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.
2000 Cadillac Seville STSFACTORY OEM SERVICE PROCEDURE
Scan Tool Does Not Communicate With Class 2 Device
- If scan tool powers up, go to next step. If scan tool does not power up, go to SCAN TOOL DOES NOT POWER UP .
- Turn ignition on. Attempt to establish communication with each module located along the class 2 serial data line. See CLASS 2 SERIAL DATA LINE under OPERATION. If scan tool does not communicate with any modules, go to next step. If scan tool communicates with some or all modules, go to step 7 .
- Select DISPLAY DTC function for each module. If using a TECH 2 scan tool, select CLASS 2 MESSAGE MONITOR feature. Record all DTCs and what module they are set. If any DTCs from U1000 through U1255 are set, go to next step. If no DTCs from U1000 through U1255 are set, go to step 6 .
- If only DTC U1000 or U1255 is set, go to DTC U1000 & U1255: CLASS 2 COMMUNICATION MALFUNCTION under DIAGNOSTIC TESTS. If DTCs between U1000 and U1255 are set, go to DTC U1001-U1254: LOSS XXX COMMUNICATIONS under DIAGNOSTIC TESTS.
- Diagnose concern using DTC U1001-U1254: LOSS XXX COMMUNICATIONS procedure under DIAGNOSTIC TESTS. After repairs, go to appropriate diagnostic system check for module that set DTC.
- Turn ignition off. Disconnect scan tool from Data Link Connector (DLC). Check for poor connections at DLC terminals No. 2 (Purple wire) and 5 (Black/White wire). If connections are okay, go to next step. if faulty connections are found and repaired, go to appropriate diagnostic system check for module that set DTC.
- Check for open in Black/White or Black wire between DLC and ground connections G200 and G201. See Fig 1 . If circuits are okay, go to next step. If faulty circuit is found and repaired, go to appropriate diagnostic system check for module that set DTC.
- Check for open, short to ground or short to voltage in Purple wire between DLC and 30-pin in-line connector located in the instrument panel harness under right side of instrument panel near rear of glove compartment. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. If circuits are okay, go to next step. If faulty circuit is found and repaired, go to appropriate diagnostic system check for module that set DTC.
- Disconnect Powertrain Control Module (PCM) connectors. See COMPONENT LOCATIONS . Using scan tool, attempt to establish communications with Dash Integration Module (DIM). If scan tool communicates with any module, go to next step. If scan tool does not communicate with any module, go to step 11 .
- Replace PCM. See POWERTRAIN CONTROL MODULE under REMOVAL & INSTALLATION. After repairs, go to step 66 .
- Disconnect Electronic Brake Control Module (EBCM) connectors. See Figure . Attempt to establish communications with Dash Integration Module (DIM). If scan tool communicates with any module, go to next step. If scan tool does not communicate with any module, go to step 14 .
- Check for short to ground or short to voltage in Purple wire between EBCM connector C2 terminal No. 21 and PCM connector C1 terminal No. 18. See Fig 2 and Fig 3 . See appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. If circuit is okay, go to next step. If faulty circuit is found and repaired, go to step 66 .
Factory Service Tools
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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.