WHT Z06 Mods:
Disable CAGS

[1 -> 4] Computer aided gear selection (CAGS) is a hack invented to avoid the gas guzzler tax. A solenoid is used to lock out second and third gears when the following conditions are met:

Note that the actual parameters can vary depending on application; these are the values for the 2007 Z06.

During the lockout, a dashboard light that says "1 → 4" is illuminated and you are supposed to shift from 1st directly to 4th. There is no timeout; that is, the lockout continues as long as the above conditions persist.

[CAGS Kit] The good news is that it's easy to defeat CAGS. Prior to 1996 when OBD-II went into effect, one could simply unplug the CAGS solenoid connector. However, OBD-II is required to detect failures that impact emissions, so disconnecting the CAGS solenoid on a 1996 or newer manual transmission Corvette will throw a P0803 trouble code (Skip Shift Solenoid Control Circuit) and cause a service emissions system (SES) warning light. A number of companies (including Chevrolet) sell !CAGS kits. Early kits consisted of a connector with a 24 Ω potted resistor to simulate the electrical load of the solenoid. Unfortunately, at 13.7 volts this works out to 571 mA or 7.8 watts and the resistor used is typically only rated for ½ watt. This means the resistor gets pretty hot and eventually burns out. Recent versions of the kit use a 2.2K Ω resistor which results in a more reasonable 6 mA of current.

The CAGS resistor fuse

More recently, a clever person realized that the CAGS circuit on the C6 Corvette has a dedicated fuse and that it is possible to add a resistor to the fuse and leave the solenoid connected; thus was born the "CAGS resistor fuse". The first one I saw was in a post on corvetteforum.com and it used a ¼ watt resistor hung off the top of the fuse. Here's one I made using a 20K Ω resistor.

[CAGS resistor fuse]

[CAGS fuse] My first refinement was to use a 0805 SMD resistor which is 2 X 1.25mm and fits nicely inside the fuse.

How to make a CAGS resistor fuse

Adding a SMD resistor to a mini fuse is only a little bit tricky. 2.2K Ω at 13.7 V is about 6 mA or 0.085 watts; the SMD resistor is rated for 0.125 watt. Since it's only being used for its shell, the current rating of the fuse isn't important but sticking with the stock 10 A part does make the finished product stealthier.

Surface mount soldering isn't that difficult. Here's a really good video called Tangent Tutorial 3: Surface Mount Soldering Techniques:

[Surface Mount Soldering movie]

This is my favorite skip shift solution. It's cheap to try; the fuse costs less than $1 and the resistor is about 5¢.

Installation

Note: Remember that ultimately you are responsible for modifications you make to your own car so if you have any reservations about the information contained on this webpage, don't modify your car!

Once you finish making your fuse, install it in position #10 of the underhood fuse block:

Underhood fuse block Fuse assignments

Important: The underhood fuse box is labeled with numbers and letters to identify connector positions. Fuse #10 uses pins D12 and E12. The 10 A fuse next to the "10" (pins A10 and B10) is actually #8 and if you install your CAGS fuse there, you'll disable your parking lights! This is the mistake most people who have trouble make.

Testing

CAGS is one of those things that can be difficult to demonstrate on command. Here's a recipe that should help:

As it turns out, you can actually launch any manual transmission car with no throttle. This is an actual exercise used at Spring Mountain to familiarize students with the exact point of clutch engagement.

The CAGS LED Fuse

I think the CAGS resistor fuse is the way to go; but for a variety of reasons, some folks didn't want to make their own so I kept searching for a solution that didn't require soldering.

[Littelfuse] I've always been intrigued by the Littelfuse SmartGlow Fuse which "glows when it blows." It seems pretty cool; it's got an LED (actually two) but also it also seems a waste that you only get to see a LED light up when you've blown the fuse. It's really kind of dumb! I mean, once it does its thing, you toss perfectly good LEDs into the trash. That's just not right.

But one day it occurred to me that this is the perfect off-the-shelf solution to the skip shift problem.

How to make a CAGS LED Fuse

Executive summary: Really, the hardest part of this mod is blowing the fuse. Here are a number of techniques.

The Old School Method

Here's how to do it:

It's important for you to see that the LED lights up and at the same intensity; if it doesn't, you've done something wrong.

It's a good idea to flip the fuse around and test the other LED; see CAGS LED Fuse Notes for more information.

Here are some pictures of the process. I used a scan tool (EFILive's FlashScan) to turn the CAGS circuit on for the last one:

Preparation Blown SmartGlow Fuse CAGS circuit hot

A small arc is created when you blow the SmartGlow fuse; this may leave a tiny divot in the fuse and whatever positive voltage source you're using. This can be avoided by arcing against sacrificial pieces of metal such as two coins. Wrap your wire around one terminal of the fuse, tape the other end of the wire to a ground source then hold a penny against the positive source with one hand and another penny against the other fuse terminal (be careful not to let the penny touch both fuse terminals!) Then touch the pennies together.

The Car Battery Charger Method

A corvetteforum.com member suggests using a car battery charger to blow the fuse. Connect the clips to the fuse and plug in; the fuse blows with no (external) sparks. This is one of the better methods I've heard of.

You do need to use a charger that can supply sufficient current. My charger is an antique that once belonged to my grandfather and is only rated for 6 amps but worked, as Grandpa would say, "Just dandy."

Important: Running too much current through a LED will shorten its life or even burn it out. Using a voltage source that ouputs significantly more than 13.7 V will increase the current across the LED and can damage it. Some jump starters output 24 V and this higher voltage setting should not be used when blowing your fuse.

The Physical Break Method

Use a drill, Dremel tool, knife, etc to physically sever the fuse element. Note that you should still test that the fuse glows when 12 V is applied.

The Auto Parts Store Method

Several people have used another successful strategy: ask the store you buy your SmartGlow fuse from to hook it up to a battery charger and blow it for you. This has the advantage that you can install immediately the fuse before leaving the store parking lot. Plus it's worth it just to hear them say, "Wait, what now?"

After blowing the link in the fuse, install as described above.
[CAGS fuse]

When Things Go Wrong

The #1 reason people fail to get a CAGS LED Fuse to work is that they install it in the wrong position; see installation for details.

A few people have complained that they install a CAGS LED Fuse and weeks or months later they get an engine check light. A few of them sent me their failed fuses so I could investigate.

Smart fuses contain two LEDs, one for each polarity (see CAGS LED Fuse Notes for the gory details). What I found is that one of the LEDS in failed fuses lights up but is very dim. Apparenlty something has damaged but not killed either the LED or the resistor and this causes a much lower current draw and this makes the ECM think the solenoid has failed. Flipping around or replacing with a new CAGS LED Fuse will fix this.

Note that my Z06 is my daily driver and I've been using the same Littelfuse SmartGlow Fuse for years. So if you have one fail, just replace it.

CAGS LED Fuse Notes

Other LED fuses

There are other companies that make LED indicator fuses:

Other Skip Shift Disable Methods

Here are some other skip shift delete methods I haven't covered yet:



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Craig Leres