ABS and Brake Light Codes C1251 and C1256

I would get a can of the brake fluid and top off the reservoir and repeat the test. I remember our old 03 Prius was sensitive about brake fluid level. BUT we don't own one any longer and memories being what they are.

I also remember that using a non-ISO-9141 code reader could induce false brake errors. The problem was testing for CAN bus access, in the NHW11 one of those lines is used for brake controller communications. Until the CAN bus lines were isolated or the code reader set to do ISO-9141 only, 3d party code readers could induce false brake errors.

So do you have your own jack stands? I would want to inspect the front brake pads and rear brake shoes to make sure everything is OK. As these wear down, it can lower the brake fluid and lead to low-fluid level.

GOOD LUCK!
Bob Wilson

 

What Toyota manual are you talking about? My Gen 1 manual does not associate either code with the actuator (which is the big Medusa-like thing near the middle of the firewall).

In my manual, the table on page DI-359 associates C1251 specifically with the accumulator pump motor, while C1256 leaves a bit more to pin down, possibly involving the motor, either pressure switch, or the accumulator itself; all of these are parts of the accumulator assembly, which is way over on the passenger side, buried under the brake fluid reservoir.

For the lowdown on C1251, you turn to page DI-406 and follow the instructions (3 pages) to pinpoint the problem; for C1256 you turn to DI-424 and follow the six pages there. (In each section, the first page starts with a little table that tells you exactly what conditions the computer measures that lead it to set that code. That's useful to know even if you don't follow the whole step-by-step to pinpoint the problem.)

My page numbers are in the 2001 paper edition, they might not be exactly the same for 2003, and if you're viewing on techinfo I am not sure there are page numbers at all, but you should be able to find the same sections.

Some minor things might have changed between '01 and '03, but I'm pretty sure they didn't change two trouble codes that meant the accumulator in '01 to mean the actuator in '03. I'm very curious about what "Toyota manual" would have said that.

-Chap

 

If I'd offered to pay you to demonstrate the dangers of random web searching for repair information, this would have earned payment in full.

Those two excerpts are clearly from different manuals (one has numbered chapters, one has two-letter coded chapters like BC). The second one at least has a footer identifying it as a preliminary release for a 2004 (gen 2) Prius. The first one doesn't identify the car model, year, or even the make. Graphically, it does look like it's probably a Toyota, Scion, or Lexus manual for some car model that uses an ABS motor, but that's about all I can get from it.

If you're driving a 2003 Prius, neither one of those is for your car. You can see that the basic meanings of the codes haven't changed (C1251 is about the pump motor, C1256 is about the low-pressure sensor), but the instructions on what to change out are different from what you would find in the 2003 Prius manual.

Why would they be different? Well, the first sentence of that C1256 excerpt gives a hint: "The accumulator pressure sensor is built into the actuator...." So in a 2004 Prius, the actuator is what you would replace if that sensor had gone bad. In a 2003, the sensor isn't built into the actuator. It's built into the accumulator assembly, mounted separately over on the passenger end of the firewall. Looking in a 2003 Prius manual, you would clearly see that.

Likewise, in that C1251 excerpt, though it doesn't come right out and say it, we can infer the pump motor is part of the "ABS and traction actuator assembly" in whatever kind of car that excerpt happens to be about. That's just not where it is in a 2003 Prius though.

I hope that helps, and this thread will probably also help future readers who need a good example of why searching for manual bits on the web isn't always the same as looking them up on techinfo where you know you're getting the manual for your car, model, and year.

-Chap

 

I'm sorry it came across as rude or snide. It was meant sincerely. You didn't trust the information you were finding, and you were right not to trust it, because you were finding the wrong information. That's an inherent danger in using unfocused internet searches to look up diagnostic code information for other models and years of car and trying to apply it to your own car, which is not built the same way. If you had gone to the repair manual for your 2003 Prius, you would have found the information you need, and you would be able to trust it.

You seemed to be wondering why the information you were getting was puzzling, and that's why.

Meanwhile, with this version of your original question ...

... you're getting colder. The correct information in your Gen 1 manual will direct you to the accumulator assembly (passenger side, firewall, beneath brake fluid reservoir). It will not direct you to the actuator assembly (Medusa-like thing mid-firewall); that was a red herring from one mechanic and manuals for other cars. And nothing at all has directed you to the booster, which in Gen 1 is integrated into the master cylinder.

Some people do confuse accumulator and booster, but sticking to Toyota's nomenclature is another key to avoiding confusion on an issue like this.

In other words, you are likely to end up replacing the accumulator. I'd recommend you not jump into it on my say-so, but after confirming it to your own satisfaction by following the checks in the actual 2003 Prius manual. But you are likely to end up there when you do. There is a PriusChat member, rlin78, who found that it's possible to replace it without having to evacuate and recharge the A/C, if you have about ten hours to spend on it. That thread should come up in a forum search.

I'm sorry my phrasing put you off so strongly that you didn't notice the answers to your question were in the post. But here's what I was trying to get at. You aren't the first person on PriusChat, and you won't be the last, to show up with a question that's all turned around because of information gathered from an unfocused internet search that pulled up stuff about different cars than the one you've got.

It's hard to write good made-up examples to show people exactly how that approach can lead to confusion and delay (or worse) in solving an issue. You've supplied a really good, real-life example, that other readers will understand. That is not a knock on you in any way, and by supplying such an example (even inadvertently), you will have helped people here. I mean that sincerely, and that's what I was trying to say.

I'm sorry I said it poorly.

-Chap

 

You have nothing to apologize for Mr. Chapman. Your knowledge and insight has been invaluable to many of us. This snowflake is is demanding something for nothing and shouldn't be given the time of day after his "complaint". It just shows your class that you continued to help him after his outburst. Guys like you on these forums deserve better. Thanks for all your help.

 

Where in AZ are you? I ask because there are two gen 1 priuses at the local Pull a Part yard in Tucson. And the motor, pump, and accumulator are still likely available. I replaced the one on my 02 and total cost was about $25. Plus a bunch of brake fluid. It's all one assembly btw and not impossible to remove. My 02 had the warning lites and the high pitched squeal, and in addition a very unresponsive brake pedal. Bench testing it, the motor turned out to be dead.

There are also several Gen 1's in the Phoenix area, check Craigslist, for the details.

I used the HF air powered vacuum bleeder and the brakes are now okay.