Attessa engages fully on reverse or slow speed

[dodo1410]

I have a 1991 r32 gtr, and ever since I dropped the engine for a rebuild I’ve been having an issue where the attessa would fully engage on reverse and on first gear on slow speeds. It’s been happening for a year and now I hear a locked diff clunk when it engages again.

The car is on a motec m800 ecu with the stock ecu also plugged in. I already bled the attessa system and changed the front n rear diff oil. I also unplugged the hicas fuse from the trunk to check if that was the issue, and I’ve checked all the fuses and all are fine. I’ll link the video of the attessa engaging. If anyone has any suggestions on what to do next let me know please.

[Duncan]

hmmm, well l can see from dash gauge that it is trying to engage ATTESSA at a weird time. Can you confirm the 4wd light turns on with the ignition key and then turns off again (not on or blinking) after you start the engine, ie ATTESSA ECU does not think it has an error?

Do you know anything specific about how the Motec and stock ECU are wired in? Per page CH-66 of the manual, ECU pins are meant to be wired to ATTESSA and some aftermarket ECUs do not fully allow for that (although I guess Motec is a full custom wire in anyway).

ECU 37 (RPM) to ATTESSA 31

ECU 56 (TPS) to ATTESSA 47

ECU 30 (TPS earth reference) to ATTESSA 48

 

[dodo1410]

Hey Duncan, yeah the 4wd light works fine on ignition and turns off normally with all the other lights, and as for the motec wiring it’s spliced in. I’m going back to the shop to check the ecu pins as you’ve mentioned as that could be the culprit.

 

thanks, I’ll keep you updated.

[Duncan]

The other thing that comes to mind is a failed g sensor, but it might be tricky to swap it for a different unit if there are not a lot of other GTRs around

[dodo1410]

10 minutes ago, Duncan said:

The other thing that comes to mind is a failed g sensor, but it might be tricky to swap it for a different unit if there are not a lot of other GTRs around

I was told if the g sensor was faulty I would’ve gotten a 4wd warning light. But regardless I found 2 after market g sensors that I may also purchase just in case.

[joshuaho96]

18 hours ago, dodo1410 said:

Hey Duncan, yeah the 4wd light works fine on ignition and turns off normally with all the other lights, and as for the motec wiring it’s spliced in. I’m going back to the shop to check the ecu pins as you’ve mentioned as that could be the culprit.

 

thanks, I’ll keep you updated.

Not sure what spliced in means but almost certainly it's a sensor input making the ATTESA controller think that it needs to engage the transfer case. Test all the inputs and make sure they're sane values before moving on.

[dodo1410]

Can you guide me a bit on where to look so I can test out the input values. 
 

thanks.

[dodo1410]

4 hours ago, joshuaho96 said:

Not sure what spliced in means but almost certainly it's a sensor input making the ATTESA controller think that it needs to engage the transfer case. Test all the inputs and make sure they're sane values before moving on.

 

Just now, dodo1410 said:

Can you guide me a bit on where to look so I can test out the input values. 
 

thanks.

 

[joshuaho96]

3 hours ago, dodo1410 said:

Can you guide me a bit on where to look so I can test out the input values. 
 

thanks.

All g sensors should indicate 2.5V at rest. Throttle signal should be about 0.4V at rest and go up to 4V at WOT coming from the ECU. ECU speed signal should be roughly what the vehicle speed is in reality when everything isn't slipping. Verify the wheel speed sensors are outputting sane, clean signals. Make sure the g sensor is 2.5V at rest and reacts a little if you wobble it back and forth. Don't go crazy with it, nothing more than about 1g in any direction. Do not drop the sensor or you will damage it. Make sure all sensor signals don't drop out or show signs of excessive noise. Make sure your brake light switch is not broken.

You can also crack open the control unit and check the board for signs of tin whiskers (unlikely on a leaded solder board but hey), burned contacts, cold joints, popped capacitors, dead diodes, dead individual transistors, etc.

Testing this is a lot easier if you can just ask the ATTESA controller what it sees. You need a proper Consult scan tool or something that supports the Consult 1/2 protocols for the ABS/ATTESA controller to do that though. The data output from the Consult port would look like this:

Edited January 31 by joshuaho96

[dodo1410]

43 minutes ago, joshuaho96 said:

All g sensors should indicate 2.5V at rest. Throttle signal should be about 0.4V at rest and go up to 4V at WOT coming from the ECU. ECU speed signal should be roughly what the vehicle speed is in reality when everything isn't slipping. Verify the wheel speed sensors are outputting sane, clean signals. Make sure the g sensor is 2.5V at rest and reacts a little if you wobble it back and forth. Don't go crazy with it, nothing more than about 1g in any direction. Do not drop the sensor or you will damage it. Make sure all sensor signals don't drop out or show signs of excessive noise. Make sure your brake light switch is not broken.

You can also crack open the control unit and check the board for signs of tin whiskers (unlikely on a leaded solder board but hey), burned contacts, cold joints, popped capacitors, dead diodes, dead individual transistors, etc.

Testing this is a lot easier if you can just ask the ATTESA controller what it sees. You need a proper Consult scan tool or something that supports the Consult 1/2 protocols for the ABS/ATTESA controller to do that though. The data output from the Consult port would look like this:

Alright thanks a lot I’ll sit down with a few guys and start working on this, I really appreciate it Joshua 

[Pey32]

Hi mate just wondering if you fixed the issue? I recently had the same issue after having some work done. I found that the front right wheel speed sensor had been taken out and not put back in all the way. There was also metal shavings stuck to it. I cleaned these off then re installed it and now it works as it always did. 

[dodo1410]

Hey, I unplugged the speed sensors and cleaned off some shavings on both sides and that still didn’t fix the issue, I’ll try something else and update you guys 

On 2/13/2024 at 11:31 AM, Pey32 said:

Hi mate just wondering if you fixed the issue? I recently had the same issue after having some work done. I found that the front right wheel speed sensor had been taken out and not put back in all the way. There was also metal shavings stuck to it. I cleaned these off then re installed it and now it works as it always did. 

 

[joshuaho96]

1 hour ago, dodo1410 said:

Hey, I unplugged the speed sensors and cleaned off some shavings on both sides and that still didn’t fix the issue, I’ll try something else and update you guys 

 

Check grounds, see what happens if you unplug the ATTESA fuses.

[dodo1410]

I solved the issue, they disconnected the oem TPS and replaced it with a custom motec one, circled in yellow on the picture. They canceled that and put back the oem sensor which is circled in red, and added a motec wire to it to let the ecu read it.

 

had another slight issue where my torque would engage even when cruising but that was just low Tyre pressure. The gtr is fully fixed now with no issues, thanks for all the help guys.

[GTSBoy]

As usual, it's always something from left field!

[joshuaho96]

TPS input voltage being higher than the ATTESA expects will cause weirdness for sure. Also goes to show diagnosing these faults is never a dull moment it seems.

Edited March 22 by joshuaho96