John52

I removed the battery from my C2 (I needed it for something else). Removing the battery is something I do every year when I store the car, so it seemed like no big deal. However, when I re-installed the battery all hell broke loose. The ABS warning light stayed on and the warning beeper sounded. I went for a short drive and noticed that now the speedometer does not work and the indicator light for the tail stayed on. I don't know what else is not working as I quickly returned home when I noticed all these things not working.

Any thoughts , assistance would be appreciated.

John52

Problem solved!!!!
After posting my original question, I went back to my garage and carefully started retracing my steps as I couldn't believe a simple battery disconnect could cause this chaos. What I found was that when removing/replacing the spare tire or tool kit, I must have dislodged that massive connector that goes to the "black box" that sits next to the spare. I simply pushed the connector back in so it seated properly with a "locking click" and everything returned to normal.

What is that box anyway?

Adrian

Dear John,
That "black box" on a C2 is the ABS control unit and on a C4 the PDAS/ABS control unit. From your fault description it must mean you have a 1991 model or up C2. In 1991 the speed or pulse sensor was removed from the 964 gearbox and the speed input transfered to the ABS speed sensor circuit. This is why with ABS control unit disconnected the speedo did not work,
Ciao,
Adrian
911C4

John Boggiano

How interesting!

I'm off to check mine!

Adrian

Dear John B,
Do not confuse yourself. You have a 1990 model. Your ABS light only will come on but you will still have a speedo. You have the pulse sensor installed in the gearbox. This speed input from the sensor to the speedo also controls the spoiler warn system. However the spoiler is opened and closed via the ABS control unit. Basically Porsche simplified the system for Model Year 1991
Ciao,
Adrian
911C4

Taj

Hi Adrian,
Is there a comprehensive list of changes between different model years? WOuld love to know how these babies evolved.

Taj.

John Boggiano

Thanks, Adrian.

Yes, I realised that, but I wanted to check the plug/socket connection integrity.

Adrian

Dear Taj,
Yes there is but I am afraid you are going to have to wait to read them. They are in my book. There are some lesser lists around in other book. Peter Morgans 911 book for one. There are others as well.
Ciao,
Adrian
911C4

Jimmy Singh

Hi All,
I have a similar problem .

my car without the ABS module in the fuse box , speedometer works perfectly but and light on dashboard appears .

- when I put the abs module in the fuse box , my speedometer goes erratic .

my spoiler can only be manually controlled too .

any help please

VTLY

my problem sounds exactly the same as yours, could you please tell me which "black Box" are you referring to ? GREATLY appreciated.

ThomasC2

it’s The ABS control unit situated on the lower right hand side in the “frunk”. And it’s not black, it has a silver/steel plate cover. The connector is like 10 cm wide so you can’t miss it. You have to lift the carpet in the frunk to see it.