2012 Jeep Grand Cherokee Cranks But Won't Start: Fuel Pump Relay Diagnosis

Initial Diagnosis and Symptoms

• 🎯 The 2012 Jeep Grand Cherokee presented with a crank-but-no-start condition, having died on the way to the shop.
• 💡 The original concern was a parasitic draw, but the vehicle became undrivable.
• ⚡ The vehicle cranks normally but does not fire, indicating a potential issue with spark, fuel, or air.

Scan Tool and Initial Checks

• 🔍 A scan tool was used to check for diagnostic trouble codes, revealing multiple cylinder misfires and low voltage codes, likely due to the battery issue.
• 💨 The air intake tube was removed to access ignition coils, and a loose clamp was noted, suggesting previous tampering.
• ⛽ A brief spray of starting fluid (Cosby sauce) did not elicit a start, reinforcing the suspicion of a fuel delivery problem.

Fuel Pump Relay Investigation

• ⚠️ An aftermarket fuel pump relay bypass was discovered, with a toasty wire suggesting a potential issue.
• 💧 Upon closer inspection, the external fuel pump relay was found to be full of liquid and smelling foul, indicating it was likely damaged.
• 🧩 By guessing the correct terminals, a jumper wire was used to activate the fuel pump, confirming it was operational when powered.

Solution and Repair

• 🛠️ A new, 30-amp, five-pin fuel pump relay was installed.
• ⬆️ The new relay was zip-tied in an upright position to prevent future water ingress.
• ✍️ A label was added to the fuel pump wiring for future reference.

Customer Communication and Final Thoughts

• 🗣️ The technician noted that customers often tell mechanics what they think is wrong rather than describing symptoms, highlighting the importance of listening and experience.
• 🚗 The engine cover was missing, but the primary issue was resolved.
• ✅ The vehicle was returned to the customer running and driving, with a recommendation to contact the shop if further issues arose, rather than chasing potential unrelated problems like the original parasitic draw concern.