2003 Rav4 SWB MkII ABS Issues

[bluestoesonnose]

Hi All, being driven to a mental break down and empty bank account with the ABS on our 2003 SWB Rav 4, the brake pedal "flutters" on light braking and the brakes go into ABS mode, even on perfectly level good surfaces!!

To date I've:

• Replaced all the wheel sensors
• Replaced the ignition switch
• Replaced the Yaw Sensor
• Sent the ABS module away for testing (it was fine)
• Replaced the brake fluid and re-bled the systems on more than one occasion
• Fitted a new reluctor ring to one wheel (rear near side) as the original was cracked!

In short everything that can be replaced has been

Whilst all this has slightly improved the symptoms it's never cured it, any ideas before I scrap the car?

Cheers

 

 

[gjnorthall]

The ABS unit is detecting a different output from one wheel sensor compared to the other three. From the checks already carried out, and, I'm assuming that the ABS warning doesn't illuminate - I'd conclude that the system is working as it should. An oscilloscope connected to the four wheel sensors would allow the culprit wheel unit to be detected. A low output from one sensor when braking would suggest a wheel locking up - this may actually be the case or something is causing a low output and the wheel isn't actually locking up. There are a myriad of possible issues - many that you have already ruled out.

- Different size tyres either side of an axle or a different construction of tyre either side - a space saver wheel will sometimes cause the ABS to kick in when braking.

- A worn wheel bearing resulting in a variable gap between the reluctor ring and sensor during braking

- A slightly displaced reluctor ring on one wheel.

Did the problem start after having work done on the car (replace wheel bearing, driveshaft etc)? 

As you've demonstrated - this type of problem is difficult to bottom out and I'd first suggest getting the output traces of the wheel sensors measured with an oscilloscope.

 

[bluestoesonnose]

Cheers, no idea where i'd get a scope from, so I'll start with the wheel bearings