock sensor ( doesn't have to be working ; just has to be "seen" ) it won't give you spark advance over 1500rpm to prevent you blowing up motor.

I got to thinking about this, and I didn't experience this. When I got my first mail order tune, everytime I would engage PE I would see knock retard. I originally thought it was something built into the coding, so I fooled around for a while and one of the things I did was disconnect the knock sensor. The car ran fine without it, and didn't pick up any knock. Right after I did this I became wise and realised that I should check fueling, timing, and load more closely. I was able to eliminate the knock through hours and hours testing and tuning.

I have no evidence to back this nor, have I looked into the ESC circuit. I'm going to investigate more.

Mabolzich, I'm at work, so what is a code 33?

 

[Mabolzich]

33 MAP sensor voltage low - pressure low/vacuum high​

33 MAF signal low - flow high (EFI/TPI/SFI)
The engine dosen.t knock, it runs great, I just get error codes.

 

[Schrade]

With all these codes, there HAS TO be at least 2 (if not MORE) that are traceable to a common fault.

Get away from the car for a couple of hours, for starters.

I really think you need to PRINT OUT diagnostic procedure for EACH code that you have. Read the BEGINNING of each diagnostic flow chart, and see if it says to look FIRST for another code (that you might have). My cash is on you WILL find a reference to another code. This is the ONLY way you're gonna' find anything too uh huh.

You say the wiring seems ok. No. Only way to confirm wiring is with a multimeter, or your tongue.

EVERY car runs like a scalded cat, or dog (or raped ape, whatever that is), with the pedal down. Doesn't matter how many codes there are. Idle quality is the only thing that tells you stuff.

Did your rebuilder do an itemized bill? Can you post it up?

 

[Mabolzich]

I feel the same way about the codes. There has to be a common thread to link the problems. When I said that the car ran well I mean that since adjusted the timing, the car starts on the first turn, idles smoothly, and I've driven it over a thousand miles without a hitch, except for the codes poping up. I've stayed away from it since Sunday and won't get back to it till Friday. As a instrument repairman I understand the psychology of not thinking about a problem for a few days. I will post the bill later today. Thanks for your concern and help.

 

[vetteboy86]

Let's not forget the car was at a tuner for 15 months? Was the tuner the same as the builder, or have any professional affiliation? What type of "chip" was put back into your ECM?

I agree with schrade 100%. Lay each code flow chart out and go over them.

 

[Mabolzich]

Tuner?

The tuner is also a builder. I'm a musician and my band played for a Michigan Corvette clubs X-mas party for several years in a row. The Vette racing team and several GM bigshots were there and we hung out. I knew that I was going to neeed to rebuild the engine sooner or later so I asked for some names. It was just my misfortune to pick the wrong guy out of the list I had. He gave me the runaround for 15 months a finally, after lots of proding and gnashing of teeth I got my car back. I found out that the machine shop that did the engine work installed the wrong crank The pistons wern't quite coming up all the way and the compression was way too low. The car ran, but not well. Apparently it was a special crank for a supercharged racer, or so I was told. The car was done after 3 months and it took him the other 12 too figure out what was wrong, and I kept getting put to the end of the line. This was my first experience with a "professional tuner". I was stupid, and I believed him. My 98 is approaching 138,000 and I'll be more careful next time. I like to believe that people are honest and I approach life that way. I've only been burned a couple of times, but this one was the best. Now I'll just follow the wires and sort out the codes, I'll get it. Thanks for the help.