PSM OFF/ABS warning lights

I have replaced the brake switch and both the PSM and ABS warning lights still come on occasionally.
It always happens when I'm cruising on the freeway with my foot on the gas.
I'm not even touching the brakes.
Last time it happened when I got home I hooked up the OBD and there were no codes.
Any ideas what the problem is and what I can do to fix it?
TIA.

Quote
boxsterd
I have replaced the brake switch and both the PSM and ABS warning lights still come on occasionally.
It always happens when I'm cruising on the freeway with my foot on the gas.
I'm not even touching the brakes.
Last time it happened when I got home I hooked up the OBD and there were no codes.
Any ideas what the problem is and what I can do to fix it?
TIA.

In some cases a failing MAF can trigger warning lights from these systems. The MAF output is used to calculate engine load and if the MAF output is too far off this can trigger these warnings.

If emissions not affected there won't be a CEL nor any error codes. However, there might be pending codes, so be sure you check for those.

If it is the MAF the bad behavior from the MAF will initially be very intermittent. Steady "high speed" cruising puts a load on the MAF that could bring this behavior about. But if you pull off the highway the lighter engine loads means the MAF works less hard -- so to speak -- and can recover.

You might catch the MAF acting up if you have the ability to view/data log some telemetry while driving and then drive on the highway and try to reproduce the behavior.

Low battery voltage level can trigger these warning lights too. In this case the alternator is not generating enough electrical power to meet the car's electricity needs and the battery is then having to take up the slack. I have encountered this just once and the symptoms were observed in the service bay with the engine at idle. The dash lights would come on, the engine would then begin to run poorly, the die. The tech would shut off the ignition and wait. After some time the engine would fire right up and run ok until the behavior would return.

It is unlikely this is happening in your car's case, but you need to consider the battery's health and if it is poor why. The alternator plays a vital role in helping keep the battery healthy.

... revisit the brake light switch install.
A new switch is difficult to get to sit properly in place and may need a little tweaking with a knife or file to have it go through the keyhole and sit.
I have seen this exact issue before, just after replacing the brake switch.
Once it was re-seated properly, there were no more warning lights.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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