Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Cathode Ray Tube Controller
In order to access and control the BCM self-diagnostic features, 2 additional electronic components are used. The 2 components are the Cathode Ray Tube Controller (CRTC) and Cathode Ray Tube (CRT) picture tube. The CRT's "SERVICE MODE" incorporates a 22-character display area, which is used to display diagnostic information. When a malfunction is sensed by the computer system, one of the driver warning messages is displayed on the CRT under the "DIAGNOSTIC" category. When the "SERVICE MODE" is entered, various BCM, ECM or IPC faults can be displayed. In addition to the parameters, fault codes, inputs and outputs, are other features such as override commands, snapshot, display VIN and code clearing capability. This information can be accessed and displayed when commanded through the CRT. The CRT becomes the device in which to enter diagnostics and access service diagnostic routines. The CRTC is the device which controls display and interprets switches touched on the CRT. CRTC passes this information to the BCM. This communication process allows the BCM to transfer any of its available diagnostic information to the CRT for display during "SERVICE MODE". By touching the appropriate pads on the CRT, data messages can be sent to the BCM from CRTC over the data line, requesting specific diagnostic features. Below is a list of computer controlled subsystems.
- Climate Control
- Instrument Panel Displays
- Illuminated Entry
- CRT Display
- Chime
- Dimming (Lighting)
- Twilight Sentinel
- Cruise Control
- Courtesy Lights
- Compass
- Generator Control System
- Self-Diagnostics System
- ECM Subsystems
- Radio
- Gauges
- Trip Data
- Driver Diagnostics
- Phone
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.