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Blink (a/k/a Flash) Codes – How to.

Blink (a/k/a Flash) Codes – How to.
While the preferred, and only complete, way to get diagnostic trouble codes (DTCs) from the car is to use a scan tool with Toyota-specific capabilities to query all of the electronic control units (ECUs) in the car, sometimes you have one or more warning light(s) showing and no good scan tool handy, and you still want to know what the trouble codes are.

When that happens, you have another option, for some, but not all, of the ECUs in the car: you can use a short piece of wire between two specific pins of the car's diagnostic port, and trigger some of those ECUs to use the warning lights they control on the dash to blink out their trouble codes, and you can count out the blinks to get two-digit codes.

(There's a similar way to get codes from the heat/air conditioning system, described toward the bottom of this page.)

This is a feature carried over from pre-OBD-II days, and the number of ECUs in the car that can do this trick has been decreasing over the Prius generations. In Gen 1, a lot of the car's ECUs could do it. In Gen 2, not as many, but still several, can do it. In Gen 3, it may just be down to the skid ECU (responsible for braking, stability, and traction control), the tire pressure monitor ECU, and the airbag ECU.

In all three of those early generations, the skid ECU is one of the ECUs capable of blinking codes. That's good news, because when there are warning lights from the brake system, it's always good to know what the codes are without delay.

Some of the description on this page assumes you are interested in codes from the skid ECU (the brake warning lights, or VSC or skid lights, are on). The same procedures apply to reading blink codes from other ECUs that can give them. It's just a matter of which dash lights you count the blinks of.

The skid ECU makes the most interesting example, because most other ECUs in the car might control just one warning light on the dash. For the airbag ECU, that's the airbag light, for example. But the skid ECU can blink more than one dash light. In Gen 3, for example, it controls the lights that say BRAKE, ABS, the VSC or skiddy-car traction light, and the ((!)) light (known as the ECB light, for electronically-controlled braking).

When trouble codes from the skid ECU are being blinked out, there can be codes blinking on more than one of those lights. Be sure to keep track of which codes flashed on which lights. Some of the two-digit code numbers overlap, and you need to know which ones blinked on which light to look up the right meanings in the repair manual.

To get started, you need nothing more than a short wire or paper clip. With the car turned off, short pins 4 and 13 on the OBD2 connector using the wire/clip, then put the car in IG-ON (press the POWER button twice with your foot off the brake).

After the first couple seconds, you might notice some lights blinking just a steady, fast, even on-off, like the drawing on the left below. That pattern is just telling you that ECU doesn't have any issues to tell you about.

Now observe the blinking patterns of whatever lights are blinking on the dash and not just steady fast on-off. Those lights are blinking codes for you, as in the drawing on the right. Every code is two digits.

If you see more than one light blinking codes, each light is blinking its own codes; don't try to figure out what they all mean at once. Focus on one of the lights at a time, ignore all the others, and note down what code or codes that one light is blinking.


If that light has multiple codes for you, they will blink out in ascending order. You know you have all the codes from that light when it wraps around and repeats one you noted down already. Then focus on the next light that's blinking codes, and note down all of those, and so on. Be sure to keep track of which codes were blinked on which light.

Once you have all your two-digit blink codes, you can look them up in the repair manual to see what full trouble codes they correspond to:

Toyota Service Information and Where To Find It | PriusChat

or post them in a question on PriusChat about your problem; some of the codes are familiar ones we've seen before.

In the repair manual, you will notice DTCs listed with the full five-character DTC, a slash, and then two digits. The two digits are the blink code. For example, C1345/66 is a code you'll see listed.

That gives you an easy way to look up most blink codes, if you have a searchable PDF of the manual (or even just of the section with the summary code tables in it). Just search for a slash followed by the blink code, like /66 and you'll probably land on the right code in just a few hits, if not the very first one.

But be careful to remember which light blinked which code. For brake codes, you might get hits in more than one table. For example, in the Gen 3 repair manual, there are tables named "ABS DTC", "VSC DTC", "Electronically Controlled Brake System DTC", and "ABS and Electronically Controlled Brake System DTC".

If you're searching for /66 for example, you will hit both C1290/66 in the "VSC DTC" table (a problem with the steering angle sensor) and C1345/66 in the "Electronically Controlled Brake System DTC" table (having to do with a valve offset the system needs to learn). So when you get your search hit, page back to the top of that table to see which table you're in, and make sure it's the right one for the light that blinked that code. If it isn't, try again with the next search hit.

There are a few blink codes you can't find that way, because there aren't real DTCs to go with them, so there's no slash where they're shown in the manual. They are:

  • On the ABS light:
    • 42: just means there are also codes on the ((!)) (ECB) light, go look at those.
  • On the VSC (skiddy-car) light:
    • 43: just means there are also codes on the ABS light, go look at those.
    • 45: just means there are also codes on the ((!)) (ECB) light, go look at those.
  • on the Electronically-Controlled Braking ((!)) light:
    • 36: just means there are also codes on the ABS light, go look at those.

