When A “Stealth” Tune is NOT

Vince Geglia, Owner

Trifecta Performance, Inc. (www.trifectaperformance.com)

05/03/2009 (updated 08/03/2009)

Disclaimer: The authors have taken every measure possible to ensure the accuracy of the information presented here, but cannot be held responsible for any inaccurate information presented. In other words, proceed at your own risk.

NOTE: This article discusses the dangers of a “conventional” stealth tune on Delphi controllers and does not apply to Trifecta Performance’s “hide-a-tune”, released recently for the LNF (2.0 DI Turbo) engine using a Bosch engine controller which is 100% safe and undetectable using current detection methods.

Introduction – What is a “stealth” tune, why is it popular and problems with them?

There are tuning companies now offering custom tuning where the claim is it is “stealth”, or, cannot be detected by dealership service department equipment. While it is true that technically this type of tune will pass the dealership’s service department tests for non-factory tuning, it also instills a false sense of security with customers that choose to buy them. This technical article explains how “stealth” tunes work, why they can pose a safety hazard, and alternatives to the enthusiast that doesn’t want to risk warranty invalidation or safety hazards.

The Factory Warranty Issue

If a vehicle owner walks into a dealership today and asks them how getting a custom tune might affect the factory warranty, the answer usually is something like this: “If you even THINK about reprogramming your vehicle’s computer we will invalidate your entire warranty.”

This is generally untrue – our understanding of warranty law is that it is illegal for auto manufacturer to invalidate a warranty simply on the basis of evidence of an aftermarket part (including a custom tune) installed on the vehicle. However, if there was a high dollar warranty claim, for, say, an engine failure AND the dealership found a custom tune installed in the ECM, one should expect that the dealer and manufacturer might try to blame the failure on the custom tune regardless of cause.

Most enthusiasts want to walk the fine line – they’d like to have custom tuning for their vehicle but would also like to avoid a situation where the factory might try to invalidate the warranty.

Of course, the 100% foolproof approach is to simply not modify the vehicle. The next best thing might seem like a “stealth” tune where a custom tune can be installed on the vehicle but is undetectable to dealership tools.

The Calibration Verification Number (CVN)

Every vehicle’s program written by the manufacturer has a “code” associate with it called a Calibration Verification Number, which is abbreviated to CVN. To see this in action, go to http://tis2web.service.gm.com/tis2web, enter the VIN for your vehicle, select ECM (Engine Control Module) and see what is displayed. Below is the sample output for a 2008 Chevrolet Corvette:

Note above the CVN – 00004C74. Now, take a look at the hex representation of the header of the tune from this vehicle:

Notice that last two bytes? 4C 74 – that’s the CVN stored in the tune for this vehicle. It matches what GM has on file! That means this is a legitimate GM tune.

When the ignition switch is turned on, the ECM (or TCM) performs a complex mathematical operation on all the data stored in the module and then compares it to the CVN stored in the memory. If the calculated CVN doesn’t match the CVN, the module will shut down, and set a P0601 diagnostic trouble code. It shuts down because the mismatch may indicate there has been a memory failure within the module.

Software that modifies the tune in a module needs to calculate the new CVN value, and update it in the tune to avoid the P0601 DTC. The problem with this is that now the CVN in the tune doesn’t match the one GM has on file for that vehicle.

What information can the dealers get out of the tune?

Dealerships use a tool called the Tech2. It is capable of reading the CVN reported by the ECM (or TCM). Dealers are trained to check the CVN in an ECM (or TCM) and compare them against the factory values, particularly if there is a suspicious warranty issue. Dealers are also instructed to compile evidence of this mismatch (by taking a picture) and documenting the case so the manufacturer can better refuse a warranty claim.

How “stealth” tunes can prevent the dealer from detecting a tune, and why it is unsafe

It is possible to set a flag in the ECM (or TCM) that tells it to ignore the fact that the CVN in the tune doesn’t match the calculated CVN for the tune to avoid the P0601 and the ECM shutdown. “Stealth” tunes set this flag and program stock CVN values into the ECM (and TCM).

If the dealer attempted to compare the ECM (or TCM) CVN values, even though they are incorrect for the tune file, they still match the values the manufacturer has on file for the vehicle.

However, there is a major drawback to using this approach… Part of the reason the CVN exists is to validate that there hasn’t been a failure of the ECM (or TCM) memory. If the EEPROM chip (the programmable chip that holds the tune information) becomes corrupted, it could cause a major problem – at best the engine would run incorrectly, at worst it could pose a safety hazard. Imagine this scenario – the part of the memory that controls the electronic throttle becomes corrupt – without a “stealth” tune the ECM would set a P0601 and simply shut the engine off. With a “stealth” tune, the ECM would be allowed to continue operating despite the memory corruption and it is possible the throttle could go wide open and stay that way!

Safe alternatives to “stealth” tunes

It is generally a good idea to leave the CVN calculations enabled to help prevent vehicle damage or safety issues in the event there is a malfunction of a control module. So, how does one run a custom tune and alleviate the risk of warranty invalidation with the dealer? There’s two basic choices:

Buy a spare ECM/TCM and have it programmed with the custom tune

Spare ECM/TCMs are generally available either from salvage yards, the dealership parts department, or, in some cases, even the local auto parts store.

Pros: Very easy to do, doesn’t require any additional computers, cables, software, etc.

Cons: Expensive – brand new ECMs can cost as much as $700. Some TCMs cannot be removed from the transmission (e.g. 6 speed automatic). May require a trip to the dealer for “crank relearn”.

Buy a programming cable and use it to switch between tunes at will

Trifecta Performance offers a programming cable option with all custom tunes that works on a Windows XP or Windows Vista laptop that has a USB port at a very reasonable price (less than most ECMs cost). Before going to the dealer, the vehicle owner can use the programming cable to reprogram the ECM back to the stock tune in less than 10 minutes.

Pros: Low cost, convenient. No relearn procedures are necessary, no ECM/TCM swap needed.

Cons: Requires a laptop computer.

Conclusion

Custom tuning is an exciting way to add more power to an enthusiast’s vehicle. By choosing a competent custom tuner and a reprogramming solution, many of the issues with dealership service visits can be negated without risking vehicle damage or personal/property safety.