I have already read many of the posts on this problem, but before I try to hang under the dash to remove the programmer, I would like to be reasonably certain that it is the problem. I have checked fuses 1,4,18 and 43, they are good. The car is a 94 ZR1. I have another 94 C4 automatic. I have pulled the control head from that car and installed it in the ZR1 and It behaves the same. (3 dashes) and none of the buttons work. Both control heads work in the Automatic. No outside temp is displayed in the ZR1, but is displayed in the Automatic. I understand from previous posts that this means that the control head is not communicating with the programmer.

Are there any further tests I should do before I bite the bullet and remove the programmer?

 

Call Batee.com see what they have to say, that is a good place to get it rebuilt

 

You would have a CCM code if it were a communication issues, you would also have a code for a programmer. Find someone that has a Tech1 scanner or another oem level scanner and go from there. You can also pull codes manually with paperclip. I would not do a thing until you check all the codes and verify no other items are not working . See if you are getting an outside air temp reading on the scanner. What happens when you turn the climate control on auto? Will the temp set display? Could also be a blend door issue but again will get a code stored.

 

It's 100% the programmer, and the issue is 100% the capacitors. Either remove the programmer (I recommend only removing the two circuit boards; this way you don't have to deal with the vacuum block's one-way washer of hell) and replace the capacitors with equivalent parts from Mouser/Digikey, or send it off to BATEE for repairs.

 

The ZR-1 Programmer is different than non LT5's , FYI

 

Earlier C4's with the C68 controller offered a diagnostic mode with various codes and so forth, might check if the later has similar. Found in the Electronics FSM for my '87.

 

The symptom the OP is showing means the Programmer is not functioning--as such there is no way to enter diagnostic mode, since the serial comms are shot.

OP needs to remove the programmer and repair it, either themselves or by sending it to BATEE.

 

Why do you say serial comms are shot? I know the programmer is part of the serial circuit but wouldn't there be a code for serial data line failure plus possible CCM codes? I don't disagree it is likely the programmer, I like to follow the diagnostic tree if possible. (I am meaning with a Tech1 or using the ALDL grounding)

 

Because the head unit communicates with the programmer via a serial data connection. When this connection fails, you get the dashes on the head unit. The cause of this failure is the Programmer's 5V serial data circuit becoming corrupt due to its electrolytic capacitor going out of spec, which, I assume, causes noise on the line that cannot be corrected for.

Replacing the capacitors corrects this issue.

 

Would you not have a Code 41 in the CCM (serial data line failure) ? As long as there isn't an aftermarket radio or a problem with the light driver, you are probably right about the programmer.

 

I think you're confusing something. It's not the data bus; it's a direct connection between the programmer and the head unit.

 

Thanks for all the help. Batee confirms that it is the programmer unit. I have ordered the capacitors and will try the repair myself. I have a fair amount of experience with electronic repair, but removing the unit or the circuit board will be a challenge. Someone suggested that dropping the steering column would help.

 

Do you know what the differences of the ZR1 programmer units are? The control head has a different part number, but both work in my 94 Automatic.

 

So pulling the radio and C68 does not give access to the programmer, if so it sounds like the 2nd worse repair behind the heater core. I read somewhere that to fix the blend door problem you need to snip and reattach the hoses on the programmer.
My car is in parts right now and I haven't driven it in a few years, I'm redoing the interior and was thinking of pulling the C68 and having batee rebuild it for $100. If I remember correctly the up and down temp button was difficult to use(pressing a corner of the button). I don't remember a problem with the blend doors.
Do you think its worth sending out the C68 unit? I'm wondering if the buttons are failing.

 

Sweet thread hijack.

But to answer your questions:

1. It's hard to do the programmer but not impossible; either be a skinny individual, be married to a skinny individual, or hire a skinny individual. I fall into the first category and while it did take sufficient cussing, I removed the PCBs without dropping the steering column. I only removed the hush panel, pushed the wiring harnesses out of the way, depressed the accelerator pedal for more room, inverted the programmer so I could remove the cardboard, unscrewed the PCBs, pulled off the vacuum lines from the vacuum solenoids, and removed the boards. I rate that as nowhere near as hard as the heater core due to not actually having to remove any part of the dash itself to access it.

2. If your issue is the buttons on the head unit, then your issue is not the programmer--it's the head unit. Remove the head unit, disassemble until you can see the traces on the PCB that the buttons contact, and clean the carbon deposits off of them using a pencil eraser or equivalent. You will know the issue is the programmer because you'll get those three dashes on the head unit and nothing will work (and your A/C compressor may randomly stay on for no reason).

3. To fix the blend door motor you do not need to mess with the vacuum block on the Programmer. You just need to replace the blend door motor assembly (which is also a PITA).

Hope this helps.

 

Thank you! I don't like to hi-jack threads, but I thought mine would add to the original post. I may not have the same issue, but your reply could help others

 

Hello,

I have been through the very same thing as of 3 weeks ago. My post is here,

'96 HVAC Vent Control Problem - Page 5 - CorvetteForum - Chevrolet Corvette Forum Discussion

I am almost done with my car. It was a nice sunny afternoon and I thought WTH I will go ahead and fixt the heat defrost problem I have read about. I know how to do it and it should take a few hours and some Corvette Yoga. 3 weeks later I am still waiting on parts. What happened with mine was the CPU on the board of the programmer (unit down by the pedal) was bad. So it wont talk to the dash unit and you get the 3 dashes. It was not doing the three dashes before I started the repair and took it all apart. For some reason when I put it back together the CPU took a crap. I know this because I sent it off to Batee.com and he checked it out. Originally he thought he could repair it because bad resistors or solder joints on the board can cause this condition as well. You really wont know what it wrong until you have it checked. Batee.com is really easy to work with and VERY fair. Since mine is not repairable it makes mine worthless!! That's just super. I called Dino's corvette salvage and he is sending me one they will rebuild and test. Since mine is bad I don't get to claim the $100 core...oh the C4 slaps me in the face whenever it can. The programmer is no longer made so it is expensive. I have seen them for the '96 as high as $500.00 on EBAY with bids on them... '96 like mine is different than the others so it makes it harder to find.

You are going to have to take out the programmer. It sucks but it's part of the C4 game.

WHATEVER YOU DO DISCONNECT YOUR BATTERY WHEN YOU WORK ON ANY ELECTRICAL PART OF THE CAR!!!! Any surge of any kind on hook up can cause issues or burn electrical stuff on these older cars.