The year 1970 was a pivotal one for the U.S. auto industry. With new car designs already on the assembly lines, Congress threw automakers a curveball by passing the Clean Air Act and establishing the Environmental Protection Agency (EPA). Thus began a series of new federal emissions standards and maintenance requirements that would gradually roll out over the next decade.
Because of these progressively rigid standards, automobiles needed to become more sophisticated. Manufacturers started installing electronic computer controls on their vehicles to monitor engine functions and diagnose engine problems. This On-Board Diagnostic (OBD) system was necessary to keep everything performing properly and to alert the driver when it was time to seek the aid of a mechanic.
The Instrument Panel Cluster...
The Instrument Panel Cluster (IPC) has the ability to display diagnostic trouble codes (DTCs) from the various modules that transmit them. For C5s built before 12/15/97, there are 48 different DTCs; later C5s equipped with the Active Handling option have a few more. A full list of these DTCs can be found in your car's service manual.
In the '90s, the feds buckled down even further, requiring that all cars and light trucks sold in the United States after January 1, 1996, be equipped with more-sophisticated OBD II monitoring equipment and a built-in diagnostic port. This port--typically referred to as the ALDL, or "Assembly Line Diagnostic Link"--is used for retrieving powertrain information with a scan tool.
To ease the diagnostic process, federal regulations dictate that the ALDL must be located within three feet of the driver and that it not require any tools to be accessed. When an OBD I or OBD II system detects a powertrain problem, it logs it as a fault code in the vehicle's computer memory. When retrieved, this code provides information regarding the source of the trouble.
The EPA estimates that more than 6 million Americans are currently driving cars with a "check engine" or "maintenance required" light illuminated. The cause could be as benign as a loose gas cap or as serious as an internal powertrain problem. Being able to quickly retrieve and interpret the fault code(s) behind that check-engine light could get you back on the road in a few minutes or even save your engine.
As mentioned earlier, you can use a scanner to retrieve codes via the vehicle's ALDL. Scanners can be costly to purchase and maintain however, and are therefore typically purchased only by mechanics. Fortunately, there is a way for you to find the codes in the computer's memory by using the programming buttons on your dashboard. The following directions will guide you through this easy task.
For a complete list of C5 trouble codes, visit www.vetteweb.com.
You can enter the Diagnostic Display mode using the following procedure:
1. Turn the ignition to the "On" position but don't start the engine.
2. Press the "Reset" button on the Driver Information Center (DIC) to turn off any existing warning messages.
3. Press and hold the "Options" button.
4. While holding the "Options" button, press the "Fuel" button four times within a 10-second period.
The onboard diagnostics system will go into the "Automatic" mode, which shows each module's DTCs in a preset sequence:
1. 10 - PCM (Powertrain Control Module)
2. 28 - TCS (Traction Control System)
3. 38 - RTD (Real Time Damping. Some models do not have this option.)
4. 40 - BCM (Body Control Module)
5. 60 - IPC (Instrument Panel Cluster)
6. 80 - Radio
7. 99 - HVAC (Heater Vent-Air Conditioning)
8. A0 - LDCM (Left Door Control Module)
9. A1 - RDCM (Right Door Control Module)
10. AC - SCM (Seat Control Module)
11. B0 - RFA (Remote Function Actuation)For each module, all existing DTCs will be displayed. If no faults are present in a particular module, you'll see "No More Codes" on the IPC display.
There are two kinds of DTCs....
There are two kinds of DTCs. The first is a "Current" code, which is designated with a letter suffix "C." A Current code indicates a malfunction is present at this time. The second is a "History" code, which is designated with a letter suffix "H." A History code indicates that a malfunction was present at some time in the past 40 to 50 ignition cycles. A history code could indicate the presence of an intermittent fault.
Once the system has displayed...
Once the system has displayed all the modules, it will go into the "Manual" mode. This allows you to select each module individually using different combinations of DIC buttons. Manual mode can also be entered during the Automatic sequence by pressing any button except "E/M." (Pressing E/M will cause you to exit the diagnostic mode.) When the display shows "Manual Diagnostics," select a module by pressing the "Options" button to scroll forward, or the "Trip" button to scroll back. Once a module is selected, the DTC(s) from that module will be displayed. If more than one code is present, press "Gauges" to scroll forward or "Fuel" to go scroll back. To exit the diagnostic mode at any time, press "E/M."
If you want to erase the DTCs...
If you want to erase the DTCs in a given module, press and hold the "Reset" button until the display reads "No More Codes." Keep in mind that clearing a trouble code doesn't repair the underlying problem.
Now that you've retrieved...
Now that you've retrieved your C5's DTCs, the next step is to narrow down the possible causes. If you're a DIY'er, you may wish to purchase a scan tool capable of performing more-in-depth diagnostics. The tool will plug into the ALDL, shown here.
We chose the Actron Elite...
We chose the Actron Elite AutoScanner Pro (PN CP9190) for its impressive power and versatility. The AutoScanner Pro can record and graph data, it works on all OBD II-equipped (and most domestic OBD I-equipped) vehicles, and it's even updateable via the Internet. At less than $550, it's also relatively affordable.
Once you've located your C5's...
Once you've located your C5's diagnostic port, simply plug in your scan tool and follow the on-screen directions. While we don't have room here to list all of the C5 DTCs, you can find them at www.vetteweb.com. Additionally, the AutoScanner Pro boasts a built-in code library.