Brake problems?

Today my wife called because the car had the brake light lit and an alarm was sounding. This started when she was waiting, with the foot on the brake, in a long traffic light. It continued for about ten miles when she stopped to call me, after that the alarm stopped and she could drive home without any other issue. At no moment she felt that there was something different with the brakes or the car.

I checked the car and I noticed that if I keep pushing (without pumping) the brake pedal starts to move like it's loosing pressure, if I wait enough it gets to the bottom. Is this normal? Once I release the brake pedal, the car makes a loud pump noise and the pressure comes back. If I pump the brakes the alarm comes off, but I think this is normal.

I checked the brake fluid and it is full (a bit more than the maximum, actually).

Looking up for the VIN there doesn't seem to be an open recall for my car, I don't know if this mean that it was already repaired or it never had the issue (by the VIN number it seems it should have been recalled).

IIRC we've only had one (unconfirmed) brake issue on this forum. Your 2014 i-MiEV with around 8000 miles should be fully covered under warranty. I'd get it to a Mitsu dealer right away. Do let us know what they say/do. I'm holding off speculating...

Brakes are conventional hydraulics + an electric vacuum pump. Unlikely to be any issues with the hydraulics @ 8K miles so possible vacuum leak is most likely or pump issue.

There was a recall to change the brake vacuum pump on the 2012 cars just to prevent this problem - Don't think that recall applies to your car. It does sound like you may have a vacuum issue though - First instance of this we've heard of, if that's the case. Whatever, let the dealer sort it out for you

Don

restrict said:

I checked the car and I noticed that if I keep pushing (without pumping) the brake pedal starts to move like it's loosing pressure, if I wait enough it gets to the bottom. Is this normal? Once I release the brake pedal, the car makes a loud pump noise and the pressure comes back. If I pump the brakes the alarm comes off, but I think this is normal.

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Do you mean that holding pressure on the brake pedal causes it to slowly sink to the floor? If so, that's not normal. It should be almost impossible to bottom the pedal out.

Yes, you need to get the car in for service. The brakes are very conventional on the I-MiEV, so they should act like conventional brakes. They are vacuum assisted power disc/drum brakes and are not connected in any way to the EV system. The EV regen system is actuated through a sensor that measures brake pedal movement to control the amount of regen. Nothing is involved in the hydraulic system. My opinion is that without the loss of any brake fluid, the fluid must be bypassing something to allow the pedal to move and finally go to the floor. The only place this could be happening is the master cylinder as anything else in the system (brake calipers, wheel cylinders, ABS pump, etc.) would cause either a fluid loss or system (ABS) malfunction, not a pedal slowly moving to the floor. However, even with an internally leaking master cylinder, because this is a two circuit system, it is unusual that the pedal would go fully to the floor. I might go almost all the way to the floor but one of the two circuits should be able to provide limited braking. The thing to look for is brake adjustment of the rear drums after you fix the initial problem. Disc brakes self adjust, drums should but sometimes do not. If you had a fluid bypass in the master cylinder section that applies the disc (front) brakes and the rear (drum) brakes were out of adjustment, then you could get the pedal to the floor before any of the brakes were fully applied. A quick check of how far you have to pull the handbrake lever until the parking brake applies is an indication of the condition and adjustment of the rear drum brakes. This applies to every I-MiEV owner (or for that matter anybody that drives a car with rear drum brakes). Most drum brakes are self adjusting by a little lever that moves the adjuster each time you apply the brakes while stopping in reverse. These adjusters are located inside the brake and can fail for a number of reasons. If you need to pull the hand brake lever more than a few notches to make the parking brake work, this is a sure sign of an adjustment or wear issue in the drum brake that needs to be looked at and corrected. A few cars do not have self adjusting brakes and rely on the adjustment of the parking brake cables to set the proper clearance of the shoes to the drum. I can't remember if this is the case with the I-Miev or not.

BTW--even though I proofread this a couple of times I am not responsible if I used the word "break" instead of "brake" in writing this !

Edit: Just checked the service manual. The brake adjusters in the I-MiEV are actuated by the parking brake lever operation. So if you never use the parking brake, you never adjust the brakes. The manual spec is with a 45 pound pull on the parking brake lever, the lever should move six to seven notches (clicks) before you reach the 45 pound limit. There is an adjustment for the cable located in the center console to set this. However, I would manually rotate the adjusters instead of adjusting the cables if this is a problem. If you go the easy route, you are adjusting something (cable length) to correct another problem (lack of using the handbrake) to fix it. IMO, the repeated application of the parking brake handle should bring the shoe/drum clearance into spec if the adjusters are not stuck from non use. If this doesn't work, you need to pull the rear wheels and drums to physically adjust the brakes and clean all the crud out.

