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Error Codes P0620 and P1000 in 2007 Ford F-150 5.4L Flex Fuel: Charging System Diagnosis and Fixes

Model: 2007 Ford F-150 Fault Code: P0620 Posted: 2016-02-28 14:22

I own a 2007 Ford F-150 XLT with a 5.4L flex fuel engine, and I've been experiencing persistent error codes P0620 and P1000 for approximately three weeks. The issue began when I noticed the battery light flickering on and off while driving—sometimes staying off briefly, then reactivating. I visited two different auto parts stores to have it diagnosed. One reported a weak battery but confirmed it was in good condition; another said the alternator was faulty, while the other claimed it was fine. I replaced the alternator myself based on this uncertainty, but the problem persists. To troubleshoot further, I installed two voltmeters at the battery terminals and observed that the charging system would take several miles of driving to stabilize. Once stable, the voltage reached around 14.1 volts, and the dashboard gauge remained in its normal range. After driving about 50 miles, I checked the battery voltage in the garage and found it was approximately 12.8 volts. A friend with a code reader confirmed the presence of P0620 (Alternator Output Voltage Too Low) and P1000 (Charging System Malfunction). When I removed the alternator for testing, it failed three consecutive bench tests—showing inconsistent output between 13.1 and 13.5 volts under load. I replaced the alternator with a new one from the store, but the issue remains. The battery light still flickers intermittently, and the charging system appears unstable. I'm seeking advice on what other components might be at fault or whether there's a deeper electronic issue related to the Powertrain Control Module (PCM) that could be causing these error codes. I appreciate any insights into potential causes—especially for this specific 2007 F-150 model with flex fuel capability. Thanks in advance!

Related fault codes

P0620P1000

Comments (8)

Anonymous 2016-02-28 15:14

Added a detail: I removed the negative battery cable while the engine was running, and the truck continued to run without issues. Also, one of the parts stores replaced my two-year-old battery (it's actually five years old) thinking it might be faulty, but their tester showed it as good.

Anonymous 2016-02-29 07:44

A properly functioning alternator should produce between 13.5 and 14.5 volts under load. The intermittent battery light and low voltage readings suggest a charging system issue involving the alternator, wiring, voltage regulator, or fusible links. It's critical to have a qualified technician perform a full charging system diagnostic—including all components—rather than relying on isolated tests.

Anonymous 2016-02-29 08:35

Thanks Mohawkmtrs—I was planning to visit a shop next, but I'm hoping to avoid paying for extensive repairs without clear diagnosis.

Anonymous 2016-03-07 08:52

Problem resolved. After taking the truck to a repair shop, they diagnosed and replaced the PCM, alternator, drive belt, and belt adjustment pulley. Total cost: $1,800. This was a comprehensive fix that addressed both error codes and intermittent charging issues.

Anonymous 2016-03-08 07:33

Thanks for sharing your resolution—it helps others understand the full scope of what can happen with these error codes in older F-150 models.

Anonymous 2019-05-15 17:23

I'm experiencing a very similar issue on my 2004 Ford Expedition. I did not disconnect the negative battery cable while running, but I've observed that when the 'check charging system' warning appears and stays active for long periods, the battery drains noticeably. Otherwise, once the warning flickers briefly, the alternator seems to recharge the battery. I'm scheduling a professional inspection of both battery and alternator tonight. The alternator reads 14.5 volts, and the battery consistently shows 12.55 volts. I’m concerned about overpaying for repairs that rely on trial-and-error methods—will update once results are known.

Anonymous 2021-05-09 23:50

I'm having the same issue with my 2003 Ford Expedition. We've tested the alternator and replaced the battery, but the charging system remains unstable. Any suggestions on what else to check or where to look for root causes?

Anonymous 2021-05-09 23:51

cspur wrote: Wed May 15, 2019 5:23 pm I am dealing almost the exact same issue on my 2004 Ford Expedition, except I didn't remove the negative battery cable while the engine was running. I'm going to have battery and alternator professionally checked this evening. The alt is putting out 14.5 volts and the battery is consistently 12.55 volts. The exception being that the battery becomes drained somewhat after one of these instances where the "check charging system" alert comes on and stays on too long. Otherwise, it seems the alternator is able to recharge the battery if the warning is intermittent enough. I don't want to pay $1800 to fix mine by what sounds like the repair facility was using trial and error to find the real problem. I will let you know how it turns out. Did you ever figure out the root cause of your issue?