I've blown 2 Active Suspension CU's and need help

[carlosinseattle]

I bought a 1994 Q45A as a project car last fall and I'm trying to restore it. When I first bought it, the CU for the active worked fine, and I could retrieve codes with the onboard diagnostics (Switching the N/H switch 10 times, you know the routine). Now I can't do that, and I'm perplexed as to why. The first CU worked fine and I was able to get the codes and repair as neccessary. Obviously the first code was 45, which is low fluid. I added the fluid, then got code 41. After some time, 3 months as the car sat idle, I went to work on it again. Then the active computer failed. So I decided to change out the pump solenoids because I thought that was causing the problem. I changed out the pump solenoids, but the CU still would not work. I bought a CU from a local guy from a car that I knew worked. The CU still threw out a code 41. I knew the solenoids worked because they came from a working car, so I went through the diagnostic procedures to rule out the problems. The solenoid connector and then the connector for the fail safe valve. They then checked out OK, but now my CU won't show anything; no code 55, or 41, or any code. The yellow light just stays lit, but won't show codes. What am I doing wrong? What's causing this to happen? Any help you could offer is appreciated.

[silver2k2]

I am experienceing the same problem with my car. It simply will not go into diagnosis mode. Sorry I cant be of more help. Have you tried pulling the neg cable to reset the computer. That worked once for me

[texasoil]

I believe it is a problem with the batteries. A 'full' battery can show 13.2 volts with no load, but drop to 7 or8 when cranking if its worn out. That low voltage will screw up any of the Q45 computers, and the 'active' computer is farthest away and a rather big consumer. Have your battery load tested by your friendly parts store. FREE. Have alternator load tested also.

[maxnix]

New batteries are like new fluids, de rigeur to replace them when age or quality is unknown, or greater than two years.

[qship96]

I agree,as my experience with q45 oem batteries has been death at 3.5 years almost to the day-replace every 36.0 months and never worry about it.

[carlosinseattle]

Brand new battery and alternator. I've disconnected the battery terminals several times to see if the system would reset; to no avail. Before I replaced the battery and alternator I had other problems, like the seat warmers would not work on occasion. Is there a way to have the car's electrical system tested to see if there are open circuits? And if so, could that cause my problem? I am getting my old alternator tested today to see if it comes up a a good one. It was load tested on the car and failed, which is why I bought the other alternator. The battery is brand new. Is there some main power regulator that can cause these problems?

"Texasoil" said he ahrd a hard time believing the active computer is broken too. This is getting rather frustrating!!!

[metaverse3]

Check every grounding point in that vehicle, and clean (within reach)

[carlosinseattle]

Good idea!!

I'll check tonight when I get home.Does anyone know where the "B18" body ground is located?

Also, just to be certain: Is there an Active Suspension Relay somewhere? I know about the fuses, but is there a relay somewhere?

[silver2k2]

I have a brand new alternator and battery as well.

[carlosinseattle]

I've checked everything, including all the body ground locations. The connector has all the appropriate grounds connected when I checked by going throught the diagnostic procedure. Even the switch came out OK, not perfect, but that's because the computer isn't sending the correct signals. I'd like for someone to test one of my computers in their car and let me know if it works. I'm tired of chasing down active suspension CU's. And it still doesn't tell me why my system is not working.

Can the dealer tell me what's wrong, by using their consult diagnostic tool, even if the active computer isn't working properly?

CR

[3Q Jay]

doubtful. my black has the dreaded occasional actsus lite (it ALWAYS shows code 55, however), but the PO took it in to dealer the week before i bought it and of course they could find nothing wrong.

seems that especially on the '94 models (maybe '95 too), that the active CU has problems right after an alternator failure.

Silver still has her original alternator. i keep meaning to change it preemptively (nissan reman'd sitting in my garage), but just not finding the time....

[carlosinseattle]

Any other Q45A owners near Seattle, WA? I'll drive to wherever you are to try to figure this out. Does anyone maybe even have a friend that doesn't use this forum, but might be willing to try this?

Carlos

[3Q Jay]

Carlos- i'd be happy to try it out, but i can't get to it for a while.

i also have a spare that you could try (be warned though, it gave an actsus light when i put it in silver).

Jay