Hicas / Rear Steering Rack

[jrm]

Hi all,

I was recently found to have some excessive movement in my rear steering rack - we suspect due to running with the HICAS fuse out for an extended period after there were issues with it.

The mechanic I used fitted a replacement steering rack from a low-km R34, however I found that now after I got home - the HICAS light will not go out. I ran the HICAS diagnostic and it came up with the following codes:

21 Vehicle speed sensor not present

22 Steering angle sensor not present

23 Steering angle sensor neutral or not present

24 Rear main sensor input not present

25 Rear sub sensor input not present

We've double-checked all of the ground-points, and sensor connectors and even swapped the sensors back from my original rack - still doesn't seem to change anything. Given that it's basically every sensor fault possible, I'm at a bit of a loss and wondering if it's a bigger wiring issue or the HICAS ECU is playing up. But seems a bit coincidental it would die after changing the rack after being good on the car for many years that I've owned it.

I'm back at the mechanic today, and we're going to play around some more - I'm guessing maybe he'll try a different rack if it keeps playing up

Does anyone have any suggestions, tips or has anyone seen this sort of thing happen before when changing the rear rack?

[frankiman]

maybe a plug to/from the hicas ECU (which is in the trunk) hasn't been plugged back in correctly

[jrm]

The mechanic who changed the rack over has had the car for two days how, tried swapping every sensor, every piece of wiring he can find and even putting the original rack in and can't get it to clear.

Only thing he can think of is that the error codes need to clear from the HICAS ECU and that I'm going to need to see nissan about it - this sounds like complete baloney to me. Anyone have any ideas? I'm getting very very frustrated.

Jenna

[jrm]

Well, after the mechanic blamed the HICAS ecu needing a reset, and after digging through many threads, and printing out 70+ pages of nissan workshop information from the R34 and M35 (for the HICAS specific tests which arent listed in the R34 service manual), I found no references to HICAS being able to be reset through CONSULT. At this point, as much as I'd called up Nissan and they were happy to check it out (for a fee) I felt it was probably best to utilise the diagnostic information in the service manuals to try and see what on earth was wrong.

So, this Sunday my partner and I ended up and having a poke around. I'll admit, most of the hard work was done by my awesomely talented electronics technician trained other half. Thank-you!

We started out by checking the voltages to the HICAS ECU in the boot, which all verified fine against the figures in the service manual, so that ruled out any wiring issues to the HICAS ECU. The HICAS ECU was also only errorring for the sensors during a diagnostic, which suggested that it was operating fine anyway - but it doesn't hurt to follow the service manual procedures and check for good grounds, etc.

Anyway, this was followed by jacking the car up, and testing the voltages to each of the sensors on the HICAS rack. Checking the resistance across the various pins with the sensor disconnected showed that the sensor was (or should be) working correctly. Checking the voltage wire on each of the two sensors on the rear rack showed a healthy 5V, exactly what the service manual specified. However, the central signal wire was showing 4mv or something stupidly low. Even after using the adjustment screws to move the sensor - the signal wire did not change. This seemed instantly rather odd as it should have registered different voltages through the adjustment range. This sensor is supposed to (according to the manual) read approximately 2.4V so a few millivolts suggested it was at the maximum of it's resistance.

After ripping off the main sensor, connecting up the loom, and moving the internal potentiometer by hand - the voltages varied as expected - indicating the sensor was definitely not at fault. What *was* found at this point was that the sensor appear to be spring-loaded! This led to the obvious conclusion that this spring needed to be loaded up before putting it back onto the rear rack. The sensor housing, it turns out, has a small lip to grab hold of the spring-loaded as it unloads so that it keeps the sensor centered and loaded up appropriately.

For the sub-rack sensor it was apparently relatively easy to put this on whilst loaded up, but the main rack sensor required a piece of cotton to hold the spring load in place whilst it was put back onto the rack and then the cotton pulled through afterwards. Sure enough, a healthy 2.5V registered on one sensor and 2.45V on the other. Some small adjustments later, and these each read 2.4V (as specified by the service manual).

Starting the car back up, the HICAS light turned itself off as expected. So - that's a result!

I guess more than anything, this is a bit of information for anyone in future who has the situation of removing these sensors or have someone who removes the rear rack and runs into this situation. I can only assume that the mechanic in question did not realise when the sensors were removed as part of changing the racks over that these were spring-loaded and needed to be loaded up. It does seem rather odd, especially seeing as I would have expected you'd hear it unwind. I haven't yet talked to the mechanic about it, so we'll have to see.

All-in-all, I'm chuffed with having a working HICAS and in great debt to my awesome better half for working electronic and mechanical magic to check it all out, figure out the sensors were spring-loaded and and make it all work again.