I have a 1991 348 that has been sitting for about a year and yesterday I finally got the time to take it out. My first step was to replace the dead battery, which went well. Then I started the car and it started right up on the first try. I let it idle for about 20 minutes and then took it for a slow drive around the neighborhood. That's when I noticed the brakes barely work and that both the red brake light and yellow abs light are lit. The manual says either there is not enough fluid in the reservoir or that the brake booster pressure is too low. I think it is the latter because the fluid level is at the max level. Where should I start troubleshooting? Is it worthwhile to remove the luggage compartment cover and check the fuses on the abs computer. Is it the abs pump that provides the pressure or is the booster somewhere else. The pressure accumulator is right next to the abs pump, so I was thinking that is the booster. Are there any other fuses or relays I should check. When I start the car, I do not hear, or feel, any activity at the abs pump. Isn't it supposed to make some noise at turnon. The fluid in the reservoir looks just like the fluid in the bottle, that is, it looks like new. But could brake fluid get nasty in the lines and cause a problem. Of course, I understand the the clutch uses the same fluid and the car shifts great. I only drove 2 miles very slowly, but the car even shifted into 3rd, and 2nd, so I know the clutch is working well. Is there any place else I should check? Thanks for whatever assistance you can offer, Chris
It sounds like it could be the booster mate. Does the car have a really HARD pedal? Could it be a sticking brake master cylinder maybe?? Also, I would still flush that old brake fluid out man. Suck the old stuff out and re-fill with new brake fluid. Then, flush the brake fluid out by cracking the bleed nipples on the brake calipers. If you can do the "2 man" bleed method, having someone pump the brake pedal while you are watching to see if fluid comes out will tell you if the brake master cylinder is working ok. Bleed brakes 1st man, then go from there.
Yes, the pedal is really hard. It is impossible to slam on the brakes and get the car to skid. There is nothing until the very end and then at the end, the grab is very light. It just rolls to a stop. I can try to bleed the brakes this weekend, but my gut feel is that there is no pressure in the system, so not much fluid is going to come out. I hope I'm wrong about that.
Yeah, donesnt sound good man! You should still be able to bleed them. Give that a go anyways, get that old brake fluid out.
Personally, I would certainly check the fuses under the luggage compartment carpet. The wiring diagram shows three fuses, which protect three relays. Fuse 185 (30amp) protects relay 186 (control relay for brake fluid pump). It certainly sounds from your description like the booster pump is not coming on to pressurize the system. That COULD mean that the pressure switch isn't functioning correctly (stuck in position from lack of use??), or that the pressure pump has failed, or perhaps even that a voltage surge went through the system when you replaced the battery, and that fuse 185 blew out to protect the system (this could particularly be true if you had the ignition switch turned on when you reattached the battery terminals.) Or MAYBE someone pulled out fuse 185 from its holder and swapped it into the holder for the A/C system, if that fuse was defective (which of course is very common). Anyway, check those fuses. If one is blown, DO NOT replace it with a higher amperage fuse! And I would suggest that you fill in your profile so that we know where you are located, and if your 348 is LHD or RHD. Please keep us updated on what you find.
When I let my Mooney sit for too long without flying it, its brake fluid in the outer portions of the lines went to a rock-solid state, though not so much in the reservoir itself...and you didn't get much braking out of it in that shape. Had to put in new brake lines...cheaper than the effort it was taking to remove the hardened brake fluid.
