Cruise Control Will Not Set

[lbs_ft]

Hey all, I've got a manual 1990 NA 300ZX with close to 200,000 miles.

A month ago, I went to set the cruise control and realized it would not set. The Cruise Control light comes on, but the Cruise light doesn't illuminate when the Set button is pressed.

Since that time, I've read numerous threads on this forum and many others in an attempt to figure out why mine is not working and how to remedy it.

The following is a list of checks that I've performed using the procedures and schematics outlined in the factory service manual:

Here are the pages from the FSM:

ASCD Schematic

ASCD Diagnostic Procedure

ASCD Actuator

The ASCD module receives 12v to pin 4 when the Cruise Control On/Off button is pressed, and the ASCD hold relay can be heard clicking within the dash.

All pedal switches were removed, tested via multimeter, and reinstalled to the correct positions. Green bumpers are intact and making contact. When the pedals are not pressed, the ASCD module receives 12v to pin 5. When either of the pedals are pressed, pin 5 loses 12v.

When the brake pedal is pressed, pin 11 receives 12v.

When the Set button is pressed, pin 2 receives 12v.

When the Resume button is pressed, pin 1 receives 12v.

When the cancel button is pressed, pins 11 and 2 receive 12v.

Pin 3 on the module has continuity to ground.

Pin 8 on the module has continuity to pin 1 on the actuator.

Pin 9 on the module has continuity to pin 4 on the actuator.

Pin 10 on the module has continuity to pin 2 on the actuator.

Pin 3 on the actuator has continuity to ground.

Hooking power to pin 1 and ground to pin 4 on the actuator powers up the actuator pump.

Hooking power to pins 1, 2, and 3 on the actuator powers up the actuator pump and pulls the throttle cable back.

While powered up, removal of power to pin 1 on the actuator causes the throttle cable to return immediately.

While powered up, removal of ground to pin 4 on the actuator causes the throttle cable to return immediately. (The actuator test procedure in the manual says this should return in 50-60 seconds, but it was almost instantaneous for me.)

Disassembled the set/resume/cancel switch assembly and replaced the tactile microswitches within.

Purchased a used ASCD module from Z1 Motorsports and replaced my factory module.

Tested the speed sensor at the ASCD module. The multimeter recorded pulses when the rear wheels were spun, I believe something around .4v, increasing in frequency as the wheels were spun faster.

Having tested literally every connection leading to and from the ASCD module, as well as replacing the module itself, I'm 100% at a loss as to where to go from here.

Barring replacement of the actuator, the speed sensor, or re-replacement of the ASCD module (it would be s*** luck, but its possible), I'm totally lost. I hate throwing money at a problem, especially when I'm not sure that it will fix said problem.

I design electrical schematics by trade, so I've got my hands on the schematics provided in the manual and the concepts of how this should work are second nature to me, but that's really what makes this that much harder. It just doesn't make sense.

Any and all help would be greatly appreciated! Thanks in advance.

[kevin43734]

Not sure how much help this will be but I once had a Subaru WRX with a cruise control issue as well. What fixed it? - it was a blow fuse to the radio. My point is I think you have hit everything. Start looking at all the fuses if you haven't already and make sure ECU isn't throwing codes. Even if it seems unrelated, if it is electrical and it isn't working fix it. Could be a ground too. Best of luck. These problems are a pain in the you know what.

[Z-bass]

Please review my post entitled "Mystery code 14".....

[Joel S]

have you checked to make sure you are getting a good vacuum feed to the module in the engine bay. And that your cables are hooked up. i know its simple but on mine they had shoved them along the firewall and looked hooked up even though they weren't.

[1991_300ZX]

Did you fix it?
I have a 1990 i'm parting out,, everything in perfect shape, all cruise parts good.

[ZX-Smoov]

My cruise control issue was a part missing. A little part that looks like and feels like a gummy bear. It goes behind the accelerator pedal if I'm not mistaken (been a few years) but perhaps someone has a link to purchase with the part number. It's an inexpensive rubber part between 6-12 bucks.