Hello,

2017 Ford Mustang GT CS Edition blows starter relays or pretends it doesn't have enough power to start the vehicle. Start button is pressed and an audible "Click....Click....Click...." repeats until the start button is pressed again. The vehicle will, without any change or troubleshooting, suddenly start after struggling.

Key points:

• Vehicle sits, undriven, for 1-2 months between start ups
• Stored outside
• 30k miles
• Significant corrosion on battery terminals was cleaned recently
• Starter was swapped, no change
• Blows starter relays once every 1-2 starts
• Two new batteries, no change
• Dealership replaced the BCM, no change
• Alternator and battery checked at autozone, no issues (confirmed by driving)
• Code is thrown occasionally AFTER a failed start, P0186A - Neutral Position Sensor (typical for failed starts on this mustang)
• No other systems are impacted (accessories, or other electro-mechanical devices)

History:
Few years back the starter relay went out after a road trip. The mechanic said it "fried". We thought it was the texas heat combined with the engine heat from a 4 hour drive. Replaced the relay and drove home.

After months of no issues the car left us stranded in a mall parking lot after hours. Swapped the windshield wiper relay and starter relay and drove it home. Replaced the starter relay.

After several more months of no issues The vehicle left us stranded in another parking lot. It was acting like it didn't have power (accessories, dash lights, headlights and tail lights all look good) each press of the start button and the engine struggles to turnover, sometimes not even turning over and just making a "Click....click...click..." sound. Jump started it and drove it home.

Vehicle was rear-ended and when the body shop gave it back to us it wouldn't start. Gave it to the dealership and they threw a starter relay and a BCM at it. Vehicle worked so we drive home.

1 week later, thinking I'm smart, I cleaned the battery terminals and lugs of a LOT of corrosion. We also bought a portable car starter just in case.

1 day later it started great in the morning and left us stranded 1 hour away in the city. It drained the portable starter. Swapped the battery in the parking lot because it was acting like it didn't have any power, "CLICK....click....click..." (battery was 1 month old). Car struggled, I'm annoyed, so I punched the relay/fuse box and it struggled again then.....worked, suddenly. Towed it to an auto shop and they wasted my time so now it's home. When it was being towed back it wouldn't start. The second it came off the tow truck it fired right up.

Theory:
It's a bad ground or bad connection in the starter circuit. Something loose or not making contact. It would explain the repeated overheating/failure of the starter relay including the excessive power draw making you think the battery is low and the starter not activating. Wiring diagrams are great, but it doesn't tell me where the ground points are mounted on this vehicle. Does anyone have photos (I'll accept vague directions as well) of the ground points associated with the starter circuit from battery, through start button to starter? HUGE help.

I'll monitor this thread via the email updates. I should respond once a day and I'll post "The Fix" once I find it.

 

SOLVED



Hope this is helpful to someone.



The issue was caused by poor repair work from the dealership related to the original BCM replacement. The BCM under the hood was replaced at a Ford dealership and most of the electrical connections were loose, which is why punching it caused it to work at one point, but a secondary BCM (?) located in the passenger footwell was not programmed with the primary BCM replacement unit. Supposedly the two modules were not talking to each other. But it didn't stop there....



The steering column security module fault code showed up after both BCM were programmed. After replacing the steering security module, tightening the replaced BCM's connections and reprogramming both BCMs with both key FOBs the car is alive and well. I did read that the steering column fault in later mustangs can happen when a BCM is reprogrammed, but I'm not going to complain anymore.



This solution explains a number of issues like intermittent starting with voltage drawn down <9 V on a new battery and coughing or dying while running or the AC compressor not engaging with the engine running, but the blower fan in the cabin turns on OK. The loose connections on the BCM kept getting bumped and causing components to fail or the connections would lose continuity while driving and leave us stranded, even with jump starting.



Big thank you to Advanced Dynamics in Dickinson, TX. <2 weeks to troubleshoot and replace/repair. They knew their stuff.