A 2001 Cadillac Seville SLS with just over 100,000 miles arrived at the shop with a no-start condition. The owner reported intermittent starting issues, often resolved by disconnecting and reconnecting the battery. A battery charger connected to the car hinted at a potential battery problem. However, the issue extended beyond a simple battery failure; none of the car’s electronics were functioning. This article details the diagnostic process and solution for this 2001 SLS Cadillac.
Diagnosing the Communication Failure
The first step was to connect a Tech2 scan tool to check for Diagnostic Trouble Codes (DTCs) and assess module communication. A Class 2 DTC check revealed a complete lack of communication with any modules.
Common issues in these vehicles include faulty ignition switches and water damage to modules, often caused by windshield or passenger door leaks affecting the SRS module. However, the SRS module was dry. Using an oscilloscope on pin #2 of the Data Link Connector (DLC) showed a constant 12V, indicating a short to power on the Class 2 communication line.
Isolating the Faulty Module
The Class 2 communication network in this Cadillac utilizes a loop configuration, where the communication line passes through each module. This allows for redundancy but can complicate diagnostics. After visually inspecting harnesses and grounds, each module was systematically disconnected to isolate the source of the short. Disconnecting the Powertrain Control Module (PCM) restored a normal Class 2 waveform on the oscilloscope.
Further testing confirmed power, ground, and 5V reference voltage at the PCM connector were within specification, pointing to an internal PCM failure.
Replacing and Programming the PCM
A used PCM was chosen as a cost-effective replacement. Crucially, any replacement PCM, whether new, remanufactured, or used, requires proper setup with the vehicle’s VIN and calibration data, as well as theft system relearning. A Midtronics battery maintainer was used to ensure stable voltage during programming.
The Tech2, in conjunction with the TIS2000 software, was used for remote programming. The correct calibrations were downloaded to the Tech2 and then uploaded to the vehicle’s PCM. To prevent interference from other modules during programming, the I/P (Instrument Panel) fuse was removed, temporarily silencing communication from potentially disruptive modules.
Completing the Repair: Theft Relearn
After successful PCM programming, the engine still would not start due to the vehicle’s anti-theft system. The Tech2 was again utilized to perform a theft relearn procedure using a fast learn method. Once completed, the 2001 Cadillac Seville SLS started and ran without issue. All codes were cleared, and post-programming procedures like oil life reset were performed.
While the immediate issue was resolved, replacing the aging battery was strongly recommended to prevent future problems. This case study highlights the importance of systematic diagnosis, the use of proper tools and procedures when dealing with complex electronic systems, and the crucial role of PCM programming and theft relearn procedures in resolving no-start conditions in a 2001 SLS Cadillac.