The 3 Amp fuse on the ABS fuse panel keeps popping (Fuse 183). When the ignition is turned on (with or without starting the engine) the ABS booster pump starts to work, then within seconds, it stops because the 3 A fuse pops. I have the schematic from workshop manual and this fuse is in front of the control relay for the ABS and provides 12V to the ECU connector and is also attached to the zener diodes for the brake pump relay. Unfortunately, I no electrical engineer, so I'm not sure what happens with the diodes in that relay, which connect with the brake fluid pressure switches. It seems that the ABS pump is working. If it works long enough, it may build pressure within the system. I kind of was expecting pump to be frozen and the 30 A fuse to blow, so this 3A fuse has me at a loss. Can anyone toss out why the 3 Amper is blowing? Thanks, Chris
Looking at the diagram, fuse 183 (3 amp) gets power off the 30 terminal on the ignition switch, and sends power to the 30 terminal on relay 182, which is identified as "control relay for ABS system during cranking". I don't think that relay 182 could possibly supply power to the fluid pump itself, if it only has a 3 amp fuse protecting its power supply. Relay 182 must simply send a signal to the ECU for the braking system, which then sends a signal to relay 186, which actually activates the pump. The power supply for relay 186 comes from fuse 185, which in turns appears to have a direct 12 volt power source. Looking at my own 348, I see something funny. There is a scotch-lok connector on one of the wires just below fuse 183. You might have a look there to see if your car has a similar connector, and if it might possibly have a bare spot that could be touching ground. That would blow the fuse. Next, try putting a new 3amp fuse into #183, then unplugging the wires from relay 182, then cranking over the engine to see if the fuse still blows. That would give you an indication of a short between the fuse and the relay. These are just basic checks. You could take it further, but the system is obviously VERY complex, and you shouldn't do anything that could cause a glitch in the circuitry. I believe there is a manual specifically dedicated to the braking system on the 348, although I haven't seen such a thing. The workshop manual tells you nothing beyond the schematic diagram for the wiring.
Miltonian, Thanks for your reply. I agree with your assessment of the brake relay logic. I pulled the relays one at a time from their holders today to see how the system would respond. When I took out the ABS relay (182), the fuse did not blow when I turned the key. So I know there is no short in that wiring. But there was no 12 V to turn on the other relays, so not much learned. Next I took out the ECU relay (188) and the fuse blew when I turned the key. So I can eliminate a short to ground in pins 85 and 86 of that relay. The good news is that I did hear the ABS pump for a second. Finally, I took the Pump relay (186), turned the key, and the fuse blew. While the relay was out of the holder, I checked the pins with my ohm-meter. Holder Pins 85 and 87 are shorted together, reading .2 ohms. Can this be right? I see that each connection has a wire that goes to the ABS ECU connector and goes to pins 14 and 32. The manual says Pin 32 is 12V from the pump relay, and I agree as this connection is running the ABS pump which I know works. But the manual says pin 14 is the pressure switch and it says it is ground. Would you know if pins 14 and 32 are supposed to be shorted together in the connector or on the ABS board? Right now what I measure doesn't match my understanding from the connector pin assignments. With pins 85 and 87 together, I have 12 V at pin 85, not ground like the manual says. Have you ever taken off the ABS ECU connector? Is is easy? Safe? (I package aerospace electronics for a living, so I'm not too afraid of poking around a circuit board, but I don't want to spend a few grand fixing something I shouldn't have been touching). Thanks for your help!! Chris
I'm no electrical engineer but i could figure it all out with enough time. I'm really lazy so here is what I think. You have a problem that goes beyond the abs pump. These cars will run fine and stop great if you deactivate the abs system except you can now lock the wheels in a skid. So the fact that your car is not stopping is an issue unrelated to the abs pump. Old fluid absorbs moisture which makes rust = frozen parts in your system. I would screwdriver the caliper to make sure the pistons retracted in the bores say 1/2". Then i would suck out the old fluid and pour in new. Then I would 2 man bleed the brakes and the clutch later on same reservoir. You really should be getting decent braking after this. As to the ABS system I would start by freshening every ground. Time corrode ground contacts all the time= increase resistence = heat= nonfunctional circuits. If then the ABS pump comes on w/o blowing I would 2 man bleed as I have posted before with key-on engine off to pressurize and bleed the system for a rock hard pedal. If the ABS is still not working I would do the electrical diagnosis you have started because that takes the most time. All the other stuff can be done in less than an hour and you have already spent more than an hour thinking about it.
Fatbillybob, your response made me laugh. I sure have spent more than an hour! But as I drove home from work thinking about this, I had to go mess with the car tonight. What I have found is that my 12V power line from the pump relay is shorted to ground. That is why the logic on the relays is all messed up and the fuse blows. Why it is shorted to ground is not obvious and will certainly burn a few more hours. Concerning the abs pump, I am under the impression that it is important to regular braking as it is the hydraulic brake pressure booster and it serves the same function as a vacuum brake booster in adding braking force in the master cylinder. Do you think my understanding is correct? I know that until I get the pressure up in the system, the red and yellow brakes lights will be on. While I have not tried, I'm thinking that without any pressure in my brake system, I can't get much fluid out when bleeding the brakes. Once I get the abs pump to run and pressurize the system, then I will be able to perform the brake fluid maintenance. Thanks for your guidance.
