sb3

Decided to go for a drive today in my 99 C4 and about 30 minutes in I got both the ABS and PSM LEDs to light up. The break pedal did feel as if the brake booster/ABS pump was not working because the 996 brakes started to feel like my old 914. Still went for a spirited drive but when I got home I connected the car to my Durametric. The ABS/PSM 5.3 module seems to work fine, but the durametric tool could not return a code. Has anyone here had an ABS fault but no code return? Also, during my drive I did stop and start 3 times and the ABS/PSM leds would light up again after a few minutes. Any ideas? should I just go ahead and replace the ABS pump? Thanks for your help.

Stotty

My PSM/ABS lights came on when the MAF failed (though don't know if it threw up any fault codes as I don't have a reader).

Nickshu

Do a search there are many threads on this topic. It can be an easy fix like cleaning your MAF and throttle body....but unfortunately it can be also be a needle in a haystack search if the issue is deeper. I had the issue on my 2003 C2 with no codes. Ultimately I think it was related to uneven tire wear/tire size difference because the problem went away when I got new tires, but I never really confirmed that just never happened again after new tires.

sb3

Great. So the PSM/ABS warning could be anything. I guess I start doing some more reading into this but I'm going to test out the ABS pump first to see if it could in fact be the problem. Thanks for the reply's.

Stotty

I'd clean the MAF 1st... mine did exactly the same as yours. Lights came on during hard acceleration. Restarted the car and they went off. The came on again shortly afterwards.

Fixed by changing the MAF.

sb3

Yes. I'm going to look at the MAF too but my brakes feel like they have no power assist so the ABS could be in fact the issue. Thanks for the reply.

hardtailer

A failed ABS won't change pedal feel but a broken (=no vacuum holding) brake booster will give you the feeling you describe.

sb3

Actually, what it feels like now after driving the car around a bit more is the pedal is not returning as quickly as it should after being pressed. I'm not sure what would be causing a slow pedal return. Anybody have any ideas?

Porschetech3

I had a case once where the brake light switch was faulty/ out of adjustment causing the abs to fault light to come on. Seems the abs expects to see the brake light signal before it sees brake hydraulic pressure, if it see's hydraulic pressure before it see's brake light signal it will illuminate the abs fault light..

sb3

I think the problem I have is simular to this. The brake pedal is not returning right away, almost like the return spring is weak or the pedal bushings are worn. The brake pedal seems to have some drag on the return. I'm going to take apart the pedal assembly this weekend and see what I can find.

sb3

I pulled the brake pedal switch. It keeps sticking in the off position. Looks like this was the problem. Thanks for the help.

Porschetech3

Glad you found it and it was an inexpensive fix !!!

montauk

This happened to me today. I replaced my water pump started the car to check for looks and let it warm up. I looked inside and saw ABS and PSM failed. I drove it anyway to let it warm up fully so I could check and see if I needed to add more coolant. When I got back, I hooked up code reader but didn't get any codes. I started the car and the ABS and PSM lights were out. I didn't drive it again but will tomorrow. Fingers crossed!!!!!

wyovino

Check that you plugged in the MAF cable securely after you put the air intake back in. I forgot that step once and got the ABS and PSM lights, but I think I got a code.