There are a few brake system codes that come up often enough to be worth mentioning here:

  • 58 on the ((!)) ECB light is C1259, and 51 on the skiddy-car VSC light is C1310. Neither code means any problem with the brake system at all: they both tell you about some problem elsewhere in the car (in the hybrid powertrain control) that the brake system just needs to know about (because those systems cooperate to do regeneration). So these codes just mean you need to get the codes that really matter, from the ECUs controlling the hybrid system. (Sadly, that means you do need to arrange access to a scan tool, because those ECUs don't do blink codes.)
  • 41 on either the ABS or the ((!)) light is C1241 (remember the Gen 3 book has a fourth code table called "ABS and Electronically Controlled Brake System DTC"? That's the only code in it). It means a problem with the voltage arriving at the brake system's electrical connections. The problem can be anywhere along the wiring path bringing power there, but it wouldn't be crazy to start by checking the 12 volt battery. If no glaring problem there, then the repair manual has the rest of the troubleshooting steps.
  • 66 on the ((!)) ECB light is C1345, and it means the system wants to learn the right offset value for a certain valve in the actuator. There is a procedure where you can say "ok, go learn that" and it does, and there's even a version of the procedure that doesn't require a scan tool. See this post.
  • 72 on the ((!)) ECB light is C1451, and it means the system wants you to bleed the brakes. It really, really wants you to bleed the brakes. See this post. Sadly, this does mean you need access to a scan tool that can kick off the bleeding procedure.

This doesn't show historical codes, though. And again, only some of the ECUs in the car can do this. A scan tool like Techstream is needed to get trouble codes from the rest.

This Prius Wiki page has been created so that there is a convenient place to direct people, rather than regurgitate the same information over hundreds of posts.

The original thread (with thanks to Mr. F) from which this information was taken can be found here:

Check Hybrid System | Post #8 |PriusChat

About clearing codes

While in this code-blinking mode, some ECUs will also allow you to clear their codes by some specific action. For example, the ECU controlling brakes and skid will clear the codes if you press the brake pedal a specific number of times. Naturally, the idea is that you note down what trouble codes are being blinked before you clear them.

For some reason, ludicrous numbers of people on PriusChat have only ever heard of this method as a way to blindly clear codes, without even realizing that it also tells you what the codes are. New posts are made again and again with some variant or other on "I don't know what the codes are, but I cleared them with the pin trick." So every one of those posters has been right here using this method and not even noticed what was being blinked out, and just blindly cleared the information that would have explained the warning in their car.

If you've read this far, you know better than to make a post like that.

"When I clear the codes, everything is fine."

Some people notice that they can't tell anything is wrong with the car until the warning lights come on, and then it seems to work differently. They clear the codes and it goes back to working as it did before, until the lights come on again. People make funny assumptions about what that means, such as that nothing is really wrong with the car and the codes are being triggered in error.

Avoid that mistake. Most codes are designed to warn you of a problem developing before it would be obvious to the driver. That's what makes it a warning. It would be less useful to have codes only for problems you already can tell you have.

Also, for many codes, the ECU will be programmed so if the code is reported, the ECU will change the car's behavior in some way to protect you and the car. That different behavior is what you notice when the problem is reported, and what you notice going back to normal if you clear the report. That does not prove there's really nothing wrong with the car. It only proves that you can defeat the protective measures by making the car forget it found a problem.

Codes from the heat/air conditioning system

In some generations at least, you can also get trouble codes from the heating/air conditioning system without a scan tool. In the Gen 1 Prius, the non-scan-tool way was the only way (that HVAC system didn't talk to any scan tool). In Gen 2 and Gen 3, you can either use a scan tool or the non-scan-tool method. I don't know the details for generations after 3.

  • Gen 1: start with the key off, and turn the fan knob to off. Turn the car key on, press the A/C button three times, then turn the fan knob to AUTO. All the HVAC indicator lights will blink a few times together, then the A/C button light will blink out two-digit codes. Count those and read them the same way as described earlier on this page.
  • Gen 2: Start with the car off. Hold down both the A/C AUTO and FRESH/RECIRC buttons (on the steering wheel), while turning the car on (two power button presses, no foot on brake). Look for two-digit codes shown in the top corner of the MFD. The two-digit code xy usually means the same as a B14xy code shown on a scan tool.
  • Gen 3: Start with the car off. Hold down both the A/C AUTO and FRESH/RECIRC buttons, while turning the car on (two power button presses, no foot on brake). Look for two-digit codes shown at the left end of the HVAC display. The two-digit code xy usually means the same as a B14xy code shown on a scan tool.

B1421 (blink code 21) from the heat/air conditioning system

People see this code a lot. It is only provided as a way to know whether the solar sensor on the dash is working. If you read codes from the HVAC when strong sunlight is falling on the dash, you should not have this code. If you read the codes while strong light isn't falling there, you should have this code. That's normal and does not indicate any problem.

The only time it would indicate a problem would be if you did have this code in strong light, or if you did not have it in the dark.
Jan 25, 2024
Sarah Brady, zfk110 and Mr. F like this.