Owner's Problem Description
The owner reports that the vehicle cranks and starts with starting spray, but the fuel pump isn't receiving power. A new fuel pump was installed, yet the issue persists. The fuel pump relay sounds like it is activating but not supplying power to the pump. The owner is unsure of the next steps and is concerned about the safety of bypassing the relay with a direct battery connection.
Professional Technical Analysis
The 2002 Oldsmobile Bravada, equipped with a 4.2L inline-six engine and approximately 120,000 miles, is experiencing a no-start condition with fuel pump engagement issues. The owner noted that the vehicle will only start with starting fluid, indicating a lack of fuel delivery. The fuel pump was replaced, eliminating the possibility of a defective pump. Despite this, the pump is not receiving power, suggesting a possible fault in the fuel pump relay circuit or related wiring. The fuel pump relay is suspected to be malfunctioning, as it activates but fails to maintain power to the pump. This can be attributed to several factors: a faulty relay, poor connections, or issues within the vehicle’s PassLock system, which may inhibit fuel delivery if it perceives a security threat. Electrical testing is crucial; the relay should be tested for proper function and power supply at both the input and output terminals. Additionally, the gray wire supplying power to the pump must be inspected for shorts or damage, especially where it routes through the vehicle. Given the vehicle's age and the potential for corrosion and wear, connections should be thoroughly examined. If the PassLock system is active, it can prevent fuel pump operation, further complicating the diagnosis. A reset of the PassLock may be necessary if it was inadvertently triggered during valve cover gasket replacement, as this could have disturbed wiring or connections. Prioritizing electrical integrity and proper relay function is critical for resolving this issue and ensuring safe operation.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Relay Failure: The relay may be malfunctioning, failing to maintain power to the fuel pump despite activation. Testing should confirm operation by checking for voltage at the relay output when activated. If voltage is absent, the relay is likely faulty. Replacement part can be OEM P/N 15119709, typically costing $30-60. - Relay clicks upon activation but no power at fuel pump connector, intermittent relay operation.
- Wiring Issues: Damaged or corroded wiring leading to the fuel pump can cause intermittent power loss. The gray wire should be inspected for continuity and shorts, especially at common failure points such as connectors or points of abrasion. This could lead to insufficient voltage reaching the pump. - Visual inspection reveals frayed wires or poor connections, voltage drop during cranking.
- PassLock System Activation: If the PassLock system is engaged, it may prevent the fuel pump from operating, thinking there is a security breach. Resetting the PassLock may be necessary, usually by turning the key to the ON position for 10 minutes without starting the engine, then turning it off. - Check engine light on, security light blinking, potential stored codes related to PassLock.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Inspection: Begin by inspecting fuses and connections related to the fuel pump relay. Use a multimeter to check for continuity in the relay circuit and ensure the relay is receiving power. Inspect the gray wire leading to the fuel pump for any signs of damage or corrosion.
- STEP 2 - Relay Testing: Test the fuel pump relay using a multimeter. Check for voltage at the relay output when activated. If no voltage is present, replace the relay with a known good one. If the problem persists, further investigation into the wiring is required.
- STEP 3 - Wiring Inspection: Inspect the wiring harness leading to the fuel pump for shorts or breaks. Pay particular attention to areas near connectors or points where the harness may rub against metal surfaces. Repair any damaged wiring as necessary.
- STEP 4 - PassLock Check: If the issue remains unresolved, check for PassLock system engagement. Reset the system if necessary by following the manufacturer’s procedure. This may involve a specific key sequence to reset the security system.
