mmccray

Does anybody know where the speeometer sensor is located on the transmission? Been searching the manuals, and parts list. I think Porsche actually calls it an impulse sensor.

Thought I'd ask before I go to work on it.

My 1990 964 just developed the infamous - speedometer works intermittantly problem - . I've checked the topside, and everything seems to be ok. I've searched the threads and found some discussion of the problem, but I'm not sure where the sensor is on the trans - top, side, LH, RH - or if there's anything in the way, etc...

Anybody know?

Thanks!
Marshall McCray
1990 964 C2
1987 944S

Sten

Can't say for definite on a C2, but early C4's have the pickup in the left side of the transmission, next to the ouput flange (left side of car as you're sat in the driver's seat), later cars derive the signal from the PDAS/ABS computer and convert it through what looks like a relay in the fusebox (I think it was R24 - it's coloured blue).

Barry

JasonAndreas

On a MY89-90 C2 and C4 it is located in the same spot.

Heirsh

Hey Marshall,

Ever eaten at the Szechuan Inn (I think that was the name) in Salem or Roanoke? Best Chinese I've ever had. Although their buffet isn't (or wasnt) very large.

mmccray

I jacked the car up and looked at both sides the transmission. The only sensor/switch that I could find was on the RH side about midway on the transmisison housing. I managed to break off on the connecting prongs. Fortunately, I had some electrical repair parts. Cleaned everything up and reinstalled. BUT now - I guess I'll look again on the LH side to see if I missed something.

I'm wondering if I might have disconnected and cleaned the reverse (backup light) switch instead of the speed sensor.

I've got to by a lift!! Jacking this thing up crawling under it - is getting tough on me!!

BTW - Heirsch - Yes I've eaten at the Schezuan Restuarant, but it's been awhile. Roanoke, VA has a lot of nice restaurants and is a great place to drive the Porsche!

Thanks!
Marshall McCray

JasonAndreas

Yup, that is the backup light switch. The TSB noting the change only gives the model years and doesn't list VIN numbers before/after the changeover.



Wheel Speed Sensor - Modifications


91porsche03

August 16, 1991

Model Group
911C2/C4/T 9
928 S4/GT

Part Identifier Number

9005 9106

Subject: Speedometer Road Speed Signal

ATTENTION: Service Manager/Service Technician

Models Affected: 911 Carrera 2 with manual transmission 911 Carrera 4 and 911 Turbo, Model Year 91 (M) 911 Carrera 2 with Tiptronic transmission from Model Year 90 (L) 928 S4 and 928 GT, Model Year 91 (M)

Concern: Speedometer road speed signal produced by ABS wheel speed sensor.


Figure 1




Vehicle Information: The road speed signal for the speedometer and several other control units is produced by the left front ABS wheel speed sensor. The reed contact in the transmission was eliminated.

In order to supply the speedometer and several other control units with the same signal frequency as before, a frequency conversion unit (FCU) installed in the central electric board converts 45 ABS road speed signals per wheel revolution into 8 signals per wheel revolution (Figure 1).

Frequency Conversion Unit Location on CEB

911 Carrera 2 and 911 Turbo - R 52
911 Carrera 4 - R 24
928 S4 and 928 GT - XIX


Parts Information: Frequency Conversion Unit Part Numbers:

911 Carrera 2/911 Turbo: 964 618 220 00
911 Carrera 4/928 S4/GT: 964 618 221 00