Road speed signal

[Jean]

Hi,

I remember from m30 swap days that motronic 1.3 didn't really care about road speed signal wire , but it mattered more for 24v vanos swaps. I am wondering if it's something that also is important for proper m60/m62 (non vanos) running as well?

Thoughts , comments ?

I am cleaning up wiring before scheduling California bar inspection appointment for my swap; and would hate to fail it for something dumb like a missing signal that they can discover if it throws a code in dme ?

Thanks

[delamaize]

I'm pretty sure the 404 DMU reads speed from something, Because when I get to 115 in mine, it falls on it's face. Doesn't mater if you are in 5th or 6th....

[Jean]

Yeah, so wondering if DME stores a code for it?

[Jean]

Back of the cluster has a green connector known as "C6" ...is this where you guys connect VSS wire?

I just went through 84 ETM, from start to finish and couldn't find pin-puts for the C6 connector, it's got 4 pins where it slides into the instrument cluster....not all 4 of these end up on the same pins on the external side of the C6....

I've already confirmed that C104 is just got Tach and MPG, yellow/white (mpg) and black (rpm/tach).

Would really like to confirm what you guys are all doing for VSS, is it pin #6? (BU/YL) on the C6 connector labeled as "Vehicle Speed Input" on the cluster side?

But which pin is #6 ?

[Mykk540i/6]

In the 404 DME there are 2 tables with axis identifier 1C which is Vehicle Speed, both tables are 8x1 bytes long one contains what appears to ignition data and the other fuel data. It's tough to say when they actually come into effect and are used by the DME for vehicle operation.

There are also two sequential bytes of data near the beginning of the code, one for actual vehicle speed limiter. The other byte is Speed Limiter Hysteresis.

The DTC data in the 404 programming code uses INPA codes, that actually directly links the code number to the DME pin that the sensor connects to. Speed signal goes to pin 42 in DME harness, the error code for speed sensor is Error 42 and then gets translated to CEL flashcode 1234.

When the DME recognizes an error code it will either ignore the associated maps all together or make it reference a "limp" map to compensate. Since everything in the M3.3 is all about Load, and how what effects Load it could simply just take that one piece of the puzzle out of the Load equation during calcs.


So, yes...the 404 does indeed use vehicle speed input. I can see in a stock 404 .bin that the error 42 speed signal DTC will not turn on a check engine light. But it will be stored and referenced with either a scanner or stomp test.

[Jean]

Hi Mykk! Thanks for confirming it from the DME code perspective, appreciate it.

With a spare cluster, I confirmed yellow C3 pin 26 (BR/RD) has continuity with the "A" pins on the Green C6 connector...so I'll run a wire from there to the DME.

[robiniscool]

I'm running digital gauges so I don't have the clean signal that the oem speedometer gives to the dme/abs after receiving the signal from the differential. What I ended up doing was slicing the yellow wire from the camshaft sensor to the speed input of the dme. I believe that is the signal wire from the camshaft. It gives a pulsing signal so it would trick the dme that it is actually moving so you won't get any problems at certain rpms. Without the pulsing signal the dme would think your car isn't moving.

[Jean]

I'm running digital gauges so I don't have the clean signal that the oem speedometer gives to the dme/abs after receiving the signal from the differential. What I ended up doing was slicing the yellow wire from the camshaft sensor to the speed input of the dme. I believe that is the signal wire from the camshaft. It gives a pulsing signal so it would trick the dme that it is actually moving so you won't get any problems at certain rpms. Without the pulsing signal the dme would think your car isn't moving.

Ha! Did you do this at the DME side of the harness, would probably be shortest path? You did a a simpl "Y" connector off the cam sensor?

Have you scanned the DME/car to see if it's complaining about anything, or did that really trick the DME and it's not throwing a code?