PV1 said:

Do you mean that holding pressure on the brake pedal causes it to slowly sink to the floor? If so, that's not normal. It should be almost impossible to bottom the pedal out.

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Yes, precisely that. In a normal car that would mean there is something wrong with the brakes, but I wasn't sure whether somehow that was normal on the i-Miev's brake system.

Thanks everybody for the comments, I will take the car to the dealer to have the brakes checked. I will let you know how it goes.

i'm gonna guess there is air in the system that needs to be bled out, and it's probably not real easy to do with ABS brakes.

Resisting Joe's resistance to speculation, I'll wager that since there's a "loud pump noise", that would be the ABS pulsator rather than the vacuum pump. Easy to narrow down, as the ABS motor is in front and the vac pump out back. ABS pulsator would also be felt in the pedal.
BUT, if the vac pump got corroded by salt through the outlet, per our recall, it could get noisier and leaky.

jray3 said:

Resisting Joe's resistance to speculation, I'll wager that since there's a "loud pump noise", that would be the ABS pulsator rather than the vacuum pump. Easy to narrow down, as the ABS motor is in front and the vac pump out back. ABS pulsator would also be felt in the pedal.
BUT, if the vac pump got corroded by salt through the outlet, per our recall, it could get noisier and leaky.

Click to expand...

I would have recognized it if it was the ABS, this is a loud noise from a pump when I release the brake pedal. Is there a way to inspect the brake pump?

I checked the service record for my car, and it says "IMIEV BRAKE VACUUM PUMP - REFLASH ONLY". So it was recalled but they only changed the software, and not the pump.

Is this the sound you hear (may need to crank up the volume)?

https://www.youtube.com/watch?v=ZNxcDcLgWV0

Yes, that is the sound.

Just a note---The vacuum pump may be bad on the OP's vehicle. However, if it failed the only problem would be loss of power assist to the brake system. Although that is alarming and requires more pedal effort to stop the car, it wouldn't explain the fact that the OP's brake pedal will eventually go all the way to the floor if constant pressure is applied. Most likely, the vacuum pump needs replacement. As most of you owners know, the vacuum pump has been an issue on the I-MiEV from the original model that overheated to the re-flash of the software controlling the newer pumps. I also feel the pump location in the motor compartment wasn't the best choice for durability of the pump but was made for noise and vibration considerations. The bottom line is----there is another possible problem with the hydraulic brake system on the OP's car that might not have been detected without the vacuum pump issue. And after looking at how the rear brake self adjusters work by use of the hand brake lever, I would suggest all on this forum check for the 6 to 7 click movement of the lever to apply the parking brake to assure the rear brakes are working properly. If it is out of spec, it needs to be fixed. If the adjusters are still working, use of the parking brake lever from time to time should bring the brakes into adjustment without further maintenance--just keep an eye on it.

BTW--any of you that are old enough or have been in this EV thing long enough are probably wondering how the I-MiEV vacuum pump even lasted for a year. Early on, if you needed a vacuum pump for a conversion, they were hard to find in 12 volt--sometimes a cheap tire inflator compressor modified for vacuum. Always the noisiest thing in the car and (at least for me) the first thing to not turn on when needed or not turn off when not needed .

If there isn't any fluid leaking, I'd check the rear drum brakes for proper adjustment (as Siai47 pointed out), but if they are fine, then the master cylinder may need replaced. For the pedal to sink, something is causing a loss of pressure in the hydraulic system.

A malfunctioning vacuum pump would cause the exact opposite behavior where the pedal doesn't want to depress. But even with the loss of vacuum assist, pressing the brake pedal with both feet and putting the car in B mode still offers plenty of braking power. If nothing else, Reverse will electrically stop forward motion once the car falls below 6 MPH (just don't engage Park while moving as you'll either break the parking pawl or your nose from hitting the steering wheel :x ).

(Regarding vacuum pumps, GM got around that by using electric trailer brakes in the EV1.)

PV1 said:

If there isn't any fluid leaking, I'd check the rear drum brakes for proper adjustment (as Siai47 pointed out), but if they are fine, then the master cylinder may need replaced. For the pedal to sink, something is causing a loss of pressure in the hydraulic system.

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This is the strange thing, there seem to be two independent issues. I haven't had time to take the car to the dealer yet (too many things to do and the closest dealer is not that close), but somehow the brake pedal does not seem to sink as fast as it did the other day.

I took the car to the dealer today, they just called me and said that the brake vacuum pump needs to be replaced. They will have it ready tomorrow.