A 2007 Prius with 179,000 miles died while driving. The owner called a mobile hybrid battery company, who came out and replaced the high-voltage battery. After the install, the car would ready up but die after a few seconds. The customer added four gallons of fuel thinking it might be empty. Still wouldn’t start. The car got towed to us on a referral from another shop up in Hood River.
What we found
We scanned the car and found no codes in the PCM at all. The HV system had P0A80 (replace HV battery), but the freeze frame showed the battery modules were very low from all the failed start attempts, not from the battery itself being bad.
We verified the fuel pump was working and pulled the spark plugs. They were fouled in a way that didn’t look normal. Then we took a fuel sample. It didn’t smell like gasoline. It didn’t feel like gasoline. And when we tested it, it didn’t burn like gasoline.
The fuel was contaminated. We drained nearly ten gallons of bad fuel from the tank.
But the damage was already compounding. After adding five gallons of fresh gas and clearing codes, the car still wouldn’t crank. All those failed start attempts (before it arrived, and during the mobile battery install) had drained the brand-new HV battery down to nearly zero. Module voltage was under 12 volts with a state of charge at zero. The battery was so deeply discharged it couldn’t turn the engine over.
The customer approved a second HV battery replacement. After the new battery and fresh fuel, the car started. But now there was a cylinder one misfire. We cleaned the fouled aftermarket spark plugs, swapped the coil to a different cylinder to rule it out, and the misfire stayed on cylinder one. We ended up replacing all the spark plugs, cleaning the fuel injectors and fuel rail, and clearing codes.
After a test drive on the freeway and surface streets, the car was running clean with no codes.
The fix
Drained contaminated fuel, replaced the HV battery (again), replaced spark plugs, cleaned fuel injectors and rail. Multiple layers of repair because the root cause (bad fuel) had created a chain of secondary failures.
What this means for you
The mobile battery company solved the wrong problem. The original HV battery was probably fine. The car died because it was running on contaminated fuel, and when the engine can’t run, a hybrid’s HV battery drains fast from repeated start attempts.
This is an expensive lesson in diagnosis order. If the mobile installer had checked fuel quality first, the customer might have gotten away with a fuel drain and fresh gas. Instead, they paid for a battery they didn’t need, which then got destroyed by the continued cranking attempts, plus a second battery, plugs, and injector service.
If your Prius dies while driving and won’t restart, don’t keep cranking it. Every failed start attempt drains the HV battery further. And before anyone replaces your hybrid battery, make sure the basics are covered: is there fuel? Is it good fuel? Is the fuel pump working? A $5,000 hybrid battery doesn’t fix a $200 fuel problem.