Cadillac SRX Stalling & U0100 — From Board Diagnosis to Complete ECM Replacement

Symptoms: Engine Stalling and U0100 Lost Communication Error

The Cadillac SRX would occasionally stall while driving, and sometimes shut off completely. Upon scanning, we discovered trouble code U0100 – "Lost Communication with ECM/PCM A."

What U0100 Means

The U0100 code means that other modules are intermittently unable to talk to the engine control module over the CAN bus network. The ECM is the engine's brain, so when communication is lost, it can cause engine stalling or shutdown.

Our Diagnostic Steps

We performed a complete diagnostic process:

• Scanned all modules in the vehicle
• Verified battery voltage and alternator output
• Located all primary power feeds and grounds for the ECM
• Measured the resistance of the high-speed CAN bus
• Monitored the 5V reference supply from the ECM during road tests

The critical finding: just before the engine would stall, the 5V supply from the ECM would sag and drop out. This indicated the ECM's internal power supply was failing intermittently.

Board Findings: Burned Inductor

After carefully opening the sealed ACDelco E39 ECM, visual inspection revealed the culprit: a burned power inductor in the ECM's power supply section. This coil inductor was charred with obvious heat damage.

The burned inductor in the 5V regulator circuit explained everything – when the coil overheated or failed, the ECM lost its regulated voltage supply, causing the module to reset or shut off.

Decision & Correction

Due to the critical nature of the power supply failure and potential for other heat-stressed components to fail, we recommended complete ECM replacement with a new, fully tested unit.

To ensure seamless transition, we performed full data cloning from the original ECM to the new one, transferring all vehicle-specific data including VIN, immobilizer information, and engine parameters for true plug-and-play replacement.

Results & Owner Outcome

With the new, cloned ECM installed, the Cadillac SRX passed rigorous road tests. The engine ran smoothly with no stalls, no hesitations, and no U0100 codes. The owner was thrilled to have their vehicle back in reliable working order.