R32 GTR Limp Mode?

[Nydt]

Hey y'all, I have a completely stock 1991 R32 GTR, yesterday I took my car out and went for about a thirty minute drive. It was fine on the way there but when returning home I think the car might have gone into a limp mode. I was cruising in 5th gear around 130km/h, the hicas light came on and there was a significant loss of power. About a minute later I hear a thump, the car starts driving normal again and is fine the rest of the drive back.

This is the second time its happened, same as now it was fine on the trip there. On the way back it had the hicas light on but that time I would feel the power going in and out before hearing the same thump and it being fine. 

I have no idea idea what causing this, but if anyone has any ideas it would be great as a start chasing the cause of this. Also I can provide more details if needed.

Thank you

[GTSBoy]

A HICAS fault really should not cause the engine to go into limp mode. These cars are so old that the systems barely talk to one another.

The thump might be the lockoff solenoid valve for the HICAS (the safety valve) getting closed, to lock the rear wheels "straight". I say "straight", because when my HICAS used to shit itself before I took off and nuked it from orbit, it would lock up with the rear wheels wildy non-straight and you'd need 45° of steering wheel to drive straight.

Take off and nuke it from orbit. First step is to pull the smaller of the two plugs out of the HICAS CU. See if it stops misbehaving.

You can also (whilst leaving it plugged in) try to get the HICAS CU into diagnostic mode by doing the pedal dance, or by connecting a CONSULT capable diagnostic reader into the car and seeing what it has to say for itself. Can't do either of these with it unplugged though.

1st gen HICAS is a ballache. I would do a complete delete. I did do a complete delete.

[Duncan]

wow, a completely stock GTR!

I've got to admit, I have no idea from what you are describing....do you have  any idea where the "thump" comes from, and are you certain it is the HICAS light not something else like the cat overheat light?

[Nydt]

On 08/06/2025 at 3:40 AM, Duncan said:

wow, a completely stock GTR!

I've got to admit, I have no idea from what you are describing....do you have  any idea where the "thump" comes from, and are you certain it is the HICAS light not something else like the cat overheat light?

I have no idea where the thump is coming from, it sounds like its from behind me but im not exactly sure. And it was the HICAS light that came on.

 

On 08/06/2025 at 2:12 AM, GTSBoy said:

A HICAS fault really should not cause the engine to go into limp mode. These cars are so old that the systems barely talk to one another.

The thump might be the lockoff solenoid valve for the HICAS (the safety valve) getting closed, to lock the rear wheels "straight". I say "straight", because when my HICAS used to shit itself before I took off and nuked it from orbit, it would lock up with the rear wheels wildy non-straight and you'd need 45° of steering wheel to drive straight.

Take off and nuke it from orbit. First step is to pull the smaller of the two plugs out of the HICAS CU. See if it stops misbehaving.

You can also (whilst leaving it plugged in) try to get the HICAS CU into diagnostic mode by doing the pedal dance, or by connecting a CONSULT capable diagnostic reader into the car and seeing what it has to say for itself. Can't do either of these with it unplugged though.

1st gen HICAS is a ballache. I would do a complete delete. I did do a complete delete.

I think a complete delete is the route im going to go. Probably going to pick up the kit within the next month and get it installed. HICAS is just going to end up being a headache if I keep it. 

 

Thanks you. 

[joshuaho96]

Just now, Nydt said:

I have no idea where the thump is coming from, it sounds like its from behind me but im not exactly sure. And it was the HICAS light that came on.

 

I think a complete delete is the route im going to go. Probably going to pick up the kit within the next month and get it installed. HICAS is just going to end up being a headache if I keep it. 

 

Thanks you. 

Join the NorCal facebook group btw, but if you can confirm it is HICAS I would install a lock bar and do the work to keep the HICAS control unit happy despite the hardware not functioning. The HICAS control unit is also responsible for speed sensitive power steering so if it's unhappy you'll get failsafe/heavy power steering. A standalone can control that power steering solenoid valve but sometimes it's just easier to stick with the factory setup. Tomei makes a little electronic module that you can install to fool the control unit. I would probably go through the effort to not use a scotch-lok and build a harness so I don't have to chop up the OEM harness. Where you could source those connectors and pins I wouldn't know at the moment though.

[GTSBoy]

R32 HICAS, so long as the CU is not itself faulty, is easy to keep working enough for the PS. Just unplug the smaller of the two loom plugs, on the CU, like I have already said about 4000 times on this forum.

This works with all the stock hardware, or with a lock bar, or with a complete removal. I know, because I have done all of them. OK, actually, I never put a lock bar on because why would you put a lock bar on when you can get rid of the whole lot, including the stupid tie rod ends?

[niZmO_Man]

Try unplugging the smaller plug from the controller under the parcel shelf. right side when standing at the boot (HICAS controller). It's sort of saved me from the car killing me (HICAS spazzing out),