To check for Diagnostic Trouble Codes stored in the computer, turn the ignition on, then hold down the OFF and WARMER (for digital dash) or OFF and passenger-WARMER buttons (for analog dash) or OFF and "Info ^" buttons (if you have temperature dials) until all of the dash lights come on. The digital display will then show any codes stored. Be prepared to write them down. When it's done, you will probably see "PCM?" At that point, press the OFF button 3 or 4 times until the dash goes back to normal, or just turn off the ignition.

If you've checked for codes and found some, this is what you need to look up what they mean:

If your car is a 1996 model or newer, go here: (OBDII) (P codes only, but with diagnostic help.)

This link includes ALL codes (P, B, C, and U codes)

If your car is 1995 or older, go here (OBDI)

Once you have looked up what the codes mean using the web sites listed above, you may be able to figure out exactly what needs to be done by the definition of the code. If you have any questions on what it means or how to fix it, come back to your forum question and post the code and the definition. More than likely, someone will be able to tell you exactly what needs to be done. We will do our best to help.

Good luck!

************************************************** ************************************************** **

Courtesy of JimD

DTC display; 1998-2004 Seville, 2000-2005 Deville and other models with 3 buttons on the RH side of DIC

Use the 3 switches located to the right (LH drive cars) of the Driver Information Center (DIC) to activate and respond to the OBD prompts on the DIC.

INFO DOWN or INFO UP = manual toggle

Ignition ON, acknowledge any warning messages; press ON/OFF and INFO UP together for 2 to 3 seconds. Everything in front of you lights up for 4 or 5 seconds, then you will see:

Display shows "ALL?"

Answering YES will display "ALL CODES?"
Answering YES will run automatic test sequence and display codes, if any. Systems and codes will scroll faster than I am able to read them and write them; not to worry.
"CLEAR ALL CODES?" will display at the end of the automatic test. If you are satisfied you have the information you need, answer YES to clear/erase all error codes.

Answering "ALL?" with INFO DOWN will toggle systems test manually in order.
Answering "ALL?" with INFO UP will toggle system test manually in reverse order.

Press INFO RESET to reset DIC to "ALL?" to start again.

Ignition OFF to exit.

SYSTEMS: (as of 1998)

ABS (Antilock Brake System)
AMP (Amplifier)
DDM (Door Driver Module)
DIM (Dash Integration Module)
IPC (Instrument Panel Cluster)
IPM (Instrument Panel Module)
IRC (Integrated Radio Module)
PCM (Powertrain Control Module)
RFA (Remote Function Actuation)
RIM (Rear Integration Module)
SDM (Sensing and Diagnostic Module) Includes airbag crash data. Under RF seat
VTD (Vehicle Theft Deterrent)
MSM (Memory Seat Module)
TTM (Tilt/Telescoping Module)
RSS (Road Sensing Suspension)

"History" means that the fault is no longer detected. It will stay in history for 50 ignition cycles then be deleted unless it becomes "Current" again or is cleared manually.

If you need advice after a code pull, post your found codes and definitions in your proper forum.

How to video.

************************************************** **************************************************

Courtesy of Submariner409

In the 1998 - 2004 models with the 3 DIC control buttons, if you enter the code sequence and answer the ALL CODES ? with NO, that allows you to use the buttons to scroll to/back to each module individually in alphabetical order (no auto-scroll) and work with/delete codes in that module only. You then use YES, NO and ^/v to step to the next module. This way you have more time to write down codes and you do not need to clear ALL CODES.

************************************************** ************************************************** **

Pre '98 Sevilles
Courtesy of N*Caddy

Here is a image I posted some while back (back when my car had no BOSE) and it couldn't show in a much suggestive matter how to access your diagnose mode (where you can read the codes):

Don't worry you can NOT hurt anything.

First turn the key to ON (you can either start the engine or not important key is in ON position)
Follow the steps in the picture:
Step A. After 2-3 seconds of holding the two buttons shown the whole dash board (lights displays) will turn on for 2 seconds or so. IS OK!! is just a test to make sure that all lights and display pixels/elements are working.
Step B. Point your attention to the display strip on the IPC and you will see something like:
"B1234 Current"
"C4321 History"
Each code will be shown for 1-2 seconds so you have to have a fast eye and a paper with a pen to write them quickly. Alternatively use some cell phone (or what ever device) to film the sequence.
Once the codes are finished and the enumeration will stop and the display will show something like "PCM?" then that's it the codes are finished you can just turn OFF the key and exit the Diagnose procedure.
Alternatively press "OFF" on the climate control and Diagnose mode is restarted (i.e. all the dash lights/displays are on). While all the lights are one press again "OFF" and you are out of the Diagnose mode. At ANY time you can just turn the key to OFF and that's it.
By the way, since yours is a '96 it will display the codes as a 2 letters followed by a 4 digit number rather than one letter and 4 digits as in the '97 and newer.

The whole procedure last 1 minute, is something you can do just before stepping out of the car once you park it on the drive way.