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Vehicle engine and/or automatic transmission

Code: P0628 - The control circuit for Fuel Pump "A" has low voltage, which may affect how the fuel pump works.

When you see a P0628 code, your vehicle’s computer is telling you there’s a low voltage problem in the "Fuel Pump Control Circuit A." Let me put that into plain talk from years on the garage floor: the signal that controls your fuel pump’s on-off cycle just isn’t making it through like it should, almost always because something’s gone sideways in the wiring or connectors. This isn’t a brand-specific headache-Ford, Toyota, Chevy, Nissan, you name it, I’ve seen it on all of them. The fuel pump’s job is straightforward but vital: getting gas from the tank to your engine. If that control circuit is out of whack, your pump could fail to run when you need it, or worse, quit while you’re driving. The system handling this job might be the main computer (PCM or ECM), sometimes a separate fuel pump module, or even other controllers depending on your ride. Here’s the bottom line from the toolbox: if this circuit isn’t doing its job, your engine’s not getting the fuel it needs, and that means trouble.

Causes of P0628 engine code

From my time under the hood, I can tell you that P0628 almost always traces back to electrical gremlins. Here’s what I see most often causing the issue:

The fuel pump itself is on its last legs or has already failed.
A ground wire at the fuel pump module is broken, loose, or corroded.
The ground strap at the control module isn’t tight or has come off.
Wiring in the fuel pump circuit (or even the CAN bus) is damaged, corroded, or just not making a good connection anymore.
CAN bus problems-less frequent, but they do crop up and can drive you nuts.
Wire harnesses that aren’t secured properly can rub against metal and eventually break, killing the circuit.
Melted, corroded connectors or wires with internal corrosion can add resistance that throws off the voltage.

In my experience, the vast majority of these cases come down to bad wiring or connectors, especially on vehicles that see winter salt or lots of wet weather. Always check those first before you start swapping out expensive parts.

Symptoms of P0628 code

When P0628 shows up, you’ll usually get some pretty clear signals from your car. Here’s what I’ve heard from customers and seen myself:

That check engine light is almost always glowing.
The engine will crank and crank, but just won’t catch-or it might start and then stall a few seconds later.
Rough idle or misfires, especially when you’re asking for more power going uphill or merging on the highway.
Your gas mileage drops off, sometimes sharply.
It’s not uncommon for the engine to die once it gets warm, then refuse to restart until it cools off.
Sometimes, everything seems fine after a cold start, but the car refuses to restart after a quick trip to the store.

Bottom line: anything that interrupts the fuel flow can leave your engine sputtering or, worse, leave you stranded at the worst possible moment.

Diagnosis with obd code P0628

When I’m diagnosing a P0628, here’s the routine I stick to:

First thing, I hunt down any Technical Service Bulletins (TSBs) for your specific make and model. Sometimes, the automaker has already figured out the fix and you can save yourself a lot of chasing.
Next up, I use a reliable OBD-II scanner to check every module for codes. This gives the full story, not just what’s going on with the fuel pump.
Then, it’s time to pop the hood and eyeball the wiring and connectors around the fuel tank and fuel pump. Look for obvious stuff: worn insulation, loose plugs, green crusty corrosion. These areas take a beating from the road.
After that, I focus on all the ground points. A weak ground is a classic troublemaker. I’ll add a jumper wire as a temporary ground-if everything suddenly works, you’ve found your culprit. Clean off any corrosion and make sure those grounds are tight.
Next, I grab a wiring diagram and start tracing the fuel pump control circuit, checking for continuity with a multimeter. Find a broken wire or short? Cut it out and replace with fresh wire, solder, and heat-shrink tubing. That’s how you keep moisture out and the repair solid.
If the wiring checks out, I’ll test for voltage at the fuel pump connector while a helper cranks the engine. No voltage? The problem is upstream. If you’ve got voltage but the pump’s silent, odds are the pump itself is toast.

Here’s a pro-tip from the garage: have a buddy help out, especially when you need to crank the engine or crawl under the car. And always disconnect your battery before poking around fuel system wiring-sparks and gasoline don’t mix.

Common Mistakes with dtc P0628

I’ve seen folks throw money and time away chasing this code. A classic mistake is rushing to replace the fuel pump before checking the wiring and grounds-don’t fall into that trap. Another one is missing corroded or loose connectors, especially those hidden on top of the fuel tank where you don’t want to look. Skipping TSBs is another time-waster; sometimes the fix is staring you in the face if you just check. And don’t forget about the CAN bus-if everything else looks good, a wiring fault there can mimic a fuel pump problem and send you on a wild goose chase.

Seriousness of obd2 code P0628

You really can’t afford to ignore a P0628. Sure, you might limp it around for a while, but there’s a real risk your engine could suddenly lose power and leave you dead in the water-think highway traffic, intersections, you name it. That’s not just annoying, it’s downright dangerous. On top of that, running your engine with an unstable fuel flow can cause misfires that eventually damage the engine. The potential casualties? Fuel pump, wiring harness, connectors, and if things get really bad, the engine itself from running too lean or stalling repeatedly. My advice: don’t wait. Get on top of this before it turns a minor headache into a major repair bill.

Repair steps for P0628

This is my go-to checklist when fixing a P0628:

Track down and repair or replace any damaged wires or connectors in the fuel pump circuit.
Clean and snug up all ground connections, especially at the pump and any control modules.
If voltage and continuity tests say the pump’s a goner, swap it out for a new one.
If you find CAN bus wiring issues, sort those out-don’t ignore them.
And always, always follow any TSBs for your vehicle; sometimes a software update or a new part from the dealer is the real fix.

One more tip: use quality parts and make sure your repairs are sealed up tight against moisture. Under-car wiring lives a hard life, and a sloppy fix won’t last long.

Conclusion

If you’re seeing P0628, it’s telling you your fuel pump control circuit isn’t getting the voltage it needs-most likely because of a wiring or ground issue. You could be facing hard starts, sudden stalls, or that ever-annoying check engine light. Don’t brush it off; this is one of those codes that can strand you or do real engine damage if you let it slide. My advice? Start with the basics: check your wiring and grounds, look up TSBs, and only go for the pump replacement once you’ve ruled everything else out. Work methodically, and you’ll get your car back to running right-and you’ll save yourself a lot of frustration along the way.

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