CRC-1000 Dakota Digital DBW Cruise and a GMPP LT4

[stan65]

All,

I'm trying to get my cruise to work and I have a strange anomaly.

The cruise only functions when I have my HP-Tuners MPVI2 plugged in. I do not have to have the laptop USB hooked up, just the MPVI2 dongle.

It took me a bit to figure out why it worked sometimes and not others.

If I start the car without the dongle and go for a drive, the cruise will not engage. The light on the CRC-1000 goes green when powered on and turns amber for a second and back to green when I attempt to engage. (Dakota tech support says something is not allowing it to engage, and I would have to agree with them) lol.

If I start the car with the dongle and go for a drive, the cruise will not engage. and function perfectly. The light on the CRC-1000 goes green when powered on and when engaged turns amber and stays amber until I hit the brake or clutch at which time it goes back to green. If I unplug the dongle while driving, it will immediately shut the cruise off.

Any suggestions or explanations?

I tried adding a 60ohm terminating resistor across pins 6 and 14 at the ALDL with no success.

Thanks,
Stan

[blitzer454]

How do you have the brake and clutch inputs to the CRC-1000 connected. My guess is that you need to add a pull-up resistor on one or the other or both.

[srode1]

Are you sure the CRC-1000 works with your LT4 E92 controller? I thought it only works with the E38 controller, but could be wrong. I ordered the CRC-2000 instead after talking with Dakota Digital about compatibility.

[blitzer454]

Both models will work but I think the problem will still be present with the CRC-2000. I think the root problem is that the input I/O cell on the controller chip is an open drain I/O cell that has not been connected properly. If you were to measure the voltage on an open drain I/O cell with nothing connected to it the voltage would be indeterminate. It could be at 0V or maybe the same as the battery voltage or anywhere in between.

So for example if you have a clutch switch such that when the clutch pedal is pressed the switch closes and completes a circuit to ground and you connected this switch to the CRC-1000 without a pull-up resistor the voltage at the I/O cell before the clutch pedal is pressed will be indeterminate and if that voltage happens to be below the ON threshold (active low input) then the controller would think the clutch pedal is being pressed even when it is not and the cruise would not engage.

A possible reason why the cruise only works when the MPVI2 is plugged in is because that circuit shares a common ground with the CRC-1000 which can change the indeterminate voltage just enough such that the normal voltage before the clutch pedal is pressed is just above the ON threshold and everything works. But most likely you would probably see some random failures even with the MPVI2 plugged in as changes in operating temp, humidity etc.. could change the voltage just enough to cause it to fail. So in this example the fix would be to add a pull-up resistor to the battery on the I/O cell such that there is no indeterminate voltage before the clutch pedal is pressed.

[stan65]

blitzer454,

Thanks for the last response. Been a while since I looked back at this thread.


I bought a second MPVI2 and added a parallel OBDII connector. Although this was not a cheap solution, it has worked flawlessly.

When you mention "add a pull-up resistor to the battery on the I/O cell" are you saying add the pullup resistor to the input point on the CRC-1000?

You have resistance in mind? I am willing to try to do this without the dongle.


Also in my first post, I miss typed and said not..... the "not" shouldn't be there

If I start the car with the dongle and go for a drive, the cruise will not engage. and function perfectly. The light on the CRC-1000 goes green when powered on and when engaged turns amber and stays amber until I hit the brake or clutch at which time it goes back to green. If I unplug the dongle while driving, it will immediately shut the cruise off.

[blitzer454]

Originally Posted by stan65

blitzer454,

When you mention "add a pull-up resistor to the battery on the I/O cell" are you saying add the pullup resistor to the input point on the CRC-1000?

You have resistance in mind?

Yes, add a pullup to battery voltage on the clutch or brake input to the CRC-1000. A 10k resistor will work. I would start with the clutch since it's more likely to be the problem.

[randy]

Where are you pulling your speed signal? I had to use the signal from the transmission harness connector on the gmpp ecu. Speed signal wasn’t accurate since we didn’t use the 40 tooth transmission. We flashed the ecu with a tire and reluctor conversion to trick the ecu speed and now everything is perfect

[stan65]

Final conclusions.....

After extensive testing, my conclusion is the GMPP ECU does not transmit the data on the bus unless its polled. Without the TCM in a manual transmission application there is nothing to poll the ECU. When the HPTuners dongle is attached to the ALDL connector, it is polling for data and therefore the Cruise control works.


The solution I opted for is to add a second ALDL connector to the bus and attach a used cheap HPTuners dongle to the extra port. (Yes I can have 2 Hptuners dongles attached to the car at the same time to continue to tune)

I didn't want to leave my "good" dongle in the car.

Thanks,
Stan