Cruise control not working

Hello,

I have a Passat car, manufactured in November 1993, with a 1Z engine.

I've now installed an aftermarket cruise control system. The installation wasn't a problem. Simply replace the faulty switch and connect the plug to the fuse box.

Then, head to the VW workshop and have it activated in the control unit.

It's not working now.

Does anyone have a tip? Where does it get the speed signal from, for example? How can I check if the switch is working properly? Or are there models where you have to do even more to make them work?

Best regards,

Hi,

If your relatively old model even has the GRA (Gas Recirculation) function in the engine control unit, you can, of course, check its functionality using the relevant measurement blocks.
Also, all the switches must be working (not just the lever, but also the clutch and the brake).
VAG-COM rules.

Best regards, Rainer.

GRA engine control unit? Well, I'm afraid I don't know anything about that.

Anyway, it should work starting from September 1993, so from that facelift model onwards.


The switches themselves would also need to be tested differently. I'll have to look for one of those sometime.

Since I've owned the car, it has been displaying the error message 'speed signal implausible - sporadic.'

Since I still have a tachometer wave, I think the tachometer is sending the signal. Since the indicator briefly gets stuck when starting and then immediately jumps to 30 km/h, I suspect that the cruise control will be deactivated right away.
Could it be?

Does it receive the signal from the ABS sensors?

Unfortunately, I still don't have a VAG-Com. I'll get one as soon as I have the money. Now, the cracked windshield has once again thrown a wrench in my plans.

Best regards,

Hi,

GRA stands for "Geschwindigkeits Regelanlage," which translates to "speed control system." Try searching in this forum; it's possible that very early TDIs didn't have this function in the engine control unit software.
If the speedometer signal is faulty, the GRA (Gear Ratio Adaption) cannot function. Okay, let's take a look at what's causing this faulty signal.

Best regards, Rainer.

Hello,

So, the GRA (presumably a device or system) can be retrofitted. Of course, I did my research beforehand.
The STG therefore supports the function.

The search for the implausible signal yielded the following:

The signal is not coming from the ABS sensors, because regulations require that the ABS sensors be specifically designed for the ABS system.

When the signal fluctuates by more than +-2 km/h, the cruise control is automatically deactivated.

The signal is likely to be found at these locations.
Cable color: blue/white.
Location: Radio ISO connector A; PIN 1.
Alternative: on or behind the fuse box, 1-pole. Plug.

But where does the signal come from?

As I mentioned, I still have a tachometer wave.

I would now claim that the speedometer is sending a signal to the control unit (ECU). Is that correct?
Does the control unit still have an additional sensor?

Or where can I find the component that generates the signal, and can I replace it?

Best regards,

If your model doesn't have a tachometer shaft.

Then the control signal is probably also coming from the transmission.
Otherwise, the speedometer wouldn't work.

Get yourself a wiring diagram.

I wrote that I have a tachograph.

Oops, I missed that.

Then it's likely that your engine control unit (ECU) isn't receiving any signal.
So, then it's probably nothing to do with GRA.

That's quite an old tank if it still has a speedometer cable.

Hello,

Of course, that's GRA.... VW offers the set, and the car is included in the list.

As previously mentioned, the control unit is receiving a faulty signal.

So, it receives a signal. In the case of false signals, the GRA (presumably a system or device) is deactivated, as I mentioned in my previous post.

I would like to know where the STG (Steuergerät - control unit) gets its signal. It probably comes from the combination instrument.
'Actually, I just want to know if there's a part available for swapping, because I don't want to have to take the instrument cluster in and out three times to figure that out.'


Best regards,

Hello,
I'm not 100% sure, but the signal probably originates from the control panel module.

I think I even read about it in this forum, in connection with the '1z Ruckel' issue.

Found it!

hallo! bin seit neuestem auch passat tdi 1z besitzer. das gute stück ist ez 02/94 , 216000km und hat den elektronischen tacho.

ich stelle bei mir das typische mengenstellwerk-ruckeln fest, d.h. bei teillast von 1500 - 2200 1/min ruckelts, besonders im 4ten und 5ten.

hab dann auch gleich den geschwindigkeitsgeber vom getriebe abgezogen --> ruckeln war weg! mein bekannter hat auch den passat 1z, allerdings mit ner tachowelle. er hat einfach den stecker vom kombiinstrument abgezogen und gut is (dh. die geschwindigkeit wird ganz normal angezeigt). verzichtet eben auf die komfort-funktionen, wobei ich beim fahren KEINEN unterschied feststellen konnte.

das ganze will ich jetzt auch machen, jedoch gibts bei mir den stecker am kombiinstrument nicht deshalb suche ich nach einer möglichkeit dem STG sein geschwindigkeitssignal wegzunehmen, oder läuft das signal erst zum STG und dann ins kombiinstrument??

Please provide the text you would like me to translate from German to English. I need the text to be able to provide a translation.

/viewtopic.php?t=5367&highlight=tacho*+jerking+1

Hello,

Thank you for the link. That's exactly the error that I'm also seeing.

00625 027
Speed signal.
implausible signal
Sporadically.

It's a shame that this thread is more about the pump than about the signal.

Best regards,

Hello,


Okay, I'm not sure if anyone is still interested, but I'm just going to share some of my further findings.

So, the clutch switch works in the same way as the brake switch.

The speed signal comes from a Hall sensor located at the back of the speedometer.

Okay, I'm going to replace the Hall sensor first. That seems like the most logical thing to do. Otherwise, it will probably be a new speedometer.

Cleaning it didn't make any difference.

Best regards,

Hi,

If you have a mechanical speedometer, it's very unlikely that the problem lies there, unless the shaft is broken and the speedometer needle is jumping erratically.
A Hall sensor is a magnetic field sensor, and in the speedometer, there is a rotating magnet whose field the Hall sensor reacts to. If the Hall sensor is not properly seated in the speedometer, it can occasionally miss a signal, which can then lead to the system shutting down.
The signal from the Hall sensor might also be used for a speed-dependent volume control (GALA) in the car radio. Check this and possibly disconnect it to see if the problem originates from there.

Regards,
dieter

Hello,

I have a mechanical speedometer.
The speedometer needle isn't jumping (otherwise I would have already replaced the sensor).

So far, the needle has only jumped directly from 20 km/h to 30 km/h.

After I removed the speedometer last weekend and cleaned everything, it's all working perfectly now. Except for the cruise control, of course. The jump from 20 to 30 is now gone.
Everything is verschandeln and securely fastened.

I can only think of the sender or a broken cable.

Best regards,

After a long wait for the hall sensor, the cruise control system is now functioning perfectly.

I thought I would never get it.

It's never happened to me before that I had to wait for over two months for a spare part from VW.
That really gives me something to think about.

What if that happens to a part while the car is still running?

Best regards,