s14 200sx ABS HELP

[RocketScienceRacing]

Guys, can anyone help me with this problem that I'm having with my S14. I have seen this same problem on another S14. The problem is sometimes when the brake is applied the pedel becomes very hard, and there is absolutely no brakes, then the ABS warning light comes on and the pedal becomes soft and the pedal sinks to the floor then the brakes lock up until you release the pedal. At that point the car is in non ABS mode, and the ABS warning light is on, a check of the lights gives code 77, and a check with a consult 3 says control unit 4, but no other explination. Does anyone know what Control Unit 4 is? Code 77 says Control Unit/Ground Curcuit and says to follow diagnostic procedure 2 in the FSM. After performing DP2 everything checks out good. The strange part is once the key is turned off the problem, the code, and the warning light goes away.

The feel of the pedal is extremely hard when the problem occurs, and you can't hear the sound and feel the pedal pulsing under your foot, like you would when the ABS is functioning, in this case the pedal is just rock hard, it almost feels like the pressure is not getting to the calipers and is just blocked off. Normally when the ABS would activate it would pulse the brakes stopping them from locking up, but the pulsing doesn't seem to happen, and at the point of the the hard pedal there is absolutely no brakes.

Is this a know issue, has anyone else experienced it, and is there a fix?

[scotty-2-forty]

That's a lot of safety concerns ... This information might be better suited for the online mechanic section: nissan-online-mechanic.html

[RocketScienceRacing]

Thanks, I posted it there as well.

[IBustV8s]

well if the pedal is rock hard u might have lost your power brakes. possibly could be the brake booster

[RocketScienceRacing]

No its not a booster if it was the problem would always be there, this is electrical, it could the ABS pump not activating. I think the fact that the pedal gets hard is because the ABS sensor sense that the wheel is about to lock up it then reduces the pressure going to the caliper by restricting the fluid thats why the pedal gets hard as I'm pressing but the fluid has no where to go. At that point there is no more pressure going to the caliper so the car doesn't stop, until the the ABS ecu realizes something is wrong and converts the car to non ABS mode at which point the fluid restriction is released which allows the pedal to sink to the floor and the brakes then lock up.

The problem as I see is is after the pedal gets hard because of the restriction, the ABS pump (motor) is not activating, to reapply the pressure and pulse the brakes (which is what abs does as its faster than the human foot can). I'm pretty certain of this, as when the problem happens I don't feel any feedback on my foot as you would when the ABS is activating.

What makes this tricky is once the key is cycled the problem goes away, until it happens again, and it doesn't happen everytime the brake is applied. Also once the key is cycled the code goes away as well so the only way to read the code is when it happens and the ABS light is activated. But as I said before I got code 77, but after doing the Diagnostic procedure 2 we found no problems, I have even swapped the ABS ecu with another one and the problem is still there.

[scotty-2-forty]

Maybe the motor in the ABS Actuator froze up/went bad ... or maybe the solonoid valve relay or motor relay themselves? Did you check those?

[RocketScienceRacing]

No I haven't, is there any special test for the relays, or do I just test as you would a normal relay. And how do I test the motor in the actuator?

Wouldn't these problems show up as an ABS code?

[scotty-2-forty]

No I haven't, is there any special test for the relays, or do I just test as you would a normal relay. And how do I test the motor in the actuator?

Wouldn't these problems show up as an ABS code?

I've experienced problems that throw no codes, and codes without problems . In any event, while I'm not an ASE certified pro, I can only offer my experiences (thus why I recommended you have one of the Nissan pro's review this in the other forum). However, you might find this helpful for your own self-diagnosis, http://www.nicoclub.com/FSM/240sx/1996/br.pdf ... ABS starts on page 25, but 35 is the Trouble Diagnosis section. Brakes are EVERYTHING when it comes to your overall safety, so again please get answers from the pros too.

[RocketScienceRacing]

Keep the suggestions coming, I appreciate it. I have the S14 manual for the s14 200sx and at first glance its the same as the one you posted for the 240SX except everything being on the opposite side, but I will look at it more indepth later tonight. I did post this where you suggested.