PSM and ABS warning

rhys.williams007@yahoo.co.uk · Aug 9, 2016

Hi,
I seem to have an intermittent problem with the warning lights coming on for the PMS and ABS. It usually goes off when the car is restarted. Anyone have a solution or should I be concerned? Doesnt seem to have an effect on the car? Been happening on and off for a while. I do have a suspension issue to sort (front coffins I think). Would that cause this? Daft question probably.
Thanks for any response.

paulus · Aug 9, 2016

I had that a few years ago - would usually happen while braking on rough roads . Various people on here pointed me at a faulty brake light switch.
(the combination of ABS sensor seeing a sudden speed change & the faulty brake light causes the ABS ECU to interpret as possible ABS fault & illuminate those warning lights)
I had someone couple a tester up to the car & that was confirmed the likely culprit. £ 10 later & new switch fitted by me & problem banished !

Paul
2004 911 C2 40th Anniversary

matsleight · Aug 10, 2016

Same for me, simple check for an Indy to run and replace in a few mins

Richard_Hamilton · Aug 10, 2016

The 3 most likely culprits are:

Brake light switch - note that even if the brake lights are working properly, that doesn't mean it is OK. There are two sets of contacts inside.

MAF Sensor - this happens because the DME and ABS/PSM controller communicate, and there is an implausible signal sent from the DME to the ABS/PSM. This won't throw the Check Engine Light (as you would expect) because UK 996s are not programmed to switch on the CEL due to a failing MAF. This usually manifests itself on heavy acceleration.

An ABS Sensor - a failing sensor or bad connection can cause these symptoms.

A diagnostic check should reveal which of these is the suspect.