The Lemon IndexOn Toyota and Lexus models with a powered brake booster (mostly hybrids), the brake computer saw the stored brake pressure falling faster than it should, which points to an internal leak. Full C1391 page
210 owner complaints · the #1 code Toyota Prius owners name · 69% of Toyota Prius complaints that name a code (every car: 2.4%)
Middle of 137,000 miles · most between 104,000 and 163,000 (41 owners gave it)
Toyota Prius owners named C1391 in 210 complaints to the U.S. government (NHTSA), most often on the 2010, 2013 and 2011 model years, at a middle of 137,000 miles. The part they name most is the ABS module, pump or accumulator (114 complaints). Complaints are owner reports, not proof of a defect.
Toyota Prius model years that report C1391
Owner complaints naming C1391, by model year. Raw counts: years that sold more get more complaints, so this is each model year's record, not a failure rate.
Mileage when it happened
137,000 miles is the middle of what 41 owners entered. Half were between 104,000 and 163,000 miles.
The mileage on the complaint form, when the owner gave one.
What owners say caused it or fixed it
The most-named part is the ABS module, pump or accumulator, in 114 of the 210 complaints (54%). 41 of those mention it being replaced or repaired, and 7 say the problem came back afterwards. Next: engine software (a reflash) (3).
- ABS module, pump or brake accumulator114 complaints41 mention a repair or replacement, 7 of them say the problem came back · what Toyota Prius owners paid
- Software update (reflash)3 complaints3 mention a repair or replacement, 1 of them says the problem came back
89 complaints mention a recall and 63 mention a warranty.
Counted from the owners' own words: a part counts when a sentence names it with a cause or repair word. What owners wrote, not a diagnosis. A shop should confirm the cause before replacing parts.
Symptoms owners describe with C1391
2% of these complaints say the check engine light came on.
- Brakes or ABS act up98%206 of 210 complaints
- Warning lights and electrical faults33%70 of 210 complaints
- Transmission slips or shifts hard8%16 of 210 complaints
- Loses power or goes into limp mode1%3 of 210 complaints
Share of the complaints naming C1391 whose text also describes each problem. A complaint can describe more than one.
Codes owners report with it
C1256 20 C1252 8 C1253 7 C1241 3 U0293 2
Other codes named in the same Toyota Prius complaints, and in how many.
Repair costs
- Brake booster replacement$2,8006 bills · middle bill
- Brake repair$2,8194 bills · middle bill
- ABS module replacement$3,0003 bills · middle bill
- Brake master cylinder replacement$3,3003 bills · middle bill
- ECM (engine computer) replacement$4,4001 bill
Repair bills owners named in these 210 complaints (17 in all). Owner reports, not a quote: costs vary by shop and region.
Recalls on these Toyota Prius years
- Brakes · 2010 · issued 2013
Nitrogen gas from a component of the brake booster pump assembly could leak into the brake fluid. NHTSA 13V235000 - Service brakes, air · 2010 · issued 2010
TOYOTA IS RECALLING CERTAIN MODEL YEAR 2010 TOYOTA PRIUS AND LEXUS HS250H PASSENGER VEHICLES. NHTSA 10V039000
2 recalls for the same systems (brakes) on the Toyota Prius model years above. A recall for the same system isn't proof it's behind C1391. Recall work is free at any dealer: check a VIN at nhtsa.gov/recalls or with our VIN check.
Keep going
- C1391: meaning, causes and every car that reports it
- Toyota Prius reliability by year
- 2010 Toyota Prius problems and recalls
Other codes Toyota Prius owners report
C1391 on other cars
Toyota Highlander (49) · Toyota Camry (20)
The details
How we count
We read every owner complaint in the NHTSA file whose text names this trouble code, and count the ones filed about this model (matched by the make, model and model year on the complaint). Mileage is what the owner entered on the form.
Parts: a complaint counts for a part when one of the owner's own sentences names that part together with a cause word (failed, bad, diagnosed, caused by, leaking ...) or a repair word (replaced, repaired, new, reprogrammed ...). "Came back" means the same complaint also says the problem returned or the repair didn't fix it. These are counts of what owners wrote, not a diagnosis, and one complaint can name several parts.
Complaints are reports, not proof of a defect, and most owners never file one. Popular models get more complaints, so the counts are not a failure rate. The code meaning is the standard SAE J2012 definition in our own words, or the carmaker's meaning where we verified it for that make.
What C1391 means
On Toyota and Lexus models with a powered brake booster (mostly hybrids), the brake computer saw the stored brake pressure falling faster than it should, which points to an internal leak. Braking assist can be affected, so get it checked before driving much.
Stop and fix now. Don't put it off. This can affect safety, stall the car or cause expensive damage.
- Internal leak in the brake booster/accumulator assembly
- Leaking seals in the brake actuator
Check the complaints yourself
NHTSA complaint numbers (search them at nhtsa.gov): 11777065, 11775030, 11772247, 11770551, 11768253, 11768168, 11765138, 11762180, 11760825, 11759804, 11759367, 11756229 and 198 more.
Quick answers
What does C1391 mean on a Toyota Prius?
Abnormal Leak in Brake Accumulator. On Toyota and Lexus models with a powered brake booster (mostly hybrids), the brake computer saw the stored brake pressure falling faster than it should, which points to an internal leak. Braking assist can be affected, so get it checked before driving much.
Which Toyota Prius years have the most C1391 complaints?
In complaints to NHTSA, owners of the 2010 (61), 2013 (42), 2011 (30) Toyota Prius named C1391 most (210 complaints in all, 2004–2015). Raw counts, not a failure rate.
What fixes C1391 on a Toyota Prius?
Owners most often name the ABS module, pump or accumulator (114 of 210 complaints), then engine software (a reflash). That's what owners wrote, not a diagnosis: have a shop confirm the cause with a scan and tests before replacing parts.
At what mileage does C1391 show up on a Toyota Prius?
Owners who gave their mileage reported a middle of 137,000 miles; half were between 104,000 and 163,000 (41 owners).
Can I drive my Toyota Prius with C1391?
Stop and fix now. Don't put it off. This can affect safety, stall the car or cause expensive damage.
Sources: NHTSA owner complaints that name C1391 on the Toyota Prius, counted by The Lemon Index; NHTSA recalls; repair bills owners named. Meanings: SAE J2012 in our own words. Owner reports, not a diagnosis or repair advice for your car.