ABS Light/System Mysteries

[CJordan]

Started to get an intermittent ABS light on my 2001 base 986 Boxster 2.7L. No ABS codes upon scanning. Strangely, when the ABS light comes on the rear spoiler deploys and will not retract. Schwaben scanner indicates generic error 35 for "Interface with instrument cluster (see instr cluster FM). After sitting overnight and upon cold startup, ABS light is off; spoiler can be manually retracted with kick panel button. ABS tested good with a panic stop. After driving about 10 minutes, ABS light comes on, spoiler extends and now get DTC 9111 "PSM/ABS control unit". Research suggests that the connectors to the instrument cluster may be deteriorated and not maintaining contact. Would this affect an error code for the PSM/ABS Control Unit? Have not yet examined ABS wheel speed sensors or connectors. Suggestions for proceeding? Thank in advance.

[Loren]

Sometimes you can get an ABS error from wheel slip - either from wet pavement or loose gravel. In those cases it usually clears itself.

Also, if your battery is 4 years old or older it should likely be replaced - a weak battery can cause all kinds if anomalies in these cars.

[CJordan]

Thanks for the input. Battery is good, as is the alternator. Will investigate circuit integrity at instrument cluster, then wheel sensors/connectors. Also read that intermittent issues with brake light (pedal) switch can contribute to problems. Will also check that. Spoiler behavior still puzzling. Is it functionally tied to ABS somehow?

[Loren]

1 hour ago, CJordan said:

Will also check that. Spoiler behavior still puzzling. Is it functionally tied to ABS somehow?

 

Only to the extent that both signals go to the instrument cluster. Both are just warnings spoiler extended light or ABS activated light. 

I would treat as separate issues. 

[CJordan]

I'm not getting a spoiler light. When the ABS light comes on, the spoiler deploys into the "up" position and remains there. I cannot retract the spoiler until the ABS light goes out (usually after sitting overnight).

[CJordan]

Problem was eventually traced to a faulty ABS pump/control unit. It did not hurt to replace all four deteriorated ABS harness connectors in each wheel well along with wheel speed sensors with cracked plug connectors. One of Porsche's worst material selections for such duty.