Prado 95 ABS not working

[jordan_sorabjee]

Good Afternoon All,

Need a bit of help. My 1kz te is fitted with ABS, but no matter how hard i brake it never engages. The ABS light comes on as usual with the ignition but turns off once started. If I disconnect any of the connectors (ABS pump or deceleration sensor) neither the ABS light nor the engine warning light come on to indicate an issue. Any idea? Could the ABS ECU have been removed (not that I know where to find it).

Thanks in advance.

 

[Beastrider]

Hello - which kind of surfaces are you driving on? Can you feel that the wheels have locked up during braking? Or maybe a friend could watch from outside?
I deliberately provoked my ABS into working when it last snowed but I was surprised that the pulsing felt through the pedal was relatively gentle compared to other cars I’ve driven. It also took a lot more provocation than a 2wd car.

 

[chadr]

Very hard to provoke my 95 to activate the ABS on tarmac.

However on snow or gravel it's relatively easy. If you have grass field, especially if wet, is also a good option.

 

[AdventureWagon]

Mine doesn't have ABS and I've not skidded on dry tarmac even south of the Brisbane river. I did have one or two wheels lockup once when hard braking in the light wet but nothing else even in heavy rain.

I second the wet grass suggestion though, especially on a light hill!

 

[jordan_sorabjee]

Im on about 50:50 tarmac and dirt roads. On regular emergency braking (live in Kenya and the driving is terrible) the wheels do lock up slightly but I have never felt the pedal pulse. Could it be possible that the ABS rotors in the hubs have gunked up? Thought it weird that the engine warning light didn't show an error when I disconnect the ABS pump.

 

[AdventureWagon]

Could be worth unplugging the MAF or similar to cause a check engine light and see if the ABS also comes on. Perhaps the system is disabled or removed and the ABS lamp is wired to the engine light?

I would think if the sensors are gunked up this would cause an ABS condition, especially if the actual Speedo works ok.

 

[jordan_sorabjee]

I know the engine light and ECU is working when it comes to the other sensors such as CPS, water and oil temp etc. I guess I could disconnect one of the actual ABS wheel speed sensors to see if that brings up an error. Anyone tried cleaning the ABS sensors?

 

[Beastrider]

Hi - if you disconnect/remove one of the sensors, you should definitely get an ABS warning light because the sensor won’t detect the ridges/troughs on the ABS ring. I think this is the easiest step to finding out if the system is connected. You’d get the ABS light on if one or more sensors was gunked up, for the same reason.

 

[jordan_sorabjee]

So I have disconnected the front right ABS wheel sensor, still no ABS light. Any idea where the ABS computer is located?

 

[AdventureWagon]

I assume you disconnected the sensor and then drove it (say at least 20km/h for 100m). It might not detect the signal absence without the car moving (and all the other sensors then working)

 

[jordan_sorabjee]

Yup. Drove a few KMs as still nothing

 

[Beastrider]

According to the Haynes manual, the “typical location” of the ABS ECU is above the brake pedal - see photo. Mine is a UK spec RHD Colorado 95, but my ABS ECU isn’t there. I am not sure otherwise.

 

[jordan_sorabjee]

Mines a Japanese import. Had a look and it isn't there either...

 

[Beastrider]

Ok - I just found mine. It’s on the side of the A-pillar, up and to the right of the accelerator pedal - see photo. The blue Aisin label on the ABS ECU can just about be seen.

 

[jordan_sorabjee]

Awesome, thanks. Just had a look and mines there too. Ill pull off the panels tonight to see if its all connected up

 

[jordan_sorabjee]

Awesome, thanks. Just had a look and mines there too. Ill pull off the panels tonight to see if its all connected up

 

[jordan_sorabjee]

So checked the ABS computer and it is all connected up. I tried disconnecting and still no warning light. Went further and also disconnected the ABS pump, still no warning light. Reconnected everything and the ABS still doesn't work. Any ideas on what to try next? Was thinking I could open up the ECU to see if anything has been burned out by why would it not bring up a warning light even if that were the case?

 

[Beastrider]

Hi - I don’t have an answer for you. It doesn’t make sense that the ABS light doesn’t come on when you disconnect things, but the light is clearly working when the car starts.

I looked on the wiring diagrams for what feeds into and out from the ABS ECU. Perhaps something sparks a thought.....

1. Brake pedal switch
2. Difflock switch (turns ABS off, but I don’t think your Prado has a rear difflock and should switch ABS light on anyway)
3. Low ratio detection switch (not sure why this feeds into the ECU because I believe ABS still functions in low)
4. Wheel sensors
5. Deceleration sensor
6. Fuses (ECU-IG, Gauge, ECU-B) and ABS Fusible link
7. ABS Actuator
8. Earth
9. ABS relay
10. Diagnostic port
I am out of my depth when it comes to reading fault codes, but I am aware they can be read - different ways depending on vehicle age. Hopefully someone else can advise you on that.

 

[jordan_sorabjee]

Thanks a mil for looking into that. Agree it doesn't make sense. I have actually pulled out the whole ABS ECU which I have sent to an electronics guy to have a look at. I'm hoping I can start by discounting this before i fiddle with anything else.

I have actually worked out how to read the ABS and SRS fault codes. No faults on my SRS, and the ABS light doesn't even flash, hence my assumption that it could be the ECU.

After I have discounted the ECU, I will go through items 6-10 on your list above.

Checking point 6 should be easy. I am told there is a way to jump the ABS actuator with the battery to test it. Any idea?

In terms of testing the earth, that would make a lot of sense, but I have no idea how to check this.

 

[Beastrider]

Hi - I don’t know about the actuator test. Once the ECU is removed, you can test the earth continuity of the connector lead to a known good earth using a multimeter. Earth will be WB (White Black). I imagine the earth connection inside the ECU will get checked by your electronics guy.