Nope. Listen to FBB! Your Ferrari will 100% stop with full power brakes even if the ABS system suffers catastrophic mid-drive failure. Now, for a real Stooge brake bleed, connect your Motive Power Bleeder (come on, it's a $50 or less part for a $50k+ car...a no brainer), turn your ignition not to Start, but to Run, open a bleeder on a caliper (actually, this works well for the clutch too), and then press your brake pedal enough times that your ABS pump kicks on. Oh wait...
I thought I'd post an update and ask another question too. My brakes work now, but to do so, I had to disconnect the connector to the ABS ECU. I have a short in Pin 2 (12V in) of the ABS ECU that blows the 3A fuse. With the connector off, the car braking system functions very well except that the ABS won't operate. Ultimately, I want to fix the ABS problem. Would anyone have a ABS ECU schematic to assist in the troubleshooting or any additional ABS info beyond the work shop manual. I would like to try to repair the circuit board in the ECU before spending $2000 on a new ECU. Thanks.....Chris
Bumping this up... Today I started up my car (which I drive at least once/week) and both my ABS and brake warning lights went on. The car still seemed to drive fine, but after around 10 times of hitting the brakes, they got really hard and I had a difficult time braking. This wasn't a fun realization on the highway. -I checked all the fuses and they're all ok -If I let the car cool off and then go for a spin the lights stay on, everything is ok for a few stop signs, but then the pedal gets stiff again -When the engine is off and the key is on, it take about 4-5 brake pedal pumps before the noise of the accumulator getting filled starts Any insight on what the problem can be? I wanna drive, I need my brakes!
This is incorrect. The ABS pump charges the nitrogen sphere with brake fluid. This is what is used to provide power brake assist. if the ABS pump is inoperative, you will not have power assist with your brakes, and it will be next to impossible to get the car to stop. The ABS system doesn't have to work, and you can disconnect the ABS ECU, but the pump and nitrogen sphere must work in order to have power brake function.
I just checked my codes and get 3.3 Sensor right rear LACK OF SIGNAL due to short circuit or breakage (or internal control unit failure) Can this code really cause my to lose my brakes?! I'm suspecting more a faulty main relay, which I have on order. Any insight is appreciated.
No that is just telling you at some point in the ECU's life it lost the signal from the RR. wheel speed sensor. It may not be a current fault, and it has no effect on normal braking, just ABS function. If the RR. wheel speed sensor is still not sending the ECU a signal, then the ABS will not work, but you will have regular power brake function.
I am bumping up this old thread. Yesterday my abs light stayed on constantly. I have the same symptom as ctanner. The 3 amp fuse protecting relay 182 keeps blowing. I hear the abs pump for a second or 2 then the fuse pops. I haven’t had time to dig into but I am hopeful there was a solution to that fuse blowing. I am looking for an easy way out. Probably just wishful thinking but worth a shot.
Aaron, relay 182 feeds the ECU and the solenoid of relay 186 (black?). If you pull relay 186, does the fuse still blow? If you disconnect the ECU, does the fuse still blow? Hope you have plenty of fuses for these tests
funny you should say that, I need to go pick up more fuses tomorrow. Thanks for the reply! I'll do some more testing tomorrow and try your suggestions and let you know the results. I appreciate the help.
Just be aware that relay 186 has power coming from directly from the battery (via one of the 30amp fuses). Try to avoid arcing when pulling and reinserting that relay. Does your car have a battery have a cutoff switch? I guess you could also try pulling relay 182 to see what happens. If your 3A fuse blows with that out, you might have a problem with the wiring from the fuse to the relay.
I do have a cutoff switch, I shut it off when I pull the relays out. I did get as far as testing with relay 182 pulled and it did not blow the fuse, so that's one thing down. I've found some of the schematics floating around, and I'm attempting to make sense of them. So far I think my relays check out with just simple resistances tests. I don't have continuity between pin 30 on relay 186 but from what I can deduce from the diagrams, that is the way it should be.
You can leave checking of the relays themselves for later. As advised by Ian, after the relay 182 pull out check, do the relay 186 pull out check. If the fuse still blows, disconnect the ABS ECU and see what happens with the fuse. This will tell you where the problem is.
