Haynes' World is a regular feature that takes a look at what the staff at Haynes are doing with their cars, bikes and other vehicles. This time, Martynn has triggered a 'VSC' warning on his Lexus after working on the rear brakes.
Car: Lexus RX400h hybrid
Owner: Martynn Randall
Our 2007 Lexus RX400h has been exceptionally reliable. I think the only thing that has actually failed in the seven years of ownership, and 140,000 miles, is the radiator springing a leak. Inconvenient yes, but not really the car's fault if it gets hit by a stone.
The annual MoT examination has also been a breeze, with nothing worse than an occasional advisory about tyre wear – until this year.
‘Nearside Rear Service brake binding but not excessively (1.2.1 (f))’ was the advisory this year.
After jacking up the rear of the vehicle (supporting it securely with axle stands), and removing the nearside rear wheel, I could clearly see some discolouration of the disc. The brake had indeed been binding.
I unscrewed the guide pin bolts, and easily pulled the caliper from place, which suggested that the piston in the caliper wasn’t the problem. However, just to be sure, I used a retraction tool to fully push the piston back into the caliper body. It moved easily and smoothly, so no problem there.
Looking at the pads, I could see that the outer pad friction material was significantly thinner than the inner pad, which suggested that it wasn’t moving freely.
Sure enough, the outer pad was well seized in the caliper mounting bracket, and took a few minutes of gentle persuasion before it would release.
I removed both pads and shims, then cleaned away any dirt and debris with a wire brush and aerosol brake cleaning fluid. With everything clean, I fitted the shims to the caliper bracket, and slid new pads into place. With the caliper refitted, I lightly greased the guide pins bolts and tightened them to the specified torque.
I gave the brake on the other side of the vehicle the same treatment, pumped the brake pedal a few times to move the pads against the discs, then checked that the pads weren’t binding any more – all good!
I refitted the wheels, lowered the vehicle to the ground and tightened the bolts.
Job done – or so I thought. Upon turning on the ignition, I was surprised to be confronted by a ‘beep’ and a warning message in the instrument panel: ‘Check VSC system!’, accompanied by the ABS and TC warning lights flashing.
The brake pedal felt ok, so I drove the vehicle for a few miles, hoping the warning would disappear – it didn’t.
What does VSC mean?
‘VSC’ stands for Vehicle Stability Control, and the message can be triggered after pushing the pistons fully back into the caliper bodies. There were various explanations why this would be so, but the consensus of opinion was that the ‘system’ detected an abnormal flow of brake fluid, assumed there was a leak in the circuit, generated the warning message, and shut down the ABS/TC system.
I suppose I can kind of see the logic to this, although I’m sure that I’ve done exactly the same procedure on the front brakes, with no resultant messages or problems. Weird.
Typical… my OBD scanner only has access to the engine management system, so it can’t search for or clear any fault codes relating to the chassis systems.
Luckily, I have a friend in the trade, who has the necessary kit to interrogate the chassis systems, clear any fault codes, reset the ABS/TC systems, and make the warning message go away. Otherwise, it would have been a trip to a Lexus or Toyota dealer.
Plugging the scanner in revealed one stored fault code: ‘LH rear brake hydraulic circuit failure’. With the code cleared, the warning message disappeared and the ABS/TC function was restored.
Fingers crossed it stays that way.