Tonight I decided to fix my horn, a project I have been talking about doing since Late November 2007; but haven't had the time to do. So I took out the center console and the information center in the dash and replaced the relay. Horns are now working! Great, while I was in there I decided to pull the bulb for the MIL light suspecting that it had burned out. Lately the car has been running irratic on startup; I suspected it might need a Coolant Temp Sensor, but I didn't see a MIL light. Got in the information center and found the bulb was smashed. Very interesting. Anyway, hooked the bulb back up and of course the car had codes... many of them.

Code 15: Coolant Temperature Sensor - signal voltage high
Code 22: Throttle Position Sensor - signal voltage low during engine idle
Code 33: Mass Air Flow Sensor - signal voltage or frequency is high during engine idle
Code 34: Mass Air Flow Sensor - signal voltage or frequency is low during cruise
Code 36: Mass Air Flow Burnoff Circuit problem OR Transmission Shift Problem - electronically controlled shift problem

What a list. I can tell that the car needs a coolant temp sensor so that will be replaced first.

What should I tackle next and how should I go about doing it? Also, are these codes stored permanately until they are cleared or do they get erased after many miles of driving like OBDII? If not, I might have triggered the MAF codes a year ago and I should probably clear them and wait for a MIL light.

Oh, I also purchased a year of Alldata... $25 worth every cent.

Dan

Dan, you need to figure out why youre getting these DTCs before you replace anything mate, you cant just say the CTS code means the sensor is rooted, cause it doesnt. It could just as easily be a wiring issue or something else related. I dont know how you can tell it needs a new sensor, i assume youve tested it properly or you can see its physically damaged. DTC 15 on an 89 is Coolant sensor circuit low, not high, according to the info i have here

DTC 22 should be a simple fix by adjusting your TPS to correct specs.

DTC 36 has nothing whatso ever to do with the transmission, your Corvette doesnt have an electronic auto trans.

Disconnect the battery for a while and that will clear the DTCs, then see what comes back after you drive it next. You cant rely on anything listed there if you dont know how long ago the code was first logged.

I dont know what Alldata is, but if that is where this info come from (especially the DTC definitions) i wouldnt trust it as far as i could throw it.

Casey has some great advice Dan, I'll toss out a couple of other things to consider. First of all if you did that work in the dash without disconnecting the battery you took a huge risk, always disconnect the negative cable with the key in the off position before such work.
As Case indicated the codes could be old or even meaningless so a good first step before replacing anything would be to disconnect that battery now
and clear the DTC's.

Drive the car to see if the MIL illuminates again then check for codes.
If codes do return trouble shoot them using the flow charts in the FSM, if multiple codes are indeed present, trouble shoot and correct starting with the lowest numbered code. After each DTC repair clear the codes, then drive to see if the others return before moving to the next code.

For the record Casey, Alldata is a diagnostic information service available by subscription, it is highly regarded by independent garages since it provides data that is normally difficult to access, dealers however have much better technical resources and know that such aftermarket information can be flawed, incomplete or outdated. That said, Alldata is way better than nothing.

No worries mate, ive never heard of it. If there was ever any flaw in it, id be reluctant to trust it. I generally swear by the genuine manual, as the info given in this reflects on the company's reputation, and i have reasonable confidence they wont want to give their name a bum steer.

While you know I share your high regard for the FSM mate, don't ever get too comfortable using it.
The technical resources available to dealers that I mentioned in the previous post are updated often and frequently include corrections to the FSM. Such corrections and service bulletins are the information Alldata attempts to provide. Not always perfect, but better than a FSM purchased once and never updated at all.
Of course the best defense against getting burned is a good solid understanding of how the systems work which I know you have. Such knowledge will often set off a red flag before blindly following incorrect procedures

Too true mate

I trust my instincts before anything, and its very rare they let me down. The fact my Corvette very rarely ever gives me any trouble these days is almost proof of that.

To reiterate a couple of points. The code designation indicates the circuit that an out of parameter reading occurred on. It says nothing about the cause of that irregular reading. A code indicating the EGR is seldom caused by a defective EGR valve. That is why I keep saying, "Don't shoot the messenger". The FSM is the best source, I am aware of, to obtain trouble shooting charts for each of the different trouble codes. A proper sequence of checks and tests can proper diagnose and eliminate, or at least reduce, the number unneeded parts, expense, and labor involved in making repairs.

The FSM is a DIY Corvette owners best tool. It isn't without the occasional mistake, and it doesn't get updated, but unlike a Chiltons or a Haynes, it covers only your year car and it come from the maker of your car. The two manuals aren't without some help, but they are seriously lacking where we really need help, diagnosis. I have no experience with AllData, but I can't have too much faith in any help you get at Auto Zone.

RACE ON!!!

Thanks for the input guys,

The symptoms I am experiencing point me directly to the coolant temp sensor: hard start, irratic idle till closed loop, the fan is running for the moment the engine starts, of course i will use the specifications I have to properly check the sensor with my DVOM, but I was just wondering why there were so many MAF codes, and I was wondering if the TPS codes were being thrown as a result of the MAF codes. In any event, I will remove the battery cable for an extended period of time and then see what happens after I check and replace the coolant temp sensor. Thanks for the advice,


Dan

As CFI said and to elaborate on his points, you need to establish which codes are current and relative. Then look up each and every one of those codes in the FSM or other reputable source. Often when doing so it'll ask you if any other specific codes are present with the code you're referencing. Pay attention to this and read thoroughly through all relative info before beginning your step by step diagnostic process. Don't skip any steps and fully understand the procedures you're going through to methodically eliminate problems one by one. And remember as CFI-EFI has already said, any code does not automatically mean that the sensor in that circuit is at fault. The connector in the plug for any given component could be not making good contact, a wire could have excessive resistance, be open or grounded, a critical ground could be compromised and etc. Only a methodical approach can have any hope of insuring a conclusive and satisfactory resolution to these electronic gremlins that plague us all now and then. Also, this process will educate you, increase your understanding and aid you in the future when other problems occur.

Thanks for the advice guys. Upon inspection of the coolant temperature sensor, I found that it somehow got smashed . The pigtail connector was hanging and the sensor itself had no pins. I removed the broken sensor and replaced it. Checked the pigtail.. all looks well. I connected it up and cleared the codes. Hopefully those other codes are from a while ago. So far, after a short ride, no new codes, no MIL. If they pop back up I will print up a flow chart and start diag. Thanks for the tips,

Dan