2021 Chevy Suburban No Start: Diagnosing a Fuel Delivery Issue

Initial Diagnosis: Cranks But Won't Start

• 💡 A 2021 Chevrolet Suburban with 92,000 miles presented with a "no start" condition, despite cranking.
• ⚡ The issue was confirmed as a fuel delivery problem when the engine briefly started after being sprayed with starter fluid.
• ⚠️ The vehicle had a dead battery and a significant number of diagnostic trouble codes (36), many related to low voltage, which were deemed irrelevant.

Identifying Key Diagnostic Trouble Codes

• 📌 A critical code identified was "Fuel pump power control module, fuel pump speed signal incorrect," indicating the pump was not operating.
• 🔍 Other codes related to communication loss and low battery voltage were present but considered secondary to the primary no-start issue.

Fuel System Analysis and Testing

• 📊 Live data showed the fuel pump was commanded off, and the fuel rail pressure remained at 0 PSI when cranking.
• 🔬 The vehicle utilizes a three-phase DC brushless fuel pump, a system the technician was not previously familiar with.
• 🛠️ Factory service data provided limited diagnostic steps, primarily focusing on continuity checks of the pump wiring and suggesting replacement of the control module or pump if issues persisted.

Challenges with Fuel Pump Control Module Bracket

• ⚠️ A significant challenge encountered was the design of the fuel pump control module bracket, with bolts installed from the inside out of the frame rail, making removal difficult without specialized tools or destructive methods.
• 🔩 The technician opted to replace the stripped bolts with standard nuts and bolts, acknowledging this would complicate future repairs.

Fuel Pump Motor and Control Module Assessment

• ⚡ Resistance tests on the fuel pump motor windings showed low ohms (around 3-3.4 ohms) between the three phases, suggesting the motor circuits were intact.
• ❓ The technician suspected the fuel pump control module was faulty, as powers and grounds to the module were confirmed good, and the motor windings tested within expected parameters.
• ✅ The decision was made to replace the fuel pump control module, with the expectation that this would resolve the no-start condition.

Post-Replacement and Future Diagnostics

• 🚀 After replacing the fuel pump control module and reassembling, the Suburban started and ran, with scan data showing expected fuel pressure and current draw.
• 🧠 The technician expressed a desire to learn more about diagnosing three-phase brushless DC fuel pumps and their controllers, noting the limitations of standard service data for inoperative systems.