2002 ABS Code 52 and alarm

[jeffcoseo]

I'm hoping someone has experience with the '01-'02 4Runner and can help me diagnose an ABS issue. Truck has been nearly flawless to 236,000 miles with the exception of Evap Issue and a Double Cardan rebuild (fun). A few days ago the ABS Light and Dash Alarm struck me about 4 miles from home - it went away 2 minutes later. Three days pass - the same thing happens again. Now, it happens every time I drive, intermittently.

I assumed it was an ABS wheel sensor - and I'm not afraid to drive a vehicle without ABS. My wife never drives the car, so I didn't panic. But now, I'm reading and learning about Hydroboost, Accumulators, Commutators, Booster Motors... and potentially brake failure... and I'm much more nervous that I'll lose brakes all together.

The ABS diagnostic port gave me a code "52" when E1 and Tc were jumped.

Thank you in advance for any insight!

 

[cfranck1]

Are you sure its "52"
Because I don't come up with a "52", but do come up with a "72"

I included a picture of all the abs codes for Tc and E1 jumped

 

[jeffcoseo]

Yes, it is definitely code 52.

The manual says "Hydraulic Booster Pump Malfunction" for code 52.

I don't understand if this is the pump for ABS assist - that pulses the system when ABS is activated... Or is this the pump that always provides braking power to the truck...?

I was very attentive on the way to work this morning. You can hear the little whirring motor, then pssht, pssht, pssht for the first 3 miles, then the ABS alarm goes on. The little whirring sound can't be heard over the alarm - so I don't know if it's present or not. Then, ABS alarm kicked OFF after 10 miles. I could hear the little whirring sound again - maybe for 5 seconds, then it clicks off. At that point, I do not hear the pssht, pssht, pssht sounds.

Then, the rest of my drive to work is normal. I hear the whirring sounds every 4 or 5 times that I hit my brakes.

Are these the craziest brake systems ever? I see people spending $2300 to replace the master cylinder - which is outside my budget on this truck. How do these pumps work? What do they do?

 

[cfranck1]

A great article on how the hydraulic pump brake system works.
Hydraulic Brake Booster

On ours, they incorporated the ABS HCU and ECU and the normal brake booster all on the same unit. Thats why the whole unit is so much money.

Diesel engine are the same way, they don't produce engine vacuum (unlike a gas engine) so they need a pump to produce vacuum.

Any abnormal noises? How is the brake feel? (hard, soft pedal)??

 

[jeffcoseo]

So, the pedal feels totally normal. The brakes work great, like they should, I guess. I never activate the ABS on any of my cars or motorcycles, so I don't know if it's working better/worse than before.

The "blowoff" sound definitely has my head spinning. When the pump works normally, it cycles for 5 seconds, then clicks off. When I'm having problems in the morning, I hear the little whirring pump for 3 minutes, and a little pusssssht, pussssht, every 2 seconds. That's when I have a problem. As if there is a little blowoff valve in there with too small of a spring on it.

And there must be some logic in that computer that allows the boost pump to cycle for 300 seconds or something before it gives the alarm. I'm always 3 miles down the road and that alarm comes on.

I see guys yanking their ABS fuse - does that disable the electronic booster pump on the '01-'02 trucks? Or does that little pump keep working off a different circuit?

 

[BlackWorksInc]

Interesting...

DTC C1252/52 -Hydraulic Brake Booster Pump Motor On Time Abnormally Long

Basically as you noticed it is over pressurizing the system to the point it seems to have to bypass pressure back into the system. It could be a couple things according to the attached section of the FSM regarding that particular DTC. Honestly I would probably go to check the pressure switch first myself, but I would try and follow the trouble shooting guide in the attached .pdf as best as possible.

The issue hopefully is in the circuit, something like a sticking/faulty relay or switch and/or corroded/damaged wiring than a whole brake booster unit. Not something I see too often to be honest with you, even on the newer 4Runners, Tacomas, FJ Cruisers, Prius, ect. that use this system.

View attachment CI__C1252_52_.pdf

 

[jeffcoseo]

Thank you for the reply, that is great information. So, if the booster is over pressuring the system, there is an electrical sensor/switch/relay that is not communicating to shut off the booster pump - is that right?

And there a bypass valve that lets pressure escape back when the system is over pressured?

I'll try to test these circuits tonight. It seems like either the blowoff valve is opening too soon, so it never builds appropriate pressure. Or the switch is stuck so it never senses appropriate pressure. And I bet you're going to tell me that neither of these little parts is replaceable... and I bet we're staring down the barrel of a $2000 gun... aren't we?

 

[cfranck1]

Here is a break down of the HCU
Don't know what is available separate? if anything is?

 

[jeffcoseo]

That "Pressure Sensor" looks kindof promising... I wonder if that bad-boy is sticking open and not sending the right signal. Looks cheap and easy compared to a WHOLE NEW STINKING UNIT!

I can't tell where that blowoff valve is on the diagram.

It has to be one or the other.

 

[zjf2000]

I am going through the exact same thing right now. Did you ever solve you issue? What was the culprit. Any help/insight is greatly appreciated.