2005 Cayenne Turbo Brake Light Switch Location

[scharf]

A few weeks ago, I installed an aftermarket tuning chip in my 2005 Cayenne Turbo. Car runs perfectly, with one exception (which may or may not be coincidental, since I didn't really notice it until about a week later):

I don't have to push the brake pedal anymore to start the engine (it starts now even without stepping on the brake), the cruise control doesn't work anymore (green light in the dash comes still on), and with the ignition on, I can shift into D or R without having to push the brake pedal. It seems as if the brake pedal switch is in a constant "pushed" state, but the brake lights work normally (they are NOT "always on").

Looked under the dash for the brake pedal switch per the TSB drawing, but didn't find it!?! The bracket across the brake pedal that should hold the switch is completely absent (pictures attached). I hear something clicking (like a micro switch) when I move the brake pedal, but can't seem to find a switch. Could it be on the other side of the firewall?

Is it possible for the switch to have gone bad as far as starting and cruise control are concerned, yet for the brake lights to work normally? And, if so, where is that **** switch in a 2005 Cayenne Turbo, and how would I replace it? Or am I looking in the wrong direction altogether?

Before anyone asks: I'm an electrical engineer and know what I'm doing with printed circuit boards and the like, so chances that I damaged something when installing the chip should be minimal (plus, I believe that if I had indeed effed up the ECU, a lot more wouldn't work anymore...).

Any thoughts? And if someone could point me towards the wiring diagrams for that car (especially with respect to brake light switch and cruise control), that would help, too...

Ron

[RFM]

I thought MY 05 brake switch is integrated in the ABS/pump unit, unfortunately i have no wiring diagram available to check it out.

[PTEC]

I believe the on 2005 and newer Cayennes the "brake switch" is actually a calculated from the brake booster pressure sensor... ie there is no brake light switch. 2004 Cayennes have the switch have the switch like your illustration.

Edited May 14, 2009 by PTEC

[Loren]

So your car is really a MY05 and the stop light control is provided by the ABS/PSM system.

Here is where the output signal goes on MY05 and newer.

[RishiHanda]

X

Edited April 6, 2013 by RishiHanda

[hahnmgh63]

TSB 9436 applies to 2004 and older Cayennes but it does give an indication on what a bad switch can affect on those models, as Loren posted, the '05 and later are different but the systems affected may be the same:

- the brake lights are continuously lit

- the cruise control does not function at times

- the PSM fails

- the vehicle cannot be started

[JeremyW]

I wish I would have read this post earlier.  I have a 2005 cayenne s and I am chasing down an abs/psm warning light with a P1276 code.  In the face of having to replace the ABS module (my wiring harness appears visually to be fine) I thought I would invest the $15 on a new brake light switch in the hopes that it may be the miracle cure that others have experienced.  The pig is fully apart and imagine my surprise when the brake light switch is non-existent under the dash and I discovered this post.  Just to confirm am I correct there is no pushrod switch in my car but rather it is electrical in nature despite the part supposedly fitting a 2003 - 2010 cayenne?  Thanks.

Edited December 29, 2016 by JeremyW

[lewisweller]

7 hours ago, JeremyW said:

I wish I would have read this post earlier.  I have a 2005 cayenne s and I am chasing down an abs/ psm warning light with a P1276 code.  In the face of having to replace the ABS module (my wiring harness appears visually to be fine) I thought I would invest the $15 on a new brake light switch in the hopes that it may be the miracle cure that others have experienced.  The pig is fully apart and imagine my surprise when the brake light switch is non-existent under the dash and I discovered this post.  Just to confirm am I correct there is no pushrod switch in my car but rather it is electrical in nature despite the part supposedly fitting a 2003 - 2010 cayenne?  Thanks.

Lol I made the same mistake. The switch is a hydraulic integral one on the abs pump or the master cyclinder.

For your fault code first check your battery is OK. 12.6v  engine off ignition off and 14v engine at idle or any rpm stable. 

Then check wiring for damage and moisture around connectors to the abs pump. 

Lastly the abs pump may have an electrical issue.

good luck. 

[rahul singh]

I am having some issues related to PSM control unit, as the car i am currently working with was repaired by somebody else, they guys replaced fuel pumps, ABS hydraulic unit, Brake booster..... Initally it was a no- start problem....... I tried my best, fixed some wiring connection from fuel pump side. Than i was able to start the engine...... but when i was trying to move the gearshift lever, it was struck in park, now i checked for brake light switch, i could not find it.... Connected PIWiS tester & come to know that PSM control unit has no signal going..... It was porsche cayenne 2006, the current faults in instrument cluster are " Brake proportioning fault ", and not sensing the brake pedal....

Any idea to share, From my side i will check furthermore & will update.  

[lewisweller]

12 hours ago, rahul singh said:

I am having some issues related to PSM control unit, as the car i am currently working with was repaired by somebody else, they guys replaced fuel pumps, ABS hydraulic unit, Brake booster..... Initally it was a no- start problem....... I tried my best, fixed some wiring connection from fuel pump side. Than i was able to start the engine...... but when i was trying to move the gearshift lever, it was struck in park, now i checked for brake light switch, i could not find it.... Connected PIWiS tester & come to know that PSM control unit has no signal going..... It was porsche cayenne 2006, the current faults in instrument cluster are " Brake proportioning fault ", and not sensing the brake pedal....

Any idea to share, From my side i will check furthermore & will update.  

Check for broken damaged or corroded wires in the loom harness under drivers (left hand drive) foot well carpet. Is the carpet wet? 

Battery in good shape?

 

[rahul singh]

Mr. lewisweller thanks for your kind reply.. I have found the problem, yes the drain was clogged, battery was in good shape. & when i did some contunity test, come to know that some of the wire (PSM control unit) were damaged..... Now I have fixed that problem.

 

[Loren]

[lewisweller]

16 hours ago, rahul singh said:

Mr. lewisweller thanks for your kind reply.. I have found the problem, yes the drain was clogged, battery was in good shape. & when i did some contunity test, come to know that some of the wire (PSM control unit) were damaged..... Now I have fixed that problem.

 

Good news. If you got any pics or more details pls post as it will help others in the future. Happy motoring. 

[StevieG]

Ok guys I have my psm fault and cause I have a Manual transmission my phc fault comes on instantly, my wiring lhs of seat is all dry I don’t even have any joins there at all, so where would I find the psm control unit ? Or that pressure valve if that could be the problem near the booster? 

Any help would be great please