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2018 F-150 Lariat: Battery Saver Mode keeps popping up, slow crank, new battery already!

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Mark S. · rep 0 · May 22, 2:12 AM · 1 replies · solved · Question

Vehicle: 2018 Ford F-150 Lariat

Hey everyone, I'm pulling my hair out with my 2018 Ford F-150 Lariat, 3.5L EcoBoost. For the past few weeks, I keep getting 'Battery Saver Mode' warnings on the dash, especially after short drives or if the truck sits for a day. Sometimes it cranks really slow, almost like it won't start, but then it usually does.

I thought it was just the original battery, so I went ahead and replaced it with a brand new Motorcraft battery about a month ago. Everything seemed fine for a bit, but now the warnings are back, and the slow cranking is happening again. I've checked the battery terminals, and they're clean and tight. I also made sure all accessories are off when I leave the truck.

Could this be an alternator issue, even though the truck isn't completely dying? Or something else electrical? Any ideas on what to check next before I take it to the dealer?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:12 AM

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Hello Mark S., it sounds like you're dealing with a frustrating intermittent charging system issue on your F-150. While replacing the battery was a good first step, the recurrence of the problem suggests a deeper electrical fault. Here's a diagnostic approach:

  1. Check Battery Monitoring System (BMS) Reset: After replacing the battery, the BMS often needs to be reset so the vehicle knows it has a new battery. This can sometimes be done via a specific procedure (e.g., flashing high beams 5 times, pressing brake 3 times, etc., consult your owner's manual or a Ford-specific resource) or with a diagnostic scan tool. If not reset, the system might still be managing the new battery as if it were old.

  2. Inspect Alternator Output: Even if the truck isn't completely dying, a failing alternator can have intermittent output. A local auto parts store can often perform a free charging system test. Alternatively, use a multimeter to check voltage across the battery terminals with the engine running. You should see around 13.5-14.8 volts. If it's consistently lower or fluctuates wildly, the alternator is suspect.

  3. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any stored codes, even if the check engine light isn't on. Relevant codes might include P0562 (System Voltage Low), P0620 (Generator Control Circuit Malfunction), or U012A (Lost Communication with Generator Control Module).

  4. Test for Parasitic Draw: A component staying on when the vehicle is off can slowly drain the battery. This is more complex to diagnose and involves using a multimeter in series with the battery to measure current draw. A healthy draw is typically under 50mA after the vehicle has 'gone to sleep' (usually 15-30 minutes after turning off).

Likely Causes:

  • Failing Alternator: Most common cause for these symptoms after a new battery.
  • Faulty Battery Monitoring System (BMS) Sensor: The sensor on the negative battery cable can fail, giving incorrect readings.
  • Wiring/Connector Issues: Corroded or loose connections in the charging circuit.
  • Parasitic Draw: A module or accessory not shutting down correctly.

When to See a Shop: If you've performed basic checks and the issue persists, especially if you're not comfortable with electrical diagnostics or if an alternator replacement is needed, it's best to take it to a qualified Ford technician. They have specialized tools to diagnose the BMS and other complex electrical systems.

Safety Note: Always disconnect the negative battery terminal before working on electrical components to prevent accidental shorts or injury.

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